Science Group

Beaulieu, C., S. A. Henson, Jorge Sarmiento, J. P. Dunne, Ryan R. Rykaczewski, and L. Bopp, 2013: Factors challenging our ability to detect long-term trends in ocean chlorophyll. Biogeosciences, Copernicus Publications, 10, doi:10.5194/bg-10-2711-2013 2711-2724
[ Abstract ]
Global climate change is expected to affect the ocean's biological productivity. The most comprehensive information available about the global distribution of contemporary ocean primary productivity is derived from satellite data. Large spatial patchiness and interannual to multidecadal variability in chlorophyll a concentration challenges efforts to distinguish a global, secular trend given satellite records which are limited in duration and continuity. The longest ocean color satellite record comes from the Seaviewing Wide Field-of-view Sensor (SeaWiFS), which failed in December 2010. The Moderate Resolution Imaging Spectroradiometer (MODIS) ocean color sensors are beyond their originally planned operational lifetime. Successful retrieval of a quality signal from the current Visible Infrared Imager Radiometer Suite (VIIRS) instrument, or successful launch of the Ocean and Land Colour Instrument (OLCI) expected in 2014 will hopefully extend the ocean color time series and increase the potential for detecting trends in ocean productivity in the future. Alternatively, a potential discontinuity in the time series of ocean chlorophyll a, introduced by a change of instrument without overlap and opportunity for cross-calibration, would make trend detection even more challenging. In this paper, we demonstrate that there are a few regions with statistically significant trends over the ten years of SeaWiFS data, but at a global scale the trend is not large enough to be distinguished from noise. We quantify the degree to which red noise (autocorrelation) especially challenges trend detection in these observational time series. We further demonstrate how discontinuities in the time series at various points would affect our ability to detect trends in ocean chlorophyll a. We highlight the importance of maintaining continuous, climate-quality satellite data records for climate-change detection and attribution studies.
Little, C. M., Michael Oppenheimer, and Nathan M. Urban, March 2013: Upper bounds on twenty-first-century Antarctic ice loss assessed using a probabilistic framework. Nature Climate Change, Macmillan Publishers Limited, doi:10.1038/NCLIMATE1845
[ Abstract ]
Climate adaptation and flood risk assessments have incorporated sea-level rise (SLR) projections developed using semi-empirical methods (SEMs) and expert-informed mass-balance scenarios. These techniques, which do not explicitly model ice dynamics, generate upper bounds on twenty-first century SLR that are up to three times higher than Intergovernmental Panel on Climate Change estimates. However, the physical basis underlying these projections, and their likelihood of occurrence, remain unclear. Here, we develop mass-balance projections for the Antarctic ice sheet within a Bayesian probabilistic framework, integrating numerical model output and updating projections with an observational synthesis.Without abrupt, sustained, changes in ice discharge (collapse), we project a 95th percentile mass loss equivalent to ~13 cm SLR by 2100, lower than previous upper-bound projections. Substantially higher mass loss requires regional collapse, invoking dynamics that are likely to be inconsistent with the underlying assumptions of SEMs. In this probabilistic framework, the pronounced sensitivity of upper-bound SLR projections to the poorly known likelihood of collapse is lessened with constraints on the persistence and magnitude of subsequent discharge. More realistic, fully probabilistic, estimates of the ice-sheet contribution to SLR may thus be obtained by assimilating additional observations and numerical models.
Alvarez, Ramón A., Stephen W. Pacala, James J. Winebrake, W. Chameides, and Steven P. Hamburg, 2012: Greater focus needed on methane leakage from natural gas infrastructure. Proceedings of the National Academy of Sciences of the United States of America, doi:10.1073/pnas.1202407109
[ Abstract ]
Natural gas is seen by many as the future of American energy: a fuel that can provide energy independence and reduce greenhouse gas emissions in the process. However, there has also been confusion about the climate implications of increased use of natural gas for electric power and transportation. We propose and illustrate the use of technology warming potentials as a robust and transparent way to compare the cumulative radiative forcing created by alternative technologies fueled by natural gas and oil or coal by using the best available estimates of greenhouse gas emissions from each fuel cycle (i.e., production, transportation and use). We find that a shift to compressed natural gas vehicles from gasoline or diesel vehicles leads to greater radiative forcing of the climate for 80 or 280 yr, respectively, before beginning to produce benefits. Compressed natural gas vehicles could produce climate benefits on all time frames if the well-to-wheels CH₄ leakage were capped at a level 45—70% below current estimates. By contrast, using natural gas instead of coal for electric power plants can reduce radiative forcing immediately, and reducing CH₄ losses from the production and transportation of natural gas would produce even greater benefits. There is a need for the natural gas industry and science community to help obtain better emissions data and for increased efforts to reduce methane leakage in order to minimize the climate footprint of natural gas.
Beaulieu, C., Jorge Sarmiento, S. E. Mikaloff-Fletcher, Jie Chen, and David Medvigy, 2012: Identification and characterization of abrupt changes in the land uptake of carbon. Global Biogeochemical Cycles, American Geophysical Union, 26(GB1007), doi:10.1029/2010GB004024
[ Abstract ]
A recent study of the net land carbon sink estimated using the Mauna Loa, Hawaii atmospheric CO₂ record, fossil fuel estimates, and a suite of ocean models suggests that the mean of the net land carbon uptake remained approximately constant for three decades and increased after 1988/1989. Due to the large variability in the net land uptake, it is not possible to determine the exact timing and nature of the increase robustly by visual inspection. Here, we develop a general methodology to objectively determine the nature and timing of the shift in the net land uptake based on the Schwarz Information Criterion. We confirm that it is likely that an abrupt shift in the mean net land carbon uptake occurred in 1988. After taking into account the variability in the net land uptake due to the influence of volcanic aerosols and the El Niño Southern Oscillation, we find that it is most likely that there is a remaining step increase at the same time (p-values of 0.01 and 0.04 for Mauna Loa and South Pole, respectively) of about 1 Pg C/yr. Thus, we conclude that neither the effect of volcanic eruptions nor the El Niño Southern Oscillation are the causes of the sudden increase of the land carbon sink. By also applying our methodology to the atmospheric growth rate of CO₂, we demonstrate that it is likely that the atmospheric growth rate of CO₂ exhibits a step decrease between two fitted lines in 1988—1989, which is most likely due to the shift in the net land uptake of carbon.
Beaulieu, C., Jie Chen, and Jorge Sarmiento, 2012: Change-point analysis as a tool to detect abrupt climate variations. Philosophical Transactions of the Royal Society, The Royal Society, 370, doi:10.1098/rsta.2011.0383 1228-1249
[ Abstract ]
Recently, there have been an increasing number of studies using change-point methods to detect artificial or natural discontinuities and regime shifts in climate. However, a major drawback with most of the currently used change-point methods is the lack of flexibility (able to detect one specific type of shift under the assumption that the residuals are independent). As temporal variations in climate are complex, it may be difficult to identify change points with very simple models. Moreover, climate time series are known to exhibit autocorrelation, which corresponds to a model misspecification if not taken into account and can lead to the detection of non-existent shifts. In this study, we extend a method known as the informational approach for change-point detection to take into account the presence of autocorrelation in the model. The usefulness and flexibility of this approach are demonstrated through applications. Furthermore, it is highly desirable to develop techniques that can detect shifts soon after they occur for climate monitoring. To address this, we also carried out a simulation study in order to investigate the number of years after which an abrupt shift is detectable. We use two decision rules in order to decide whether a shift is detected or not, which represents a trade-off between increasing our chances of detecting a shift and reducing the risk of detecting a shift while in reality there is none. We show that, as of now, we have good chances to detect an abrupt shift with a magnitude that is larger than that of the standard deviation in the series of observations. For shifts with a very large magnitude (three times the standard deviation), our simulation study shows that after only 4 years the probabilities of shift detection reach nearly 100 per cent. This reveals that the approach has potential for climate monitoring.
Bohlman, S. A., and Stephen W. Pacala, 2012: A forest structure model that determines crown layers and partitions growth and mortality rates for landscape-scale applications of tropical forests. Journal of Ecology, British Ecological Society, 100, doi:10.1111/j.1365-2745.2011.01935.x 508-518
[ Abstract ]
1. We present a model to quantify tropical forest structure and explain variance in dynamic rates (growth and mortality) that is computationally simple and can be applied to landscape-scale forest inventory and, potentially, remote sensing-derived data. 2. The model is a modification of the perfect plasticity approximation (PPA) based on tree allometry, tree locations and sizes. The model quantifies crown area index (CAI) (number of crowns per unit ground area) and assigns trees to crown layers, which determines the expected number of crowns above each tree and thus its light environment. 3. The structural model, parameterized and tested for the Barro Colorado Island, Panama 50-ha forest dynamics plot using data from forest inventories and stereo aerial photographs, reproduces most canopy and understorey structural and dynamic properties. The PPA model worked as well or better than a computationally intensive, spatially explicit model. A single allometry for all trees worked equally well as functional group or species allometries. Models of growth and mortality were always improved by adding crown layers as defined by the PPA model. 4. The mean CAI of the 50-ha plot was 3.1 with low variance. The observed variance was lower than when tree locations were randomized, which drastically lowered the variance in tree density per plot, indicating that there are regulating forces towards a small range of crown area indices. 5. Synthesis. A number of simplifying characteristics in structure were uncovered with the PPA structural model applied to a tropical forest: species allometries were not needed despite the high species diversity in the forest; the model worked on a range of plot sizes; and the variance in CAI was surprisingly low, suggesting regulatory mechanisms. The PPA structural model can be used to develop a fully dynamic simulation model for tropical forests. The ability of the simulation model to predict temporal changes in landscape patterns of biomass, dynamic rates, and species and/or functional group composition will provide validation for the partitioning of dynamic rates by crown layers in the PPA structural model.
Brookshire, E. N. Jack, L.O. Hedin, J. Denis Newbold, Daniel Sigman, and John K. Jackson, January 2012: Sustained losses of bioavailable nitrogen from montane tropical forests. Nature Geosciences, Nature Publishing Group, doi:10.1038/ngeo1372
[ Abstract ]
Tropical forests account for one third of terrestrial primary production and contribute significantly to the land carbon sink^{1, 2}. The future of this sink relies critically on forest interactions with nutrient cycles^{3, 4, 5}. Humid montane tropical forests are often thought to be rich in phosphorus, but to contain low levels of bioavailable nitrogen⁶. Here, we examine the concentration of dissolved nitrogen compounds and the isotopic composition of nitrate in streams in six well-characterized and phosphorus-rich montane forests⁷ in Costa Rica, and in 55 montane forests across Central America and the Caribbean, using data collected between 1990 and 2008. We found high levels of nitrate in these streams, indicative of large losses of bioavailable nitrogen from these forests. We detected no trend in the concentration and isotopic signature of nitrate over the measurement period, implying that high levels of export are neither recent nor episodic. An analysis of the oxygen isotopic signature of stream nitrate showed that exports are sourced from the plant-soil system, rather than from atmospheric deposition that bypasses forest biota. Our findings indicate that nitrogen-rich conditions can develop irrespective of phosphorus availability at the ecosystem scale. We suggest that nitrogen availability may not limit plant growth, or its response to increasing atmospheric carbon dioxide levels, in many montane tropical forests.
Hamme, Roberta C., N. Cassar, Veronica P. Lance, Robert D. Vaillancourt, Michael Bender, Peter G. Strutton, Tommy S. Moore, Michael D. DeGrandpre, C. L. Sabine, D. T. Ho, and Bruce R. Hargreaves, 2012: Dissolved O₂/Ar and other methods reveal rapid changes in productivity during a Lagrangian experiment in the Southern Ocean. Journal of Geophysical Research, American Geophysical Union, 117(C00F12), doi:10.1029/2011JC007046
[ Abstract ]
We use continuous and discrete measurements of the dissolved O₂/Ar ratio in the mixed layer to investigate the dynamics of biological productivity during the Southern Ocean Gas Exchange Experiment in March and April 2008. Injections of SF₆ defined two water masses (patches) that were followed for up to 2 weeks. In the first patch, dissolved O₂/Ar was supersaturated, indicating net biological production of organic carbon. In the second patch, rapidly decreasing O₂/Ar could only be reasonably explained if the mixed layer was experiencing a period of net heterotrophy. The observations rule out dominant contributions from vertical mixing, lateral dilution, or respiration in the ship's underway seawater supply lines. We also compare nine different estimates of net community, new, primary, or gross production made during the experiment. Net community and new production estimates agreed well in the first patch but disagreed in the second patch, both during an initial net heterotrophic period but also during the apparently autotrophic period at the end of the observations. Rapidly changing productivity during the second patch complicated the comparison of methods that integrate over daily and several week timescales. Primary productivity values from on-deck 24 h ¹⁴C incubations and gross carbon production values from photosynthesis-irradiance experiments were nearly identical even during highly dynamic periods of net heterotrophy, while gross oxygen production measurements were 3.5—4.2 times higher but with uncertainties in that ratio near ±2. These comparisons show that the photosynthesis-irradiance experiments based on 1—2 h ¹⁴C incubations underestimated gross carbon production.
Huang, Kuan, Hugh Ducklow, Maria Vernet, N. Cassar, and Michael Bender, 2012: Export production and its regulating factors in the West Antarctica Peninsula region of the Southern Ocean. Global Biogeochemical Cycles, American Geophysical Union, 26(GB2005), doi:10.1029/2010GB004028
[ Abstract ]
In connection with the Palmer LTER program, mixed layer water samples were collected during the cruise of the L.M. Gould in Jan., 2008 at 49 stations on a 20 x 100 km grid in the West Antarctica Peninsula (WAP) region of the Southern Ocean. In this study, [O₂]/[Ar] ratios and the triple isotope composition of dissolved O₂ were measured, and were used to estimate net community O₂ production (NCP) and gross primary O₂ production (GPP), respectively. These estimates are further converted to carbon export production, primary production and the f-ratio. Our measurements give NCP ranging from -3 to 76 mmol O₂ m^-2 day ^-1 (-25 to 650 mg C m ^-2 day ^-1), and GPP from 40 to 220 mmol O₂ m ^-2 day ^-1 (180 to 1010 mg C m ^-2 day ^-1). The O₂ NCP/GPP ratios range from -0.04 to 0.43, corresponding to f-ratios of -0.08 to 0.83. NCP and the NCP/GPP ratio are highest in the northern coastal areas, and decrease to lower values toward the southern coastal area and the open ocean. The inshore-offshore gradient appears to be regulated primarily by iron availability, as supported by the positive correlation between NCP and F_v/F_m ratios (r² = 0.22, p < 0.05). Mixed layer depth (MLD) is inversely correlated with NCP (r² = 0.21, p < 0.002) and NCP/GPP (r² = 0.21, p < 0.02), and highest NCP occurred in the fresh water lenses probably formed from melted coastal glaciers. These results suggest that export production and the f-ratio increase where water stratification is intensified by input of fresh meltwater, and that mixed layer stratification is the major factor regulating NCP in the inner-shelf and coastal regions. Along-shelf variability of phytoplankton community composition is highly correlated with NCP, i.e., NCP increases when the diatom-dominated community in the south transitions to the cryptophyte-dominated one in the north. A high correlation is also observed between NCP and the logarithm of the surface chlorophyll concentration (r² = 0.72, p < 0.0001), which makes it possible to estimate carbon export as a function of Chl a concentration in this region.
Little, C. M., Daniel Goldberg, A. Gnanadesikan, and Michael Oppenheimer, 2012: On the coupled response to ice-shelf basal melting. Journal of Glaciology, 58(208), doi:10.3189/2012JoG11J037 203-215
[ Abstract ]
Ice-shelf basal melting is tightly coupled to ice-shelf morphology. Ice shelves, in turn, are coupled to grounded ice via their influence on compressive stress at the grounding line ('ice-shelf buttressing'). Here, we examine this interaction using a local parameterization that relates the basal melt rate to the ice-shelf thickness gradient. This formulation permits a closed-form solution for a steady-state ice tongue. Time-dependent numerical simulations reveal the spatial and temporal evolution of ice-shelf/ice-stream systems in response to changes in ocean temperature, and the influence of morphology-dependent melting on grounding-line retreat.We find that a rapid (<1 year) re-equilibration in upstream regions of ice shelves establishes a spatial pattern of basal melt rates (relative to the grounding line) that persists over centuries. Coupling melting to ice-shelf shape generally, but not always, increases grounding-line retreat rates relative to a uniform distribution with the same areaaverage melt rate. Because upstream ice-shelf thickness gradients and retreat rates increase nonlinearly with thermal forcing, morphology-dependent melting is more important to the response of weakly buttressed, strongly forced ice streams grounded on beds that slope upwards towards the ocean (e.g. those in the Amundsen Sea).
Tavoni, M., Shoibal Chakravarty, and Robert H. Socolow, 2012: Safe vs. Fair: A Formidable Trade-off in Tackling Climate Change. Sustainability, Basel, Switzerland, MDPI Publishing, 4(2), doi:10.3390/su4020210 210-226
[ Abstract ]
Global warming requires a response characterized by forward-looking management of atmospheric carbon and respect for ethical principles. Both safety and fairness must be pursued, and there are severe trade-offs as these are intertwined by the limited headroom for additional atmospheric CO₂ emissions. This paper provides a simple numerical mapping at the aggregated level of developed vs. developing countries in which safety and fairness are formulated in terms of cumulative emissions and cumulative per capita emissions respectively. It becomes evident that safety and fairness cannot be achieved simultaneously for strict definitions of both. The paper further posits potential global trading in future cumulative emissions budgets in a world where financial transactions compensate for physical emissions: the safe vs. fair tradeoff is less severe but remains formidable. Finally, we explore very large deployment of engineered carbon sinks and show that roughly 1,000 Gt CO₂ of cumulative negative emissions over the century are required to have a significant effect, a remarkable scale of deployment. We also identify the unexplored issue of how such sinks might be treated in sub-global carbon accounting.
Xu, Yan, Dalin Shi, Ludmilla Aristilde, and Francois Morel, 2012: The effect of pH on the uptake of zinc and cadmium in marine phytoplankton: Possible role of weak complexes. Limnology and Oceanography, 57(1), 293-304
[ Abstract ]
In natural samples from the New Jersey coast and the Gulf of Alaska, zinc (Zn) and cadmium (Cd) uptake rates by phytoplankton decreased on average about 30% as pH was decreased from 8.5 to 7.9 or 7.7, and the partial pressure of carbon dioxide (PCO₂) increased accordingly. The underlying mechanism was explored with the model species, Thalassiosira weissflogii and Emiliania huxleyi, using ethylenediaminetetraacetic acid (EDTA), desferrioxamine B, phytochelatin, and cysteine as complexing agents. Experiments with single complexing agents did not reproduce the effect of pH seen in field samples, ruling out two possible mechanisms: a direct effect on the uptake machinery or down-regulation of uptake at high PCO₂. Zn and Cd bioavailability must thus somehow decrease at low pH in natural seawater, which is counterintuitive since the protonation of complexing agents at low pH should increase the total free concentration of metals. However, in the presence of both a strong and a weak complexing agent, metal uptake rate may decrease at low pH if formation of the weak complex decreases and the metal in the weak complex is more "available" than in the strong complex. We obtained proof of concept for such a two-ligand mechanism for Zn uptake in the presence of EDTA ± phytochelatin and EDTA + cysteine. Weak ligands that bind a small fraction of essential metals in surface seawater may thus be important in metal uptake by phytoplankton, and the dual effects of strong and weak complexing agents may control not just the magnitude but also the sign of the effect of pH-PCO₂ on metal uptake rates.
Bender, Michael, Saul Kinter, N. Cassar, and R. Wanninkhof, 2011: Evaluating gas transfer velocity parameterizations using upper ocean radon distributions. Journal of Geophysical Research, American Geophysical Union, 116(C02010), doi:10.1029/2009JC005805
[ Abstract ]
Sea-air fluxes of gases are commonly calculated from the product of the gas transfer velocity (k) and the departure of the seawater concentration from atmospheric equilibrium. Gas transfer velocities, generally parameterized in terms of wind speed, continue to have considerable uncertainties, partly because of limited field data. Here we evaluate commonly used gas transfer parameterizations using a historical data set of ²²²Rn measurements at 105 stations occupied on Eltanin cruises and the Geosecs program. We make this evaluation with wind speed estimates from meteorological reanalysis products (from National Centers for Environmental Prediction and European Centre for Medium-Range Weather Forecasting) that were not available when the ²²Rn data were originally published. We calculate gas transfer velocities from the parameterizations by taking into account winds in the period prior to the date that ²²²Rn profiles were sampled. Invoking prior wind speed histories leads to much better agreement than simply calculating parameterized gas transfer velocities from wind speeds on the day of sample collection. For individual samples from the Atlantic Ocean, where reanalyzed winds agree best with observations, three similar recent parameterizations give k values for individual stations with an rms difference of ~40% from values calculated using ²²²Rn data. Agreement of basin averages is much better. For the global data set, the average difference between k constrained by ²²²Rn and calculated from the various parameterizations ranges from -0.2 to +0.9 m/d (average, 2.9 m/d). Averaging over large domains, and working with gas data collected in recent years when reanalyzed winds are more accurate, will further decrease the uncertainties in sea-air fluxes.
Cassar, N., P. J. DiFiore, B. Barnett, Michael Bender, A. R. Bowie, Bronte Tilbrook, K. Petrou, K. J. Westwood, S. W. Wright, and D. Lefevre, 2011: The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones. Biogeosciences, Copernicus Publications, 8, doi:10.5194/bg-8-227-2011 227-237
[ Abstract ]
The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding of NCP and carbon export production in the Subantarctic Zone (SAZ) and the northern reaches of the Polar Frontal Zone (PFZ), we conducted continuous onboard determinations of NCP as part of the Sub-Antarctic Sensitivity to Environmental Change (SAZ Sense) study, which occurred in January-February 2007. Biological O₂ supersaturation was derived from measuring O₂/Ar ratios by equilibrator inlet mass spectrometry. Based on these continuous measurements, NCP during the austral summer 2007 in the Australian SAZ was approximately 43 mmol O₂ m^-2 d^-1. NCP showed significant spatial variability, with larger values near the Subtropical front, and a general southward decrease. For shallower mixed layers (<50 m), dissolved Fe concentrations and Fe sufficiency, estimated from variable fluorescence, correlated strongly with NCP. The strong correlation between NCP and dissolved Fe may be difficult to interpret because of the correlation of dissolved Fe to MLD and because the concentration of iron may not be a good indicator of its availability. At stations with deeper mixed layers, NCP was consistently low, regardless of iron sufficiency, consistent with light availability also being an important control of NCP. Our new observations provide independent evidence for the critical roles of iron and light in mediating carbon export from the Southern Ocean mixed layer.
Cheung, W., J. P. Dunne, Jorge Sarmiento, and D. Pauly, 2011: Integrating ecophysiology and plankton dynamics into projected maximum fisheries catch potential under climate change in the Northeast Atlantic. ICES Journal of Marine Science, Oxford Journals, doi:10.1093/icesjms/fsr012 1-11
[ Abstract ]
Previous global analyses projected shifts in species distributions and maximum fisheries catch potential across ocean basins by 2050 under the Special Report on Emission Scenarios (SRES) A1B. However, these studies did not account for the effects of changes in ocean biogeochemistry and phytoplankton community structure that affect fish and invertebrate distribution and productivity. This paper uses a dynamic bioclimatic envelope model that incorporates these factors to project distribution and maximum catch potential of 120 species of exploited demersal fish and invertebrates in the Northeast Atlantic. Using projections from the US National Oceanic and Atmospheric Administration�s (NOAA) Geophysical Fluid Dynamics Laboratory Earth System Model (ESM2.1) under the SRES A1B, we project an average rate of distribution-centroid shift of 52 km decade^-1 northwards and 5.1 m decade^-1 deeper from 2005 to 2050. Ocean acidification and reduction in oxygen content reduce growth performance, increase the rate of range shift, and lower the estimated catch potentials (10-year average of 2050 relative to 2005) by 20-30% relative to simulations without considering these factors. Consideration of phytoplankton community structure may further reduce projected catch potentials by ~10%. These results highlight the sensitivity of marine ecosystems to biogeochemical changes and the need to incorporate likely hypotheses of their biological and ecological effects in assessing climate change impacts.
Chisholm, Ryan A., and Stephen W. Pacala, 2011: Theory predicts a rapid transition from niche-structured to neutral biodiversity patterns across a speciation-rate gradient. Theoretical Ecology, Springer, doi:10.1007/s12080-011-0113-5 195-200
[ Abstract ]
A central challenge in community ecology is to predict patterns of biodiversity with mechanistic models. The neutral model of biodiversity is a simple model that appears to provide parsimonious and accurate predictions of biodiversity patterns in some ecosystems, even though it ignores processes such as species interactions and niche structure. In a recent paper, we used analytical techniques to reveal why the mean predictions of the neutral model are robust to niche structure in high diversity but not lowdiversity ecosystems. In the present paper, we explore this phenomenon further by generating stochastic simulated data from a spatially implicit hybrid niche-neutral model across different speciation rates. We compare the resulting patterns of species richness and abundance with the patterns expected from a pure neutral and a pure niche model. As the speciation rate in the hybrid model increases, we observe a surprisingly rapid transition from an ecosystem in which diversity is almost entirely governed by niche structure to one in which diversity is statistically indistinguishable from that of the neutral model. Because the transition is rapid, one prediction of our abstract model is that high-diversity ecosystems such as tropical forests can be approximated by one simple model-the neutral model-whereas low-diversity ecosystems such as temperate forests can be approximated by another simple model-the niche model. Ecosystems that require the hybrid model are predicted to be rare, occurring only over a narrow range of speciation rates.
Downes, S. M., A. Gnanadesikan, Stephen M. Griffies, and Jorge Sarmiento, 2011: Water mass exchange in the Southern Ocean in coupled climate models. Journal of Physical Oceanography, American Meteorological Society, doi:10.1175/2011JPO4586.1
[ Abstract ]
We estimate water mass transformation rates resulting from surface buoyancy fluxes and interior diapycnal fluxes in the region south of 30°S in the ECCO model based state estimation and three free-running coupled climate models. The meridional transport of deep and intermediate waters across 30°S agrees well between models and observationally based estimates in the Atlantic Ocean, but not in the Indian and Pacific where the model based estimates are much smaller. Associated with this, in the models about half the southward flowing deep water is converted into lighter waters and half to denser bottom waters, whereas the observationally-based estimates convert most of the inflowing deep water to bottom waters. In the models, both Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW) are formed primarily via an interior diapycnal transformation rather than being transformed at the surface via heat or freshwater fluxes. Given the small vertical diffusivity specified in the models in this region, we conclude that other processes such as cabbeling and thermobaricity must be playing an important role in water mass transformation. Finally, in the models, the largest contribution of the surface buoyancy fluxes in the Southern Ocean is to convert Upper Circumpolar Deep Water (UCDW) and Antarctic Intermediate Water (AAIW) into lighter Sub-Antarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW).
Downes, S. M., A. S. Budnick, Jorge Sarmiento, and R. Farneti, 2011: Impacts of wind stress on the Antarctic Circumpolar Current fronts and associated subduction. Geophysical Research Letters, American Geophysical Union, 38, L11605, doi:10.1029/2011GL047668
[ Abstract ]
Recent studies suggest that the overturning circulation in the Antarctic Circumpolar Current (ACC) region shows a weak sensitivity to overlying wind stress changes, due to balancing of changes in the eddy-induced and Eulerian mean transports. Using an eddy-permitting coupled climate model, we analyze the response of the ACC transport, and associated water mass subduction rates, in response to an idealized poleward shift and intensification of the westerlies. As in previous studies, we find a small increase in the net ACC transport, and a poleward shift in the mean position of the ACC flow. However, the ACC is restructured, with the Subantarctic Front (SAF) and Polar Front (PF) branches shifting poleward by between 0.9° and 2.5° of latitude, resulting in a weaker ACC flow in both the SAF and PF zones. The wind stress anomaly drives a stronger northward Ekman transport of cool surface waters, deepening the winter mixed layer and causing a 12.7 Sv increase in the subduction of Subantarctic Mode Water (SAMW) north of the SAF zone and a 6.5 Sv increase in the subduction of Antarctic Intermediate Water (AAIW) within the SAF and PF zones. Our results suggest that changes in the wind stress restructure the Southern Ocean large-scale circulation, including the flow of the ACC in its primary jets, and that this affects the formation rates of SAMW and AAIW in this complex region.
Dybzinski, Ray, Caroline Farrior, Adam Wolf, Peter B. Reich, and Stephen W. Pacala, 2011: Evolutionarily Stable Strategy Carbon Allocation to Foliage, Wood, and Fine Roots in Trees Competing for Light and Nitrogen: An Analytically Tractable, Individual-Based Model and Quantitative Comparisons to Data. American Naturalist, 177(2), doi:10.1086/657992 153-166
[ Abstract ]
We present a model that scales from the physiological and structural traits of individual trees competing for light and nitrogen across a gradient of soil nitrogen to their community-level consequences. The model predicts the most competitive (i.e., the evolutionarily stable strategy [ESS]) allocations to foliage, wood, and fine roots for canopy and understory stages of trees growing in oldgrowth forests. The ESS allocations, revealed as analytical functions of commonly measured physiological parameters, depend not on simple root-shoot relations but rather on diminishing returns of carbon investment that ensure any alternate strategy will underperform an ESS in monoculture because of the competitive environment that the ESS creates. As such, ESS allocations do not maximize nitrogen-limited growth rates in monoculture, highlighting the underappreciated idea that the most competitive strategy is not necessarily the "best," but rather that which creates conditions in which all others are "worse." Data from 152 stands support the model�s surprising prediction that the dominant structural trade-off is between fine roots and wood, not foliage, suggesting the "root-shoot" trade-off is more precisely a "root-stem" trade-off for long-lived trees. Assuming other resources are abundant, the model predicts that forests are limited by both nitrogen and light, or nearly so.
Frölicher, T. L., F. Joos, and C.C. Raible, 2011: Sensitivity of atmospheric CO₂ and climate to explosive volcanic eruptions. Biogeosciences, European Geosciences Union, 8, doi:10.5194/bg-8-2317-2011 2317-2339
[ Abstract ]
Impacts of low-latitude, explosive volcanic eruptions on climate and the carbon cycle are quantified by forcing a comprehensive, fully coupled carbon cycle-climate model with pulse-like stratospheric aerosol optical depth changes. The model represents the radiative and dynamical response of the climate system to volcanic eruptions and simulates a decrease of global and regional atmospheric surface temperature, regionally distinct changes in precipitation, a positive phase of the North Atlantic Oscillation, and a decrease in atmospheric CO₂ after volcanic eruptions. The volcanic-induced cooling reduces overturning rates in tropical soils, which dominates over reduced litter input due to soil moisture decrease, resulting in higher land carbon inventories for several decades. The perturbation in the ocean carbon inventory changes sign from an initial weak carbon sink to a carbon source. Positive carbon and negative temperature anomalies in subsurface waters last up to several decades. The multi-decadal decrease in atmospheric CO₂ yields a small additional radiative forcing that amplifies the cooling and perturbs the Earth System on longer time scales than the atmospheric residence time of volcanic aerosols. In addition, century-scale global warming simulations with and without volcanic eruptions over the historical period show that the ocean integrates volcanic radiative cooling and responds for different physical and biogeochemical parameters such as steric sea level or dissolved oxygen. Results from a suite of sensitivity simulations with different magnitudes of stratospheric aerosol optical depth changes and from global warming simulations show that the carbon cycle-climate sensitivity γ , expressed as change in atmospheric CO₂ per unit change in global mean surface temperature, depends on the magnitude and temporal evolution of the perturbation, and time scale of interest. On decadal time scales, modeled γ is several times larger for a Pinatubo-like eruption than for the industrial period and for a high emission, 21st century scenario.
Galbraith, E. D., E. Y. Kwon, A. Gnanadesikan, K. B. Rodgers, Stephen M. Griffies, D. Bianchi, Jorge Sarmiento, J. P. Dunne, J. Simeon, R. D. Slater, Andrew T. Wittenberg, and I. Held, 2011: Climate Variability and Radiocarbon in the CM2Mc Earth System Model. Journal of Climate, American Meteorological Society, doi:10.1175/2011JCLI3919.1
[ Abstract ]
The distribution of radiocarbon (¹⁴C) in the ocean and atmosphere has fluctuated on timescales ranging from seasons to millennia. It is thought that these fluctuations partly reflect variability in the climate system, offering a rich potential source of information to help understand mechanisms of past climate change. Here, a long simulation with a new, coupled model is used to explore the mechanisms that redistribute ¹⁴C within the Earth system on inter-annual to centennial timescales. The model, CM2Mc, is a lower-resolution version of the Geophysical Fluid Dynamics Laboratory's CM2M model, uses no flux adjustments, and incorporates a simple prognostic ocean biogeochemistry model including ¹⁴C. The atmospheric ¹⁴C and radiative boundary conditions are held constant, so that the oceanic distribution of ¹⁴C is only a function of internal climate variability. The simulation displays previously-described relationships between tropical sea surface ¹⁴C and the model-equivalents of the El Niño Southern Oscillation and Indonesian Throughflow. Sea surface ¹⁴C variability also arises from fluctuations in the circulations of the subarctic Pacific and Southern Ocean, including North Pacific decadal variability, and episodic ventilation events in the Weddell Sea that are reminiscent of the Weddell Polynya of 1974-1976. Interannual variability in the air-sea balance of ¹⁴C is dominated by exchange within the belt of intense Southern Westerly winds, rather than at the convective locations where the surface ¹⁴C is most variable. Despite significant interannual variability, the simulated impact on air-sea exchange is an order of magnitude smaller than the recorded atmospheric ¹⁴C variability of the past millennium. This result partly reflects the importance of variability in the production rate of ¹⁴C in determining atmospheric ¹⁴C, but may also reflect an underestimate of natural climate variability, particularly in the Southern Westerly winds.
Hopkinson, Brian M., Christopher L. Dupont, Andrew E. Allen, and Francois Morel, March 2011: Efficiency of the CO₂-concentrating mechanism of diatoms. Proceedings of the National Academy of Sciences of the United States of America, 108(10), doi:10.1073/pnas.1018062108 3830-3837
[ Abstract ]
Diatoms are responsible for a large fraction of CO₂ export to deep seawater, a process responsible for low modern-day CO₂ concentrations in surface seawater and the atmosphere. Like other photosynthetic organisms, diatoms have adapted to these low ambient concentrations by operating a CO₂ concentrating mechanism (CCM) to elevate the concentration of CO₂ at the site of fixation. We used mass spectrometric measurements of passive and active cellular carbon fluxes and model simulations of these fluxes to better understand the stoichiometric and energetic efficiency and the physiological architecture of the diatom CCM. The membranes of diatoms are highly permeable to CO₂, resulting in a large diffusive exchange of CO₂ between the cell and external milieu. An active transport of carbon from the cytoplasm into the chloroplast is the main driver of the diatom CCM. Only one-third of this carbon flux is fixed photosynthetically, and the rest is lost by CO₂ diffusion back to the cytoplasm. Both the passive influx of CO₂ from the external medium and the recycling of the CO₂ leaking out of the chloroplast are achieved by the activity of a carbonic anhydrase enzyme combined with the maintenance of a low concentration of HCO₃⁻ in the cytoplasm. To achieve the CO₂ concentration necessary to saturate carbon fixation, the CO₂ is most likely concentrated within the pyrenoid, an organelle within the chloroplast where the CO₂-fixating enzyme is located.
Joos, F., T. L. Frölicher, Marco Steinacher, and G.-K. Plattner, 2011: Impact of climate change mitigation on ocean acidification projections. Ocean Acidification, Oxford University Press, Chapter 14, 272-290
Kwon, E. Y., Jorge Sarmiento, J. R. Toggweiler, and Tim DeVries, 2011: The control of atmospheric pCO₂ by ocean ventilation change: The effect of the oceanic storage of biogenic carbon. Global Biogeochemical Cycles, American Geophysical Union, 25, doi:10.1029/2011GB004059
[ Abstract ]
A simple analytical framework is developed relating the atmospheric partial pressure of CO₂ to the globally-averaged concentrations of respired carbon (C_soft) and dissolved carbonate (C_carb) in the ocean. Assuming that the inventory of carbon is conserved in the ocean-atmosphere system (i.e. no seawater-sediment interactions), the resulting formula of
ΔpCO₂ / pCO₂
= -0.0053Δ
C_soft + 0.0034Δ C_carb suggests that atmospheric pCO₂ would decrease by 5.3% and increase by 3.4% when C_soft and C_carb increase by 10 μmol kg^-1, respectively. Using this analytical framework along with a 3-D global ocean biogeochemistry model, we show that the response of atmospheric pCO₂ to changes in ocean circulation is rather modest because ~30% of the change in atmospheric pCO₂ caused by the accumulation of respired carbon is countered by a concomitant accumulation of dissolved carbonate in deep waters. Among the suite of circulation models examined here, the largest reduction in atmospheric pCO₂ of 44-88 ppm occurs in a model where reduced overturning rates of both southern and northern sourced deep waters result in a four-fold increase in the Southern Ocean deep water ventilation age. On the other hand, when the ventilation rate of the southern-sourced water decreases, but the overturning rate of North Atlantic Deep Water increases, the resulting decrease in atmospheric pCO₂ is only 14-34 ppm. The large uncertainty ranges in atmospheric pCO₂ arise from uncertainty in how surface productivity responds to circulation change. Although the uncertainty is large, this study suggests that a synchronously reduced rate for the deep water formation in both hemispheres could lead to the large glacial reduction in atmospheric pCO₂ of 80-100 ppm.
Lichstein, J W., and Stephen W. Pacala, 2011: Local diversity in heterogeneous landscapes: quantitative assessment with a height-structured forest metacommunity model. Theoretical Ecology, Springer, 4, doi:10.1007/s12080-011-0121-5 269-281
[ Abstract ]
"Mass effects," in which "sink populations" of locally inferior competitors are maintained by dispersal from "source populations" elsewhere in the landscape, are thought to play an important role in maintaining plant diversity. However, due to the complexity of most quasirealistic forest models, there is little theoretical understanding of the strength of mass effects in forests. Here, we develop a metacommunity version of a mathematically and computationally tractable height-structured forest model, the Perfect Plasticity Approximation, to quantify the strength of mass effects (i.e., the degree of mixing of locally dominant and subordinate species) in heterogeneous landscapes comprising different patch types (e.g., soil types). For realistic levels of inter-patch dispersal, mass effects are weak at equilibrium (i.e., in the absence of disturbance), even in some cases where differences in growth, mortality, and fecundity rates between locally dominant and subordinate species are too small to be reliably detected from field data. However, patch-scale transient dynamics are slow following catastrophic disturbance (in which post-disturbance initial abundances are determined exclusively by immigration) so that at any given time, subordinate species are present in appreciable numbers in most patches. Less severe disturbance regimes, in which some seeds or individuals survive the disturbance, should result in faster transient dynamics (i.e., faster approach to the low-diversity equilibrium). Our results suggest that in order for mass effects to play an important role in tree coexistence, niche differences must be strong enough to prevent neutral drift, yet too weak to be reliably detected from field data.
Martinez-Garcia, Alfredo, A. Rosell-Mele, S. L. Jaccard, Walter Geibert, Daniel Sigman, and G. H. Haug, 2011: Southern Ocean dust-climate coupling over the past four million years. Nature, Macmillan Publishers Limited, 476, doi:10.1038/nature10310 312-316
[ Abstract ]
Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean^1,2. Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40 parts per million by volume (p.p.m.v.) of the decrease (80-100 p.p.m.v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles^3-7. So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (refs 8, 9) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles^5,8,9, providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.
Medvigy, David, and C. Beaulieu, 2011: Trends in daily solar radiation and precipitation coefficients of variation since 1984. Journal of Climate, American Meteorological Society, doi:10.1175/2011JCLI4115.1
[ Abstract ]
This study investigates the possibility of changes in daily-scale solar radiation and precipitation variability. Coefficients of variation (CV) were computed for the daily downward surface solar radiation product from the International Satellite Cloud Climatology Project and the daily precipitation product from the Global Precipitation Climatology Project. Regression analysis was used to identify trends in CV. Statistically significant changes in solar radiation variability were found for 35% of the globe, and particularly large increases were found for tropical Africa and the Maritime Continent. These increases in solar radiation variability were correlated with increases in precipitation variability and increases in deep convective cloud amount. The changes in high-frequency climate variability identified here have consequences for any process depending nonlinearly on climate, including solar energy production and terrestrial ecosystem photosynthesis. In order to assess these consequences, additional work is needed to understand how high-frequency climate variability will change in the coming decades.
O'Reilly, Jessica, Keynyn Brysse, Michael Oppenheimer, and Naomi Oreskes, 2011: Characterizing uncertainty in expert assessments: ozone depletion and the West Antarctic ice sheet. WIREs Climate Change, John Wiley & Sons, Ltd., doi:10.1002/wcc.135
[ Abstract ]
Large-scale assessments have become an important vehicle for organizing, interpreting, and presenting scientific information relevant to environmental policy. At the same time, identifying and evaluating scientific uncertainty with respect to the very questions these assessments were designed to address has become more difficult, as ever more complex problems involving greater portions of the Earth system and longer timescales have emerged at the science-policy interface. In this article, we explore expert judgments about uncertainty in two recent cases: the assessment of stratospheric ozone depletion, and the assessment of the response of the West Antarctic ice sheet (WAIS) to global warming. These assessments were fairly adept at characterizing one type of uncertainty in models (parameter uncertainty), but faced much greater difficulty in dealing with structural model uncertainty, sometimes entirely avoiding grappling with it. In the absence of viable models, innovative approaches were developed in the ozone case for consolidating information about highly uncertain future outcomes, whereas little such progress has been made thus far in the case of WAIS. Both cases illustrate the problem of expert disagreement, suggesting that future assessments need to develop improved approaches to representing internal conflicts of judgment, in order to produce amore complete evaluation of uncertainty.
Palter, J. B., M. Susan Lozier, Jorge Sarmiento, and Robert H. Williams, 2011: The supply of excess phosphate across the Gulf Stream and the maintenance of subtropical nitrogen fixation. Global Biogeochemical Cycles, American Geophysical Union, 25(GB4007), doi:10.1029/2010GB003955
[ Abstract ]
The subtropical North Atlantic is considered a hot spot for biological nitrogen fixation, with estimated rates between 1 and 20 x 10¹¹ mol nitrogen fixed annually. However, the region's nutrient reservoir beneath the euphotic zone is so enriched in nitrate relative to phosphate that it is perplexing how fixation might be sustained there. Here, we investigate whether the physical transport of excess phosphate into the subtropical gyre is sufficient to sustain nitrogen fixation in the gyre. Specifically, we assess the Ekman advection and isopycnal mixing of excess phosphate to the subtropical North Atlantic, using detailed hydrographic and nutrient sections occupied across the Gulf Stream combined with satellite wind data. Ekman advection and along-isopycnal mixing provide a source of approximately 2 x 10¹⁰ mol yr of excess phosphate in the northwestern subtropics, a physical mechanism that has the potential to support more than 3 x 10¹¹ mol yr^-1 of biological nitrogen fixation, after accounting for alternative sinks of excess phosphate. This excess phosphate supply across the gyre's northern boundary and high nitrogen fixation there offers a mechanism that can explain both the maintenance of subtropical North Atlantic nitrogen fixation in a phosphate-poor environment and help account for the weak gradients in the proxies of fixation observed along interior circulation pathways of the gyre.
Pan, Yude, R. A. Birdsey, Jingyun Fang, R. A. Houghton, Pekka Kauppi, Oliver L. Phillips, Anatoly Shvidenko, Simon L. Lewis, Josep G. Canadell, Philippe Ciais, Robert B. Jackson, and Stephen W. Pacala, et al., 2011: A Large and Persistent Carbon Sink in the World's Forests. Science, 333, doi:10.1126/science.1201609 988-993
[ Abstract ]
The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg C year ^-1) globally for 1990 to 2007. We also estimate a source of 1.3 ± 0.7 Pg C year ^-1 from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C year ^-1 partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year ^-1. Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year ^-1, with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks.
Peters, Catherine A., P. F. Dobson, C. M Oldenburg, Joseph S.Y. Wang, T. C. Onstott, George Scherer, B. Freifeld, T. S. Ramakrishnan, Eric L. Stabinski, Kenneth Liang, and Sandeep Verma, 2011: LUCI: A facility at DUSEL for large-scale experimental study of geologic carbon sequestration. Energy Procedia, Elsevier, 4, doi:10.1016/j.egypro.2011.02.478 5050-5057
[ Abstract ]
LUCI, the Laboratory for Underground CO₂ Investigations, is an experimental facility being planned for the DUSEL underground laboratory in South Dakota, USA. It is designed to study vertical flow of CO₂ in porous media over length scales representative of leakage scenarios in geologic carbon sequestration. The plan for LUCI is a set of three vertical column pressure vessels, each of which is ∼500 m long and ∼1 m in diameter. The vessels will be filled with brine and sand or sedimentary rock. Each vessel will have an inner column to simulate a well for deployment of down-hole logging tools. The experiments are configured to simulate CO₂ leakage by releasing CO₂ into the bottoms of the columns. The scale of the LUCI facility will permit measurements to study CO₂ flow over pressure and temperature variations that span supercritical to subcritical gas conditions. It will enable observation or inference of a variety of relevant processes such as buoyancy-driven flow in porous media, Joule-Thomson cooling, thermal exchange, viscous fingering, residual trapping, and CO₂ dissolution. Experiments are also planned for reactive flow of CO₂ and acidified brines in caprock sediments and well cements, and for CO₂-enhanced methanogenesis in organic-rich shales. A comprehensive suite of geophysical logging instruments will be deployed to monitor experimental conditions as well as provide data to quantify vertical resolution of sensor technologies. The experimental observations from LUCI will generate fundamental new understanding of the processes governing CO₂ trapping and vertical migration, and will provide valuable data to calibrate and validate large-scale model simulations.
Rodgers, K. B., S. E. Mikaloff-Fletcher, D. Bianchi, C. Beaulieu, E. D. Galbraith, A. Gnanadesikan, A. G. Hogg, D. Iudicone, B. R. Lintner, T. Naegler, P. J. Reimer, Jorge Sarmiento, and R. D. Slater, 2011: Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds. Climate of the Past, European Geosciences Union, 7, doi:10.5194/cp-7-1123-2011 1123-1138
[ Abstract ]
Tree ring Δ¹⁴C data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric Δ¹⁴C varied on multi-decadal to centennial timescales, in both hemispheres, over the period between AD950 and 1830. The Northern and Southern Hemispheric Δ¹⁴C records display similar variability, but from the data alone is it not clear whether these variations are driven by the production of ¹⁴C in the stratosphere (Stuiver and Quay, 1980) or by perturbations to exchanges between carbon reservoirs (Siegenthaler et al., 1980). As the sea-air flux of ¹⁴CO₂ has a clear maximum in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the interhemispheric gradient. In this study, model simulations are used to show that Southern Ocean winds are likely a main driver of the observed variability in the interhemispheric gradient over AD950-1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980-2004). This interpretation also implies that there may have been a significant weakening of the winds over the Southern Ocean within a few decades of AD1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds at the Medieval Climate Anomaly to Little Ice Age transition remain unknown. Our process-focused suite of perturbation experiments with models raises the possibility that the current generation of coupled climate and earth system models may underestimate the natural background multi-decadal- to centennial-timescale variations in the winds over the Southern Ocean.
Roy, Tilla, L. Bopp, Marion Gehlen, Birgit Schneider, Patricia Cadule, T. L. Frölicher, Joachim Segschneider, Jerry Tjiputra, Christoph Heinze, and F. Joos, 2011: Regional Impacts of Climate Change and Atmospheric CO₂ on Future Ocean Carbon Uptake: A Multimodel Linear Feedback Analysis. Journal of Climate, 24, doi:10.1175/2010JCLI3787.1 2300-2318
[ Abstract ]
The increase in atmospheric CO₂ over this century depends on the evolution of the oceanic air-sea CO₂ uptake, which will be driven by the combined response to rising atmospheric CO₂ itself and climate change. Here, the future oceanic CO₂ uptake is simulated using an ensemble of coupled climate-carbon cycle models. The models are driven by CO₂ emissions from historical data and the Special Report on Emissions Scenarios (SRES) A2 high-emission scenario. A linear feedback analysis successfully separates the regional future (2010-2100) oceanic CO₂ uptake into a CO₂-induced component, due to rising atmospheric CO₂ concentrations, and a climate-induced component, due to global warming. The models capture the observationbased magnitude and distribution of anthropogenic CO₂ uptake. The distributions of the climate-induced component are broadly consistent between the models, with reduced CO₂ uptake in the subpolar Southern Ocean and the equatorial regions, owing to decreased CO₂ solubility; and reduced CO₂ uptake in the midlatitudes, owing to decreased CO₂ solubility and increased vertical stratification. The magnitude of the climate-induced component is sensitive to local warming in the southern extratropics, to large freshwater fluxes in the extratropical North Atlantic Ocean, and to small changes in the CO₂ solubility in the equatorial regions. In key anthropogenic CO₂ uptake regions, the climate-induced component offsets the CO₂- induced component at a constant proportion up until the end of this century. This amounts to approximately 50% in the northern extratropics and 25% in the southern extratropics and equatorial regions. Consequently, the detection of climate change impacts on anthropogenic CO₂ uptake may be difficult without monitoring additional tracers, such as oxygen.
Socolow, Robert H., and Mary R. English, 2011: Living ethically in a greenhouse In The Ethics of Global Climate Change, Edited by Denis G. Arnold, Cambridge University Press, doi:10.1017/CBO9780511732294.009 170-191
[ Abstract ]
It was made clear at the December 2009 conference on climate change in Copenhagen (Conference of the Parties 15) that the nations of the world are only beginning to concede that they face a common threat. It was widely reported that there was a deep divide at Copenhagen between delegates from "developed" countries and delegates from "developing" countries, and that the depth of the anger of the delegates from developing countries surprised the delegates from developed countries. Should the anger have been surprising? Not only had some of the developed countries - most notably, the USA - failed to take significant steps prior to the meeting to reduce the impacts of their economies on the climate. In addition, the developed countries had come to the meeting to revise the global structure of climate change mitigation such that all countries (or at least all of the major economies) would share the task. This arrangement, all conceded, entailed a sharp departure from the previous structure, in place since the 1992 United Nations Framework Convention on Climate Change, which dealt with equity across nations by dividing the world into two groups of countries with "common but differentiated responsibilities." Only the group of "Annex 1" countries (approximately, the countries of the Organization for Economic Cooperation and Development plus Russia) was obligated to make legally binding mitigation commitments.
Socolow, Robert H., et al., 2011: America's Climate Choices, Committee on America's Climate Choices. National Research Council, The National Academies Press: 144pp.
[ Abstract ]
Climate change is occurring, is very likely caused primarily by the emission of greenhouse gases from human activities, and poses significant risks for a range of human and natural systems. Emissions continue to increase, which will result in further change and greater risks. In the judgment of this report's authoring committee, the environmental, economic, and humanitarian risks posed by climate change indicate a pressing need for substantial action to limit the magnitude of climate change and to prepare for adapting to its impacts.
Socolow, Robert H., et al., 2011: Direct Air Capture of CO₂ with Chemicals, A Technology Assessment for the APS Panel on Public Affairs. American Physical Society, http://www.aps.org/policy/reports/assessments/index.cfm, (June 1, 2011), 94pp.
[ Abstract ]
This report explores direct air capture (DAC) of carbon dioxide (CO₂) from the atmosphere with chemicals. DAC involves a system in which ambient air flows over a chemical sorbent that selectively removes the CO₂. The CO₂ is then released as a concentrated stream for disposal or reuse, while the sorbent is regenerated and the CO₂-depleted air is returned to the atmosphere.
Socolow, Robert H., 2011: High-consequence outcomes and internal disagreements: tell us more, please. Climatic Change, Springer, doi:10.1007/s10584-011-0187-5
[ Abstract ]
This article is one of several in this special double-issue that reports the views of "users" of IPCC reports. I am a user in the sense that I advise the policy-making community and rely on the IPCC reports to provide me with authoritative views on the state of the science. My principal recommendation for making the IPCC more helpful to the policy-making community is to strive in the Fifth Assessment Report (AR5) to communicate fully what the climate science community understands and does not understand about high-consequence outcomes. This will require the AR5 authors to provide vivid information about future worlds where high-consequence outcomes have emerged. It will also require the AR5 authors to reveal any disagreements persisting among them after the give-and-take of the writing process has run its course. In the Fourth Assessment Report (AR4) the presentation of high-consequence outcomes had shortcomings that can be rectified in AR5.
Socolow, Robert H., September 2011: Wedges Reaffirmed. Bulletin of the Atomic Scientists, www.thebulletin.org,
[ Abstract ]
In August 2004 Steve Pacala and I published a paper in Science about climate change mitigation. Its core messages are as valid today as seven years ago, but they have not led to action. Here, I suggest that public resistance can be partially explained by shortcomings in the way advocates of forceful action have presented their case. Addressing these shortcomings might put the world back on the course we identified.
Stock, Charles A., Michael A. Alexander, Nicholas A. Bond, Keith M. Brander, W. Cheung, Enrique N. Curchitser, T. L. Delworth, J. P. Dunne, Stephen M. Griffies, Melissa A. Haltuch, Jonathan A. Hare, Anne B. Hollowed, and Patrick Lehodey, et al., 2011: On the use of IPCC-class models to assess the impact of climate on Living Marine Resources. Progress in Oceanography, Elsevier, 88(1-4), doi:10.1016/j.pocean.2010.09.001 1-27
[ Abstract ]
The study of climate impacts on Living Marine Resources (LMRs) has increased rapidly in recent years with the availability of climate model simulations contributed to the assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Collaboration between climate and LMR scientists and shared understanding of critical challenges for such applications are essential for developing robust projections of climate impacts on LMRs. This paper assesses present approaches for generating projections of climate impacts on LMRs using IPCC-class climate models, recommends practices that should be followed for these applications, and identifies priority developments that could improve current projections. Understanding of the climate system and its representation within climate models has progressed to a point where many climate model outputs can now be used effectively to make LMR projections. However, uncertainty in climate model projections (particularly biases and inter-model spread at regional to local scales), coarse climate model resolution, and the uncertainty and potential complexity of the mechanisms underlying the response of LMRs to climate limit the robustness and precision of LMR projections. A variety of techniques including the analysis of multi-model ensembles, bias corrections, and statistical and dynamical downscaling can ameliorate some limitations, though the assumptions underlying these approaches and the sensitivity of results to their application must be assessed for each application. Developments in LMR science that could improve current projections of climate impacts on LMRs include improved understanding of the multi-scale mechanisms that link climate and LMRs and better representations of these mechanisms within more holistic LMR models. These developments require a strong baseline of field and laboratory observations including long time series and measurements over the broad range of spatial and temporal scales over which LMRs and climate interact. Priority developments for IPCC-class climate models include improved model accuracy (particularly at regional and local scales), inter-annual to decadal-scale predictions, and the continued development of earth system models capable of simulating the evolution of both the physical climate system and biosphere. Efforts to address these issues should occur in parallel and be informed by the continued application of existing climate and LMR models.
Bianchi, D., Jorge Sarmiento, A. Gnanadesikan, R. M. Key, P. Schlosser, and R. Newton, 2010: Low helium flux from the mantle inferred from simulations of oceanic helium. Earth and Planetary Science Letters, (297), doi:10.1016/j.epsl.2010.06.037 Elsevier
[ Abstract ]
The high ³He/⁴He isotopic ratio of oceanic helium relative to the atmosphere has long been recognized as the signature of mantle ³He outgassing from the Earth's interior. The outgassing flux of helium is frequently used to normalize estimates of chemical fluxes of elements from the solid Earth, and provides a strong constraint to models of mantle degassing. Here we use a suite of ocean general circulation models and helium isotope data obtained by the World Ocean Circulation Experiment to constrain the flux of helium from the mantle to the oceans. Our results suggest that the currently accepted flux is overestimated by a factor of 2. We show that a flux of 527±102mol year⁻¹ is required for ocean general circulation models that produce distributions of ocean ventilation tracers such as radiocarbon and chlorofluorocarbons that match observations. This new estimate calls for a reevaluation of the degassing fluxes of elements that are currently tied to the helium fluxes, including noble gases and carbon dioxide.
Brunelle, B. G., Daniel Sigman, S. L. Jaccard, L. D. Keigwin, B. Plessen, G. Schettler, M. S. Cook, and G. H. Haug, 2010: Glacial/interglacial changes in nutrient supply and stratification in the western. Quaternary Science Reviews, Elsevier, (29), doi:10.1016/j.quascirev.2010.03.010 2579-2590
[ Abstract ]
In piston cores from the open subarctic Pacific and the Okhotsk Sea, diatom-bound δ¹⁵N (δ¹⁵N_db), biogenic opal, calcium carbonate, and barium were measured from coretop to the previous glacial maximum (MIS 6). Glacial intervals are generally characterized by high δ¹⁵N_db (w8&) and low productivity, whereas interglacial intervals have a lower δ¹⁵N_db (5.7-6.3 per mil) and indicate high biogenic productivity. These data extend the regional swath of evidence for nearly complete surface nutrient utilization during glacial maxima, consistent with stronger upper water column stratification throughout the subarctic region during colder intervals. An early deglacial decline in δ¹⁵N_db of 2 per mil at ~17.5 ka, previously observed in the Bering Sea, is found here in the open subarctic Pacific record and arguably also in the Okhotsk, and a case can be made that a similar decrease in δ¹⁵N_db occurred in both regions at the previous deglaciation as well. The early deglacial δ¹⁵N_db decrease, best explained by a decrease in surface nutrient utilization, appears synchronous with southern hemisphere-associated deglacial changes and with the Heinrich 1 event in the North Atlantic. This δ¹⁵N_db decrease may signal the initial deglacial weakening in subarctic North Pacific stratification and/or a deglacial increase in shallow subsurface nitrate concentration. If the former, it would be the North Pacific analogue to the increase in vertical exchange inferred for the Southern Ocean at the time of Heinrich Event 1. In either case, the lack of any clear change in paleoproductivity proxies during this interval would seem to require an early deglacial decrease in the iron-to-nitrate ratio of subsurface nutrient supply or the predominance of light limitation of phytoplankton growth during the deglaciation prior to B�lling-Aller�d warming.
Chisholm, Ryan A., and Stephen W. Pacala, 2010: Niche and neutral models predict asymptotically equivalent species abundance distributions in high-diversity ecological communities. Proceedings of the National Academy of Sciences of the United States of America, 107(36), doi:10.1073/pnas.1009387107
[ Abstract ]
Afundamental challenge inecology is tounderstandthemechanisms that govern patterns of relative species abundance. Previous numerical simulations have suggested that complex niche-structured models produce species abundance distributions (SADs) that are qualitatively similar to those of very simple neutral models that ignore differences between species. However, in the absence of an analytical treatment of niche models, one cannot tell whether the two classes of model produce the same patterns via similar or different mechanisms. We present an analytical proof that, in the limit as diversity becomes large, a strong niche model give rises to exactly the same asymptotic form of SAD as the neutral model, and we verify the analytical predictions for a Panamanian tropical forest data set. Our results strongly suggest that neutral processes drive patterns of relative species abundance in high-diversity ecological communities, even when strong niche structure exists. However, neutral theory cannot explain what generates high diversity in the first place, and it may not be valid in low-diversity communities. Our results also confirm that neutral theory cannot be used to infer an absence of niche structure or to explain ecosystem function.
Crevoisier, C., C. Sweeney, M. N. Gloor, Jorge Sarmiento, and P. P. Tans, October 2010: Regional US carbon sinks from three-dimensional atmospheric CO₂ sampling. Proceedings of the National Academy of Sciences of the United States of America, 107(43), doi:10.1073/pnas.0900062107 18348-18353
[ Abstract ]
Studies diverge substantially on the actual magnitude of the North American carbon budget. This is due to the lack of appropriate data and also stems from the difficulty to properly model all the details of the flux distribution and transport inside the region of interest. To sidestep these difficulties, we use here a simple budgeting approach to estimate land-atmosphere fluxes across North America by balancing the inflow and outflow of CO₂ from the troposphere. We base our study on the unique sampling strategy of atmospheric CO₂ vertical profiles over North America from the National Oceanic and Atmospheric Administration/Earth System Research Laboratory aircraft network, from which we infer the three-dimensional CO₂ distribution over the continent. We find a moderate sink of 0.5 � 0.4 PgC y^-1 for the period 2004�2006 for the coterminous United States, in good agreement with the forest-inventory-based estimate of the first North American State of the Carbon Cycle Report, and averaged climate conditions. We find that the highest uptake occurs in the Midwest and in the Southeast. This partitioning agrees with independent estimates of crop uptake in the Midwest, which proves to be a significant part of the US atmospheric sink, and of secondary forest regrowth in the Southeast. Provided that vertical profile measurements are continued, our study offers an independent means to link regional carbon uptake to climate drivers.
DiFiore, P. J., Daniel Sigman, K. L. Karsh, T. W. Trull, Robert B. Dunbar, and R. S. Robinson, 2010: Poleward decrease in the isotope effect of nitrate assimilation across the Southern Ocean. Geophysical Research Letters, American Geophysical Union, 37(L17601), doi:10.1029/2010GL044090 1-5
[ Abstract ]
Recent studies provide seasonally and spatially resolved information on the isotopic characteristics of nitrate supply and N cycling in Southern Ocean surface waters. The new data improve our understanding of the nitrate supply to the Antarctic surface and its isotopic characteristics, especially with regard to the summertime subsurface minimum temperature (T_min) layer in the Antarctic. We use these findings to update and compile estimates of the N isotope effect of nitrate assimilation, ε, in the Southern Ocean near Australia. A poleward decrease in ε emerges, from 8-9% in the Subantarctic Zone (SAZ, 40-52°S) to ~5% in the Polar Antarctic Zone (PAZ, ~66°S). ε is strongly correlated with mixed layer depth at the time of sampling. We hypothesize that the correlation is driven by the physiological response of diatoms to light availability, with light limitation leading to higher cellular efflux of nitrate and thus higher ε.
Dreyfus, G., J. Jouzel, Michael Bender, and Amaelle Landais, et al., 2010: Firn processes and δ¹⁵N: potential for a gas-phase climate proxy. Quaternary Science Reviews, 29(28-42), doi:10.1016/j.quascirev.2009.10.012
[ Abstract ]
In order to quantify the sequence of events between changes in atmospheric composition and climate changes recorded in ice cores, we must accurately account for the age difference between ice and gas at a given depth. This gas age�ice age difference depends on the age of the ice at the bottom of the firn layer, where the bubbles are closed-off. Firn densification models are used to calculate how this age difference varied in the past, but have an uncertainty on the order of 1000 years for central Antarctic sites. Here we explore the possibility that δ¹⁵N of N² is a gas phase proxy of climate, which can be used to synchronize gas and ice records. We present the δ¹⁵N record from the EPICA Dome C (EDC) ice core covering the last three glacial terminations and five glacial-interglacial cycles between 300 and 800 ka. Previous studies have shown that gravitational settling enriches δ¹⁵N as a function of the diffusive column height in the firn. If densification models� prediction of deeper firn close-off under glacial conditions is correct, then we would expect heavier δ¹⁵N during glacial periods, and a negative correlation with temperature. Instead, EDC δ¹⁵N is positively correlated with the ice deuterium content, a proxy for temperature, as previously reported at Vostok, Dome Fuji, and EPICA Dronning Maud Land. We propose a mechanism that links accumulation rate, firn permeability, and convective mixing in the top meters of the firn to explain this correlation between δ¹⁵N and ice deuterium content. The tightest correlation is observed over glacial terminations, supporting the idea that δ¹⁵N is a property in the gas phase that records changes in surface conditions linked to deglacial warming.
Egleston, Eric S., Christopher L. Sabine, and Francois Morel, January 2010: Revelle revisited: Buffer factors that quantify the response of ocean chemistry to changes in DIC and alkalinity. Global Biogeochemical Cycles, AGU, (VOL. 24, GB1002), doi:10.1029/2008GB003407 1-9
[ Abstract ]
We derive explicit expressions of the Revelle factor and several other buffer factors of interest to climate change scientists and those studying ocean acidification. These buffer factors quantify the sensitivity of CO₂ and H⁺ concentrations ([CO₂] and [H+]) and CaCO₃saturation (�� ) to changes in dissolved inorganic carbon concentration (DIC) and alkalinity (Alk). The explicit expressions of these buffer factors provide a convenient means to compare the degree of buffering of [CO₂], [H⁺], and Ω in different regions of the oceans and at different times in the future and to gain insight into the buffering mechanisms. All six buffer factors have roughly similar values, and all reach an absolute minimum when DIC = Alk (pH ~ 7.5). Surface maps of the buffer factors generally show stronger buffering capacity in the subtropical gyres relative to the polar regions. As the dissolution of anthropogenic CO₂ increases the DIC of surface seawater over the next century, all the buffer factors will decrease, resulting in a much greater sensitivity to local variations in DIC and Alk. For example, diurnal and seasonal variations in pH and Ω caused by photosynthesis and respiration will be greatly amplified. Buffer factors provide convenient means to quantify the effect that changes in DIC and Alk have on seawater chemistry. They should also help illuminate the role that various physical and biological processes have in determining the oceanic response to an increase in atmospheric CO₂.
Gloor, M. N., Jorge Sarmiento, and N. Gruber, 2010: What can be learned about carbon cycle climate feedbacks from the CO₂ airborne fraction? Atomsphere Chemistry and Physics Discussion, www.atmos-chem-phys.net/10/7739/2010/, (10), doi:10.5194/acp-10-7739-2010 7739�7751
[ Abstract ]
The ratio of CO₂ accumulating in the atmosphere to the CO₂ flux into the atmosphere due to human activity, the airborne fraction AF, is central to predict changes in earth�s surface temperature due to greenhouse gas induced warming. This ratio has remained remarkably constant in the past five decades, but recent studies have reported an apparent increasing trend and interpreted it as an indication for a decrease in the efficiency of the combined sinks by the ocean and terrestrial biosphere. We investigate here whether this interpretation is correct by analyzing the processes that control long-term trends and decadal-scale variations in the AF. To this end, we use simplified linear models for describing the time evolution of an atmospheric CO₂ perturbation. We find firstly that the spin-up time of the system for the AF to converge to a constant value is on the order of 200�300 years and differs depending on whether exponentially increasing fossil fuel emissions only or the sum of fossil fuel and land use emissions are used. We find secondly that the primary control on the decadal time-scale variations of the AF is variations in the relative growth rate of the total anthropogenic CO₂ emissions. Changes in sink efficiencies tend to leave a smaller imprint. Therefore, before interpreting trends in the AF as an indication of weakening carbon sink efficiency, it is necessary to account for trends and variations in AF stemming from anthropogenic emissions and other extrinsic forcing events, such as volcanic eruptions. Using atmospheric CO₂ data and emission estimates for the period 1959 through 2006, and our simple predictive models for the AF, we find that likely omissions in the reported emissions from land use change and extrinsic forcing events are sufficient to explain the observed long-term trend in AF. Therefore, claims for a decreasing long-term trend in the carbon sink efficiency over the last few decades are currently not supported by atmospheric CO₂ data and anthropogenic emissions estimates.
Gnanadesikan, A., K. A. Emanuel, Gabriel A. Vecchi, Whit G. Anderson, and R. Hallberg, July 2010: How Ocean color can steer Pacific tropical cyclones. Geophysical Research Letters, (InPress),
[ Abstract ]
Because ocean color alters the absorption of sunlight, it can produce changes in sea surface temperatures with further impacts on atmospheric circulation. These changes can project onto fields previously recognized to alter the distribution of tropical cyclones. If the North Pacific subtropical gyre contained no absorbing and scattering materials, the result would be to reduce subtropical cyclone activity in the subtropical Northwest Pacific by 2/3, while concentrating cyclone tracks along the equator. Predicting tropical cyclone activity using coupled models may thus require consideration of the details of how heat moves into the upper thermocline as well as biogeochemical cycling.
Hain, M. P., Daniel Sigman, and G. H. Haug, 2010: Carbon dioxide effects of Antarctic stratification, North Atlantic Intermediate Water formation, and subantarctic nutrient drawdown during the last ice age: Diagnosis and synthesis in a geochemical box model. Global Biogeochemical Cycles, American Geophysical Union, 24, GB4023, doi:10.1029/2010GB003790
[ Abstract ]
In a box model synthesis of Southern Ocean and North Atlantic mechanisms for lowering CO₂ during ice ages, the CO₂ changes are parsed into their component geochemical causes, including the soft�]tissue pump, the carbonate pump, and whole ocean alkalinity. When the mechanisms are applied together, their interactions greatly modify the net CO₂ change. Combining the Antarctic mechanisms (stratification, nutrient drawdown, and sea ice cover) within bounds set by observations decreases CO₂ by no more than 36 ppm, a drawdown that could be caused by any one of these mechanisms in isolation. However, these Antarctic changes reverse the CO₂ effect of the observed ice age shoaling of North Atlantic overturning: in isolation, the shoaling raises CO₂ by 16 ppm, but alongside the Antarctic changes, it lowers CO₂ by an additional 13 ppm, a 29 ppm synergy. The total CO₂ decrease does not reach 80 ppm, partly because Antarctic stratification, Antarctic sea ice cover, and the shoaling of North Atlantic overturning all strengthen the sequestration of alkalinity in the deepest ocean, which increases CO₂ both by itself and by decreasing whole ocean alkalinity. Increased nutrient consumption in the sub�]Antarctic causes as much as an additional 35 ppm CO₂ decrease, interacting minimally with the other changes. With its inclusion, the lowest ice age CO₂ levels are within reach. These findings may bear on the two-stepped CO₂ decrease of the last ice age.
Henson, S. A., Jorge Sarmiento, J. P. Dunne, L. Bopp, I. Lima, S. C. Doney, J. John, and C. Beaulieu, 2010: Detection of anthropogenic climate change in satellite records of ocean chlorophyll and productivity. Biogeosciences, 7, doi:10.5194/bg-7-621-2010 621-640
[ Abstract ]
Global climate change is predicted to alter the ocean�s biological productivity. But how will we recognise the impacts of climate change on ocean productivity? The most comprehensive information available on its global distribution comes from satellite ocean colour data. Now that over ten years of satellite-derived chlorophyll and productivity data have accumulated, can we begin to detect and attribute climate change-driven trends in productivity? Here we compare recent trends in satellite ocean colour data to longer-term time series from three biogeochemical models (GFDL, IPSL and NCAR). We find that detection of climate change-driven trends in the satellite data is confounded by the relatively short time series and large interannual and decadal variability in productivity. Thus, recent observed changes in chlorophyll, primary production and the size of the oligotrophic gyres cannot be unequivocally attributed to the impact of global climate change. Instead, our analyses suggest that a time series of ∼40 years length is needed to distinguish a global warming trend from natural variability. In some regions, notably equatorial regions, detection times are predicted to be shorter (∼ 20−30 years). Analysis of modelled chlorophyll and primary production from 2001� 2100 suggests that, on average, the climate change-driven trend will not be unambiguously separable from decadal variability until ∼2055. Because the magnitude of natural variability in chlorophyll and primary production is larger than, or similar to, the global warming trend, a consistent, decadeslong data record must be established if the impact of climate change on ocean productivity is to be definitively detected.
Hopkinson, Brian M., Yan Xu, Dalin Shi, Patrick J. McGinn, and Francois Morel, 2010: The effect of CO₂ on the photosynthetic physiology of phytoplankton in the Gulf of Alaska. Limnology and Oceanography, 55(5), doi:10.4319/lo.2010.55.5.2011 2011-2024
[ Abstract ]
In the high-nutrient, low-chlorophyll waters of the Gulf of Alaska, microcosm manipulation experiments were used to assess the effect of CO₂ on growth and primary production under iron-limited and iron-replete conditions. As expected, iron had a strong effect on growth and photosynthesis. A modest and variable stimulation of growth and biomass production by CO₂ (high CO₂: 77-122 Pa; low CO₂: 11-17 Pa) was observed under both iron-replete and iron-limited conditions, though near the limit of precision of our measurements in slow-growing low-iron experiments. Physiological acclimations responsible for the changes in growth were assessed. Under iron-limited conditions, growth stimulation at high CO₂ appeared to result from an increase in photosynthetic efficiency, which we attribute to energy savings from down-regulation of the carbon concentrating mechanisms. In some cases, iron-rich photosynthetic proteins (PsbA, PsaC, and cytochrome b⁶) were down-regulated at elevated CO₂ in iron-limited controls. Under iron-replete conditions, there was an increase in growth rate and biomass at high CO₂ in some experiments. This increase was unexpectedly supported by reductions in cellular carbon loss, most likely decreased respiration. We speculate that this effect may be due to acclimation to decreased pH rather than high CO₂. The variability in responses to CO₂ among experiments did not appear to be caused by differences in phytoplankton community structure and may reflect the sensitivity of the net response of phytoplankton to antagonistic effects of the several parameters that co-vary with CO₂.
House, Kurt Z., D. P. Schrag, John D. Higgins, and Elza Olivetti, 2010: The Use of Alkalinity Engineering for CO₂ Mitigation. International Conference on Greenhouse Gas Technologies (GHGT 10), Elsevier/Energy Procedia,
[ Abstract ]
We describe an approach to CO₂ capture and storage from the atmosphere that involves enhancing the solubility of CO₂ in the ocean by a process equivalent to the natural silicate weathering reaction. HCl is electrochemically removed from the ocean and neutralized through reaction with silicate rocks. The increase in ocean alkalinity resulting from the removal of HCl causes atmospheric CO₂ to dissolve into the ocean where it will be stored primarily as HCO3 - without further acidifying the ocean. On timescales of hundreds of years or longer, some of the additional alkalinity will likely lead to precipitation or enhanced preservation of CaCO3, resulting in the permanent storage of the associated carbon, and the return of an equal amount of carbon to the atmosphere. Whereas the natural silicate weathering process is effected primarily by carbonic acid, the engineered process accelerates the weathering kinetics to industrial rates by replacing this weak acid with HCl. In the thermodynamic limit�and with the appropriate silicate rocks�the overall reaction is spontaneous. A range of efficiency scenarios indicates that the process should require 100 - 400 kJ of work per mol of CO₂ captured and stored for relevant timescales. The process can be powered from stranded energy sources too remote to be useful for the direct needs of population centers. It may also be useful on a regional scale for protection of coral reefs from further ocean acidification. Application of this technology may involve neutralizing the alkaline solution that is co-produced with HCl with CO₂ from a point source or from the atmosphere prior to being returned to the ocean.
Jaccard, S. L., E. D. Galbraith, Daniel Sigman, and G. H. Haug, 2010: A pervasive link between Antarctic ice core and subarctic Pacific sediment records over the past 800 kyrs. Quaternary Science Reviews, 29, doi:10.1016/j.quascirev.2009.10.007 206-212
[ Abstract ]
Recently developed XRF core-scanning methods permit paleoceanographic reconstructions on timescales similar to those of ice-core records. We have investigated the distribution of biogenic barium (Ba/Al), opal and carbonate (Ca/Al) in a sediment core retrieved from the abyssal subarctic Pacific (ODP 882, 50°N, 167°E, 3244 m) over an interval that spans the full length of the EPICA Dome C (EDC) ice-core record. Ba/Al and biogenic opal show a strong resemblance to the EDC δD and CO₂, with generally high concentrations during interglacials and lower values during ice ages of the past 800 kyrs. The sedimentary Ba/Al and biogenic opal are most easily interpreted as indicating a reduced sinking flux of organic matter from the surface ocean during cold periods. The Ba/Al maxima during peak interglacials are accompanied by transient Ca/Al peaks in these otherwise carbonate-devoid sediments, which are best explained by a deepening of the calcite lysocline, presumably due to reduced storage of respired CO₂ in the deep North Pacific. For most of the ��luke-warm�� interglacials noted between 420 and 750 ka in EDC, the Ba/Al peaks in ODP 882 are also lower, further strengthening the evidence for a simple physical link between global climate and the biogeochemistry of the subarctic Pacific.
Lichstein, J W., J. Dushoff, Kiona Ogle, Anping Chen, D. W. Purves, J. P. Caspersen, and Stephen W. Pacala, 2010: Unlocking the forest inventory data: relating individual tree performance to unmeasured environmental factors. Ecological Applications, (20(3)), doi:10.1890/08-2334.1 684-699
[ Abstract ]
Geographically extensive forest inventories, such as the USDA Forest Service's Forest Inventory and Analysis (FIA) program, contain millions of individual tree growth and mortality records that could be used to develop broad-scale models of forest dynamics. A limitation of inventory data, however, is that individual-level measurements of light (L) and other environmental factors are typically absent. Thus, inventory data alone cannot be used to parameterize mechanistic models of forest dynamics in which individual performance depends on light, water, nutrients, etc. To overcome this limitation, we developed methods to estimate species-specific parameters (θ_G) relating sapling growth (G) to L using data sets in which G, but not L, is observed for each sapling. Our approach involves: (1) using calibration data that we collected in both eastern and western North America to quantify the probability that saplings receive different amounts of light, conditional on covariates x that can be obtained from inventory data (e.g., sapling crown class and neighborhood crowding); and (2) combining these probability distributions with observed G and x to estimate θ_G using Bayesian computational methods. Here, we present a test case using a data set in which G, L, and x were observed for saplings of nine species. This test data set allowed us to compare estimates of θ_G obtained from the standard approach (where G and L are observed for each sapling) to our method (where G and x, but not L, are observed). For all species, estimates of θ_G obtained from analyses with and without observed L were similar. This suggests that our approach should be useful for estimating light-dependent growth functions from inventory data that lack direct measurements of L. Our approach could be extended to estimate parameters relating sapling mortality to L from inventory data, as well as to deal with uncertainty in other resources (e.g., water or nutrients) or environmental factors (e.g., temperature).
Naik, V., A. M. Fiore, L. W. Horowitz, and H. B. Singh, et al., 2010: Observational constraints on the global atmospheric budget of ethanol. Atomsphere Chemistry and Physics Discussion, http://www.atmos-chem-phys-discuss.net/10/925/2010/acpd-10-925-2010.pdf, 10, 925-945
[ Abstract ]
Energy security and climate change concerns have led to the promotion of biomass-derived ethanol, an oxygenated volatile organic compound (OVOC), as a substitute for fossil fuels. Although ethanol is ubiquitous in the troposphere, our knowledge of its current atmospheric budget and distribution is limited. Here, for the first time we use a global chemical transport model in conjunction with atmospheric observations to place constraints on the ethanol budget, noting that additional measurements of ethanol (and its precursors) are still needed to enhance confidence in our estimated budget. Global sources of ethanol in the model include 5.0 Tg yr⁻¹from industrial sources and biofuels, 9.2 Tg yr⁻¹ from terrestrial plants, ~0.5 Tg yr⁻¹ from biomass burning, and 0.05 Tg yr⁻¹ from atmospheric reactions of the ethyl peroxide radical (C₂H₅O₂) with itself and with the methyl peroxide radical (CH₃O₂). The resulting atmospheric lifetime of ethanol in the model is 2.8 days. Gas-phase oxidation by hydroxyl radical (OH) is the primary global sink of ethanol in the model (65%), followed by dry deposition to land (25%), and wet deposition (10%). Over continental areas, ethanol concentrations predominantly reflect direct anthropogenic and biogenic emission sources. Uncertainty in the biogenic ethanol emissions estimated at a factor of three may contribute to the 50% model underestimate of observations in the North American boundary layer. Furthermore, current levels of ethanol measured in remote atmospheres are an order of magnitude larger than those explained by surface sources or by in-situ atmospheric production from observed precursor hydrocarbons in the model, suggesting a major gap in understanding. Stronger constraints on the budget and distribution of ethanol and other VOCs are a critical step towards assessing the impacts of increasing use of ethanol as a fuel.
Pacala, Stephen W., et al., 2010: Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements. Committee on Methods for Estimating Greenhouse Gas Emissions; National Research Council, National Academy of Sciences, 124pp.
Palter, J. B., Jorge Sarmiento, A. Gnanadesikan, J. Simeon, and R. D. Slater, 2010: Fueling export production: nutrient return pathways from the deep ocean and their dependence on the Meridional Overturning Circulation. Biogeosciences, 7, doi:10.5194/bg-7-3549-2010 3549�3568
[ Abstract ]
In the Southern Ocean, mixing and upwelling in the presence of heat and freshwater surface fluxes transform subpycnocline water to lighter densities as part of the upward branch of the Meridional Overturning Circulation (MOC). One hypothesized impact of this transformation is the restoration of nutrients to the global pycnocline, without which biological productivity at low latitudes would be significantly reduced. Here we use a novel set of modeling experiments to explore the causes and consequences of the Southern Ocean nutrient return pathway. Specifically, we quantify the contribution to global productivity of nutrients that rise from the ocean interior in the Southern Ocean, the northern high latitudes, and by mixing across the low latitude pycnocline. In addition, we evaluate how the strength of the Southern Ocean winds and the parameterizations of subgridscale processes change the dominant nutrient return pathways in the ocean. Our results suggest that nutrients upwelled from the deep ocean in the Antarctic Circumpolar Current and subducted in Subantartic Mode Water support between 33 and 75% of global export production between 30^◦ S and 30^◦ N. The high end of this range results from an ocean model in which the MOC is driven primarily by windinduced Southern Ocean upwelling, a configuration favored due to its fidelity to tracer data, while the low end results from an MOC driven by high diapycnal diffusivity in the pycnocline. In all models, nutrients exported in the SAMW layer are utilized and converted rapidly (in less than 40 years) to remineralized nutrients, explaining previous modeling results that showed little influence of the drawdown of SAMW surface nutrients on atmospheric carbon concentrations.
Sarmiento, Jorge, M. N. Gloor, N. Gruber, C. Beaulieu, A. R. Jacobson, S. E. Mikaloff-Fletcher, Stephen W. Pacala, and K. B. Rodgers, 2010: Trends and regional distributions of land and ocean carbon sinks. Biogeosciences, www.biogeosciences.net/7/2351/2010/, 7, doi:10.5194/bg-7-2351-2010 2351-2367
[ Abstract ]
We show here an updated estimate of the net land carbon sink (NLS) as a function of time from 1960 to 2007 calculated from the difference between fossil fuel emissions, the observed atmospheric growth rate, and the ocean uptake obtained by recent ocean model simulations forced with reanalysis wind stress and heat and water fluxes. Except for interannual variability, the net land carbon sink appears to have been relatively constant at a mean value of −0.27 PgC yr⁻¹ between 1960 and 1988, at which time it increased abruptly by −0.88 (−0.77 to −1.04) PgC yr⁻¹ to a new relatively constant mean of −1.15 PgC yr⁻¹ between 1989 and 2003/7 (the sign convention is negative out of the atmosphere). This result is detectable at the 99% level using a t-test. The land use source (LU) is relatively constant over this entire time interval. While the LU estimate is highly uncertain, this does imply that most of the change in the net land carbon sink must be due to an abrupt increase in the land sink, LS = NLS � LU, in response to some as yet unknown combination of biogeochemical and climate forcing. A regional synthesis and assessment of the land carbon sources and sinks over the post 1988/1989 period reveals broad agreement that the Northern Hemisphere land is a major sink of atmospheric CO₂, but there remain major discrepancies with regard to the sign and magnitude of the net flux to and from tropical land.
Sarmiento, Jorge, R. D. Slater, J. P. Dunne, A. Gnanadesikan, and M. R. Hiscock, 2010: Efficiency of small scale carbon mitigation by patch iron fertilization. Biogeosciences, 7, doi:10.5194/bg-7-3593-2010 3593�3624
[ Abstract ]
While nutrient depletion scenarios have long shown that the high-latitude High Nutrient Low Chlorophyll (HNLC) regions are the most effective for sequestering atmospheric carbon dioxide, recent simulations with prognostic biogeochemical models have suggested that only a fraction of the potential drawdown can be realized. We use a global ocean biogeochemical general circulation model developed at GFDL and Princeton to examine this and related issues. We fertilize two patches in the North and Equatorial Pacific, and two additional patches in the Southern Ocean HNLC region north of the biogeochemical divide and in the Ross Sea south of the biogeochemical divide. We evaluate the simulations using observations from both artificial and natural iron fertilization experiments at nearby locations. We obtain by far the greatest response to iron fertilization at the Ross Sea site, where sea ice prevents escape of sequestered CO₂ during the wintertime, and the CO₂ removed from the surface ocean by the biological pump is carried into the deep ocean by the circulation. As a consequence, CO₂ remains sequestered on century time-scales and the efficiency of fertilization remains almost constant no matter how frequently iron is applied as long as it is confined to the growing season. The second most efficient site is in the Southern Ocean. The North Pacific site has lower initial nutrients and thus a lower efficiency. Fertilization of the Equatorial Pacific leads to an expansion of the suboxic zone and a striking increase in denitrification that causes a sharp reduction in overall surface biological export production and CO₂ uptake. The impacts on the oxygen distribution and surface biological export are less prominent at other sites, but nevertheless still a source of concern. The century time scale retention of iron in this model greatly increases the long-term biological response to iron addition as compared with simulations in which the added iron is rapidly scavenged from the ocean.
Shi, Dalin, Yan Xu, Brian M. Hopkinson, and Francois Morel, January 2010: Effect of Ocean Acidification on Iron Availability to Marine Phytoplankton. Science, New York, AAAS, (January 14, 2010), doi:10.1126/science.1183517 1-8
[ Abstract ]
The acidification caused by dissolution of anthropogenic CO₂ in the ocean changes the chemistry and, hence, the bioavailability of iron (Fe), a limiting nutrient in large oceanic regions. Here, we show that the bioavailability of dissolved Fe may decline due to ocean acidification. Acidification of media containing various Fe compounds decreases the Fe uptake rate of diatoms and coccolithophores to an extent predicted by the changes in Fe chemistry. A slower Fe uptake by a model diatom with decreasing pH is also seen in experiments with Atlantic surface water. The Fe requirement of model phytoplankton remains unchanged with increasing CO₂ . The ongoing acidification of seawater is likely to increase the Fe-stress of phytoplankton populations in some areas of the ocean.
Sigman, Daniel, M. P. Hain, and G. H. Haug, July 2010: The polar ocean and glacial cycles in atmospheric CO₂ concentration. Nature, 466, doi:10.1038/nature09149 47�55
[ Abstract ]
Global climate and the atmospheric partial pressure of carbon dioxide (p CO₂ ^atm) are correlated over recent glacial cycles, with lower p CO₂ ^atm)during ice ages, but the causes of the p CO₂ ^atm) changes are unknown. The modern Southern Ocean releases deeply sequestered CO₂ to the atmosphere. Growing evidence suggests that the Southern Ocean CO₂ �leak� was stemmed during ice ages, increasing ocean CO₂ storage. Such a change would also have made the global ocean more alkaline, driving additional ocean CO₂ uptake. This explanation for lower ice-age p CO₂ ^atm), if correct, has much to teach us about the controls on current ocean processes.
Turner, Will R., B. A. Bradley, Lyndon D. Estes, Michael Oppenheimer, and David S. Wilcove, August 2010: Climate Change: Helping Nature Survive the Human Response. Conservation International, doi:10.1111/j.1755-263X.2010.00128.x
[ Abstract ]
Climate change poses profound, direct, and well-documented threats to biodiversity. A significant fraction of Earth�s species is at risk of extinction due to changing precipitation and temperature regimes, rising and acidifying oceans, and other factors. There is also growing awareness of the diversity and magnitude of responses, both proactive and reactive, that people will undertake as lives and livelihoods are affected by climate change. Yet to date few studies have examined the relationship between these two powerful forces. The natural systems upon which people depend, already under direct assault from climate change, are further threatened by how we respond to climate change. Human history and recent studies suggest that our actions to cope with climate change (adaptation) or lessen its rate and magnitude (mitigation) could have impacts that match�and even exceed�the direct effects of climate change on ecosystems. If we are to successfully conserve biodiversity and maintain ecosystem services in a warming world, considerable effort is needed to predict and reduce the indirect risks created by climate change.
Xu, Y., C.T. Supuran, and Francois Morel, 2010: Cadmium-carbonic anhyrase (In Press). Handbook of Metalloproteins,
Blackstock, Jason J., D. S. Battisti, K. Caldeira, D. M. Eardeley, J. I. Katz, D. W. Keith, A.A.N. Patrinos, D. P. Schrag, Robert H. Socolow, and S. E. Koonin, 2009: Climate Engineering Responses to Climate Emergencies. NOVIM Group,
[ Abstract ]
Despite efforts to stabilize CO₂ concentrations, it is possible that the climate system could respond abruptly with catastrophic consequences. Intentional intervention in the climate system to avoid or ameliorate such consequences has been proposed as one possible response should such a scenario arise. In a one-week study, the authors of this report conducted a technical review and evaluation of proposed climate engineering concepts that might serve as a rapid palliative response to such climate emergency scenarios.
Because of their potential to induce a prompt (<1 yr) global cooling, this study concentrated on Shortwave Climate Engineering (SWCE) methods for moderately reducing the amount of shortwave solar radiation absorbed by the Earth. The study�s main objective was to outline a decade-long agenda of technical research that would maximally reduce the uncertainty surrounding the benefits and risks associated with SWCE. For rigor of technical analysis, the study focused the research agenda on one particular SWCE concept�stratospheric aerosol injection�and in doing so developed several conceptual frameworks and methods valuable for assessing any SWCE proposal.
Basic physical science considerations, exploratory climate modeling, and the impacts of volcanic aerosols on climate all suggest that SWCE could partially compensate for some effects� particularly net global warming�of increased atmospheric CO₂. However, existing data also reveal important limits to the range of CO₂ impacts that SWCE could ameliorate; for example, ongoing ocean acidification would not be affected, and some categories of climate emergency scenario might prove unresponsive to SWCE. Moreover, significant uncertainty presently surrounds the spatial and temporal response of numerous climate and ecological parameters to SWCE, making the near-term deployment of large-scale SWCE extraordinarily risky.
Components of any comprehensive research agenda for reducing these uncertainties can be divided into three progressive phases: (I) Non-Invasive Laboratory and Computational Research; (II) Field Experiments; and (III) Monitored Deployment. Each phase involves distinct and escalating risks (both technical and socio-political), while simultaneously providing data of greater value for reducing uncertainties.
The core questions that need to be addressed can also be clustered into three streams of research: Engineering (intervention system development); Climate Science (modeling and experimentation to understand and anticipate impacts of the intervention); and Climate Monitoring (detecting and assessing the actual impacts, both anticipated and unanticipated). While a number of studies have suggested the engineering feasibility of specific SWCE proposals, the questions in the Climate Science and Climate Monitoring streams present far greater challenges due to the inherent complexity of temporal and spatial delays and feedbacks within the climate system.
These frameworks are applied to structure the comprehensive research agenda outlined for stratospheric aerosol SWCE in Part 3 of this report. For the Engineering stream, current understanding, questions and methods guiding the necessary research into aerosol material, stratospheric lofting and dispersion are all defined. For the Climate Science and Climate Monitoring streams, emphasis is placed on identifying, predicting and monitoring the response of important climate parameters across four broad categories: Radiative, Geophysical, Geochemical and Ecological. Finally, the components within each stream are identified as belonging to Phase I or II research, and the limits placed by the natural variability of the climate system on what can be learned from low-level Phase II field-testing are roughly assessed.
This report does not attempt to evaluate whether stratospheric aerosol (or any other) SWCE systems should be developed or deployed�or even whether any parts of the outlined research program should be pursued. Such questions are the subject of an intense ongoing debate, involving socio-political and economic issues beyond the scope of this study. This report aims to better inform that debate by elucidating the technical research agenda that would be necessary to reduce the uncertainty in potential SWCE interventions.
Bradley, B. A., Michael Oppenheimer, and David S. Wilcove, 2009: Climate Change and Plant Invasions: Restoration Opportunities Ahead. Global Change Biology, 15(6), doi:10.1111/j.1365-2486.2008.01824.x 1511-1521
[ Abstract ]
Rather than simply enhancing invasion risk, climate change may also reduce invasive plant competitiveness if conditions become climatically unsuitable. Using bioclimatic envelope modeling, we show that climate change could result in both range expansion and contraction for five widespread and dominant invasive plants in the western United States. Yellow starthistle (Centaurea solstitialis) and tamarisk (Tamarix spp.) are likely to expand with climate change. Cheatgrass (Bromus tectorum) and spotted knapweed (Centaurea biebersteinii) are likely to shift in range, leading to both expansion and contraction. Leafy spurge (Euphorbia esula) is likely to contract. The retreat of onceintractable invasive species could create restoration opportunities across millions of hectares. Identifying and establishing native or novel species in places where invasive species contract will pose a considerable challenge for ecologists and land managers. This challenge must be addressed before other undesirable species invade and eliminate restoration opportunities.
Cassar, N., B. Barnett, Michael Bender, J. Kaiser, Roberta C. Hamme, and Bronte Tilbrook, 2009: Continuous High-Frequency Dissolved O₂/Ar Measurements by Equilibrator Inlet Mass Spectrometry. Analytical Chemistry, 81, doi:10.1021/ac802300u 1855-1864
[ Abstract ]
The oxygen (O₂) concentration in the surface ocean is influenced by biological and physical processes. With concurrent measurements of argon (Ar), which has similar solubility properties as oxygen, we can remove the physical contribution to O₂ supersaturation and determine the biological oxygen supersaturation. Biological O₂ supersaturation in the surface ocean reflects the net metabolic balance between photosynthesis and respiration, i.e., the net community productivity (NCP). We present a new method for continuous shipboard measurements of O₂/Ar by equilibrator inlet mass spectrometry (EIMS). From these measurements and an appropriate gas exchange parametrization, NCP can be estimated at high spatial and temporal resolution. In the EIMS configuration, seawater from the ship�s continuous intake flows through a cartridge enclosing a gas-permeable microporous membrane contactor. Gases in the headspace of the cartridge equilibrate with dissolved gases in the flowing seawater. A fused-silica capillary continuously samples headspace gases, and the O₂/Ar ratio is measured by mass spectrometry. The ion current measurements on the mass spectrometer reflect the partial pressures of dissolved gases in the water flowing through the equilibrator. Calibration of the O₂/Ar ion current ratio (32/40) is performed automatically every 2 h by sampling ambient air through a second capillary. A conceptual model demonstrates that the ratio of gases reaching the mass spectrometer is dependent on several parameters, such as the differences in molecular diffusivities and solubilities of the gases. Laboratory experiments and field observations performed by EIMS are discussed. We also present preliminary evidence that other gas measurements, such as N₂/Ar and pCO₂ measurements, may potentially be performed with EIMS. Finally, we compare the characteristics of the EIMS with the previously described membrane inlet mass spectrometry (MIMS) approach.
Chakravarty, Shoibal, A. Chikkatur, H. de Coninck, Stephen W. Pacala, Robert H. Socolow, and M. Tavoni, 2009: Sharing global CO₂ emission reductions among one billion high emitters. Proceedings of the National Academy of Sciences of the United States of America, 106(29), doi:10.1073/pnas.0905232106 11884-11888
[ Abstract ]
We present a framework for allocating a global carbon reduction target among nations, in which the concept of ��common but differentiated responsibilities�� refers to the emissions of individuals instead of nations. We use the income distribution of a country to estimate how its fossil fuel CO₂ emissions are distributed among its citizens, from which we build up a global CO₂ distribution. We then propose a simple rule to derive a universal cap on global individual emissions and find corresponding limits on national aggregate emissions from this cap. All of the world�s high CO₂ emitting individuals are treated the same, regardless of where they live. Any future global emission goal (target and time frame) can be converted into national reduction targets, which are determined by ��Business as Usual�� projections of national carbon emissions and incountry income distributions. For example, reducing projected global emissions in 2030 by 13 GtCO₂ would require the engagement of 1.13 billion high emitters, roughly equally distributed in 4 regions: the U.S., the OECD minus the U.S., China, and the nonOECD minus China. We also modify our methodology to place a floor on emissions of the world�s lowest CO₂ emitters and demonstrate that climate mitigation and alleviation of extreme poverty are largely decoupled.
Chakravarty, Shoibal, Robert H. Socolow, and M. Tavoni, November 2009: A Focus on Individuals Can Guide Nations Towards a Low Carbon World. Climate Science and Policy, http://www.climatescienceandpolicy.eu/2009/11/a-focus-on-individuals-can-guide-nations-towards-a-low-carbon-world/, Nov. 13, 2009,
[ PDF ]
Chakravarty, Shoibal, A. Chikkatur, H. de Coninck, Stephen W. Pacala, M. Tavoni, and Robert H. Socolow, 2009: Reply to Grubler and Pachauri: Developing national obligations from individual emissions. Proceedings of the National Academy of Sciences of the United States of America, 106(43 E124), doi:10.1073/pnas.0911102106
Cheung, W., V. Lam, Jorge Sarmiento, K. Kearney, R. Watson, D. Zeller, and D. Pauly, 2009: Large-scale redistribution of maximum fisheries catch potential in the global ocean under climate change. Global Change Biology, doi:10.1111/j.1365-2486.2009.01995.x
[ Abstract ]
Previous projection of climate change impacts on global food supply focuses solely on production from terrestrial biomes, ignoring the large contribution of animal protein from marine capture fisheries. Here, we project changes in global catch potential for 1,066 species of exploited marine fish and invertebrates from 2005 to 2055 under climate change scenarios. We show that climate change may lead to large scale re-distribution of global catch potential, with an average of 30 - 70% increase in high latitude regions and a drop of up to 40% in the tropics. Moreover, maximum catch potential declines considerably in the southward margins of semi-enclosed seas while it increases in poleward tips of continental shelf margins. Such changes are most apparent in the Pacific Ocean. Among the 20 most important fishing Exclusive Economic Zone (EEZ) regions in terms of their total landings, EEZ regions with the highest increase in catch potential by 2055 include Norway, Greenland, US (Alaska) and Russia (Asia). On the contrary, EEZ regions with the biggest loss in maximum catch potential include Indonesia, USA (excluding Alaska and Hawaii), Chile, and China. Many highly impacted regions, particularly those in the tropics, are socio-economically vulnerable to these changes. 36 Thus, our results indicate the need to develop adaptation policy that could minimize climate change impacts through fisheries. The study also provides information which may be useful to evaluate fisheries management options under climate change.
Cheung, W., V. Lam, Jorge Sarmiento, K. Kearney, R. Watson, and D. Pauly, 2009: Projecting global marine biodiversity impacts under climate change scenarios. Fish and Fisheries, doi:10.1111/j.1467-2979.2008.00315.x
[ Abstract ]
Climate change can impact the pattern of marine biodiversity through changes in species� distributions. However, global studies on climate change impacts on ocean biodiversity have not been performed so far. Our paper aims to investigate the global patterns of such impacts by projecting the distributional ranges of a sample of 1066 exploited marine fish and invertebrates for 2050 using a newly developed dynamic bioclimate envelope model. Our projections show that climate change may lead to numerous local extinction in the sub-polar regions, the tropics and semi-enclosed seas. Simultaneously, species invasion is projected to be most intense in the Arctic and the Southern Ocean. Together, they result in dramatic species turnovers of over 60% of the present biodiversity, implying ecological disturbances that potentially disrupt ecosystem services. Our projections can be viewed as a set of hypothesis for future analytical and empirical studies.
Christensen, Villy, Carl J. Walters, Robert Ahrens, Jacqueline Alder, K. Kearney, and Jorge Sarmiento, 2009: Database-driven models of the world's Large Marine Ecosystems. Ecological Modelling, 220, doi:10.1016/j.ecolmodel.2009.04.041 1984-1996
[ Abstract ]
We present a new methodology for database-driven ecosystem model generation and apply the methodology to the world's 66 currently defined Large Marine Ecosystems. The method relies on a large number of spatial and temporal databases, including FishBase, SeaLifeBase, as well as several other databases developed notably as part of the Sea Around Us project. The models are formulated using the freely available Ecopath with Ecosim (EwE) modeling approach and software. We tune the models by fitting to available time series data, but recognize that the models represent only a first-generation of database-driven ecosystem models. We use the models to obtain a first estimate of fish biomass in the world's LMEs. The biggest hurdles at present to further model development and validation are insufficient time series trend information, and data on spatial fishing effort.
DiFiore, P. J., Daniel Sigman, and Robert B. Dunbar, November 2009: Upper ocean nitrogen fluxes in the Polar Antarctic Zone: Constraints from the nitrogen and oxygen isotopes of nitrate. Geochemistry Geophysics Geosystems, Washington, D.C., American Geophysical Union, doi:10.1029/2009GC002468
[ Abstract ]
[1] We report nitrate nitrogen (N) and oxygen (O) isotope measurements from the seasonally sea ice covered Polar Antarctic Zone (PAZ) south of the Southern Antarctic Circumpolar Front. The ¹⁵N/¹⁴N and ¹⁸O/¹⁶O ratios of nitrate both increase into the summertime surface mixed layer, in strong correlation with the upward decrease in nitrate concentration, the expected result of nitrate assimilation by phytoplankton. Culture studies indicate that algal assimilation of nitrate fractionates the nitrate N and O isotopes equally, while previous field studies suggest that nitrate N and O isotope behavior can be decoupled by euphotic zone nitrification. Our data for the PAZ show strong coupling of the dual isotopes of nitrate, and a numerical model of Antarctic summertime surface layer N cycling fits our observations (including isotopic compositions of both nitrate and suspended particulate N) if the nitrification rate is no more than 6% of the nitrate assimilation rate by phytoplankton. The model estimates that the N isotope effect of nitrate assimilation is 5.0 � 0.7�. This estimate lacks some of the uncertainties associated with previous studies within the Antarctic Circumpolar Current, and it is at the low end of most recent estimates from the Southern Ocean, the range of which we speculatively attribute to an effect of mixed layer depth on the amplitude of isotope discrimination./
Gerber, S., L.O. Hedin, Michael Oppenheimer, Stephen W. Pacala, and E. Shevliakova, 2009: Nitrogen Cycling and Feedbacks in a Global Dynamic Land Model. Global Biogeochemical Cycles, http://www.agu.org/journals/pip/gb/2008GB003336-pip.pdf, doi:10.1029/2008GB003336
[ Abstract ]
Global anthropogenic changes in carbon (C) and nitrogen (N) cycles call for modeling tools that are able to address and quantify essential interactions between N, C, and climate in terrestrial ecosystems. Here, we introduce a prognostic N cycle within the Princeton-GFDL LM3V land model. The model captures mechanisms essential for N cycling and their feedbacks on C cycling: N limitation of plant productivity, the N dependence of C decomposition and stabilization in soils, removal of available N by competing sinks, ecosystem losses that include dissolved organic and volatile N, and ecosystem inputs through biological N fixation.
Our model captures many essential characteristics of C-N interactions, and is capable of broadly recreating spatial and temporal variations in N and C dynamics. The introduced N dynamics improves the model�s short term NPP response to step changes in CO₂. Consistent with theories of successional dynamics, we find that physical disturbance induces strong C-N feedbacks, caused by intermittent N loss and subsequent N limitation. In contrast, C-N interactions are weak when the coupled model system approaches equilibrium. Thus, at steady state many simulated features of the carbon cycle, such as primary productivity and carbon inventories are similar to simulations that do not include C-N feedbacks.
Gruber, N., M. N. Gloor, S. E. Mikaloff-Fletcher, S. C. Doney, S. Dutkiewicz, M. Follows, M. Gerber, A. R. Jacobson, F. Joos, K. Lindsay, , and , et al., 2009: Oceanic Sources, Sinks, and Transport of Atmospheric CO₂. Global Biogeochemical Cycles, 23(GB 1005), doi:10.1029/2008GB003349
[ Abstract ]
We synthesize estimates of the contemporary net air-sea CO₂ flux on the basis of an inversion of interior ocean carbon observations using a suite of 10 ocean general circulation models (Mikaloff Fletcher et al., 2006, 2007) and compare them to estimates based on a new climatology of the air-sea difference of the partial pressure of CO₂ (pCO₂) (Takahashi et al., 2008). These two independent flux estimates reveal a consistent description of the regional distribution of annual mean sources and sinks of atmospheric CO₂ for the decade of the 1990s and the early 2000s with differences at the regional level of generally less than 0.1 Pg C a^-1. This distribution is characterized by outgassing in the tropics, uptake in midlatitudes, and comparatively small fluxes in the high latitudes. Both estimates point toward a small (˜ -0.3 Pg C a^-1) contemporary CO₂ sink in the Southern Ocean (south of 44�S), a result of the near cancellation between a substantial outgassing of natural CO₂ and a strong uptake of anthropogenic CO₂. A notable exception in the generally good agreement between the two estimates exists within the Southern Ocean: the ocean inversion suggests a relatively uniform uptake, while the pCO₂-based estimate suggests strong uptake in the region between 58�S and 44�S, and a source in the region south of 58�S. Globally and for a nominal period between 1995 and 2000, the contemporary net air-sea flux of CO₂ is estimated to be -1.7 � 0.4 Pg C a^-1 (inversion) and -1.4 � 0.7 Pg C a^-1 (pCO₂-climatology), respectively, consisting of an outgassing flux of river-derived carbon of ˜+0.5 Pg C a^-1, and an uptake flux of anthropogenic carbon of -2.2 � 0.3 Pg C a^-1 (inversion) and -1.9 � 0.7 Pg C a^-1 ((pCO₂-climatology). The two flux estimates also imply a consistent description of the contemporary meridional transport of carbon with southward ocean transport throughout most of the Atlantic basin, and strong equatorward convergence in the Indo-Pacific basins. Both transport estimates suggest a small hemispheric asymmetry with a southward transport of between -0.2 and -0.3 Pg C a^-1 across the equator. While the convergence of these two independent estimates is encouraging and suggests that it is now possible to provide relatively tight constraints for the net air-sea CO₂ fluxes at the regional basis, both studies are limited by their lack of consideration of long-term changes in the ocean carbon cycle, such as the recent possible stalling in the expected growth of the Southern Ocean carbon sink.
Haug, G. H., and Daniel Sigman, 2009: Palaeoceanography: Polar Twins. Nature Geosciences, 2, doi:10.1038/ngeo423 91-92
[ Abstract ]
Ice ages in the North Pacific Ocean and the Southern Ocean were marked by low productivity. Accumulating evidence indicates that strong stratification restricted the supply of nutrients from the deep ocean to the algae of the sunlit surface in these regions.
Henson, S. A., J. P. Dunne, and Jorge Sarmiento, 2009: Decadal variability in North Atlantic phytoplankton blooms. Journal of Geophysical Research, 114(CO403), doi:10.1029/2008JC005139
[ Abstract ]
The interannual to decadal variability in the timing and magnitude of the North Atlantic phytoplankton bloom is examined using a combination of satellite data and output from an ocean biogeochemistry general circulation model. The timing of the bloom as estimated from satellite chlorophyll data is used as a novel metric for validating the model�s skill. Maps of bloom timing reveal that the subtropical bloom begins in winter and progresses northward starting in May in subpolar regions. A transition zone, which experiences substantial interannual variability in bloom timing, separates the two regions. Time series of the modeled decadal (1959�2004) variability in bloom timing show no long-term trend toward earlier or delayed blooms in any of the three regions considered here. However, the timing of the subpolar bloom does show distinct decadal-scale periodicity, which is found to be correlated with the North Atlantic Oscillation (NAO) index. The mechanism underpinning the relationship is identified as anomalous wind-driven mixing conditions associated with the NAO. In positive NAO phases, stronger westerly winds result in deeper mixed layers, delaying the start of the subpolar spring bloom by 2�3 weeks. The subpolar region also expands during positive phases, pushing the transition zone further south in the central North Atlantic. The magnitude of the bloom is found to be only weakly dependent on bloom timing, but is more strongly correlated with mixed layer depth. The extensive interannual variability in the timing of the bloom, particularly in the transition region, is expected to strongly impact the availability of food to higher trophic levels.
Henson, S. A., Jorge Sarmiento, and J. P. Dunne, 2009: Is global warming already changing ocean productivity? Biogeosciences Discuss, www.biogeosciences-discuss.net/6/10311/2009/, 6, 10311-10354
[ Abstract ]
Global warming is predicted to alter the ocean�s biological productivity. But how will we recognise the impacts of climate change on ocean productivity? The most comprehensive information available on the global distribution of ocean productivity comes from satellite 5 ocean colour data. Now that over ten years of SeaWiFS data have accumulated, can we begin to detect and attribute global warming trends in productivity? Here we compare recent trends in SeaWiFS data to longer-term records from three biogeochemical models (GFDL, IPSL and NCAR). We find that detection of real trends in the satellite data is confounded by the relatively short time series and large interannual 10 and decadal variability in productivity. Thus, recent observed changes in chlorophyll, primary production and the size of the oligotrophic gyres cannot be unequivocally attributed to the impact of global warming. Instead, our analyses suggest that a time series of ~40 yr length is needed to distinguish a global warming trend from natural variability. Analysis of modelled chlorophyll and primary production from 2001�2100 15 suggests that, on average, the global warming trend will not be unambiguously separable from decadal variability until ~2055. Because the magnitude of natural variability in chlorophyll and primary production is larger than, or similar to, the global warming trend, a consistent, decades-long data record must be established if the impact of climate change on ocean productivity is to be definitively detected.
Jaccard, S. L., E. D. Galbraith, Daniel Sigman, G. H. Haug, R. Francois, T. F. Pedersen, P. Dulski, and H. R. Thierstein, 2009: Subarctic Pacific evidence for a glacial deepening of the oceanic respired carbon pool. Earth and Planetary Science Letters, 277, doi:10.1016/j.epsl.2008.10.017 156-165
[ Abstract ]
Measurements of benthic foraminiferal cadmium: calcium (Cd/Ca) have indicated that the glacial�interglacial change in deep North Pacific phosphate (PO₄) concentration was minimal, which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redoxsensitive trace metal records from Ocean Drilling Program (ODP) Site 882 (NW subarctic Pacific, water depth 3244 m) to make inferences about changes in deep North Pacific oxygenation � and thus respired carbon storage � over the past 150,000 yr. These observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deepwater oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water mass was depleted in oxygen during glacial maxima, though it was not anoxic. We reconcile our results with the existing benthic foraminiferal Cd/Ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed, rather than remineralized. This change would have corresponded to an increase in the deep Pacific storage of respired carbon, which would have lowered atmospheric carbon dioxide (CO₂) by sequestering CO₂ away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea. The magnitude of change in preformed nutrients suggested by the North Pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pCO₂.
Kopp, Robert E., Frederick J. Simons, Jerry X. Mitrovica, Adam C. Maloof, and Michael Oppenheimer, December 2009: Probabilistic assessment of sea level during the last interglacial stage. Nature, New York, NY, Macmillan, 462, 863-867(17 December 2009), doi:10.1038/nature08686
[ Abstract ]
With polar temperatures ~ 3-5° warmer than today, the last interglacial stage (~125 kyr ago) serves as a partial analogue for 1-2° global warming scenarios. Geological records from several sites indicate that local sea levels during the last interglacial were higher than today, but because local sea levels differ from global sea level, accurately reconstructing past global sea level requires an integrated analysis of globally distributed data sets. Here we present an extensive compilation of local sea level indicators and a statistical approach for estimating global sea level, local sea levels, ice sheet volumes and their associated uncertainties. We find a 95% probability that global sea level peaked at least 6.6m higher than today during the last interglacial; it is likely (67% probability) to have exceeded 8.0m but is unlikely (33% probability) to have exceeded 9.4 m. When global sea level was close to its current level (>10m), the millennial average rate of global sea level rise is very likely to have exceeded 5.6mkyr^-1 but is unlikely to have exceeded 9.2mkyr^-1. Our analysis extends previous last interglacial sea level studies by integrating literature observations within a probabilistic framework that accounts for the physics of sea level change. The results highlight the long-term vulnerability of ice sheets to even relatively low levels of sustained global warming.
Kwon, E. Y., F. Primeau, and Jorge Sarmiento, 2009: The impact of remineralization depth on the air-sea carbon balance. Nature Geosciences, 2, doi:10.1038/ngeo612 630-635
[ Abstract ]
As particulate organic carbon rains down from the surface ocean it is respired back to carbon dioxide and released into the ocean's interior. The depth at which this sinking carbon is converted back to carbon dioxide�known as the remineralization depth�depends on the balance between particle sinking speeds and their rate of decay. A host of climate-sensitive factors can affect this balance, including temperature, oxygen concentration, stratification, community composition and the mineral content of the sinking particles. Here we use a three-dimensional global ocean biogeochemistry model to show that a modest change in remineralization depth can have a substantial impact on atmospheric carbon dioxide concentrations. For example, when the depth at which 63% of sinking carbon is respired increases by 24 m globally, atmospheric carbon dioxide concentrations fall by 10�27 ppm. This reduction in atmospheric carbon dioxide concentration results from the redistribution of remineralized carbon from intermediate waters to bottom waters. As a consequence of the reduced concentration of respired carbon in upper ocean waters, atmospheric carbon dioxide is preferentially stored in newly formed North Atlantic Deep Water. We suggest that atmospheric carbon dioxide concentrations are highly sensitive to the potential changes in remineralization depth that may be caused by climate change.
Le Qu�r�, Corinne, Michael R. Raupach, Josep G. Canadell, Gregg Marland, , Philippe Ciais, Thomas J. Conway, Scott C. Doney, Richard A. Feely, Pru Foster, Pierre Friedlingstein, Kevin Gurney, and Jorge Sarmiento, et al., November 2009: Trends in the Sources and Sinks of Carbon Dioxide In , Nature Geoscience, (Nov. 17, 2009), doi:10.1038/ngeo689
[ Abstract ]
Efforts to control climate change require the stabilization of atmospheric CO₂ concentrations. This can only be achieved through a drastic reduction of global CO₂ emissions. Yet fossil fuel emissions increased by 29% between 2000 and 2008, in conjunction with increased contributions from emerging economies, from the production and international trade of goods and services, and from the use of coal as a fuel source. In contrast, emissions from land-use changes were nearly constant. Between 1959 and 2008, 43% of each year's CO₂ emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO₂ emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a decrease in the uptake of CO₂ by the carbon sinks in response to climate change and variability. Changes in the CO₂ sinks are highly uncertain, but they could have a significant influence on future atmospheric CO₂ levels. It is therefore crucial to reduce the uncertainties.
Lichstein, J W., C. Wirth, H. S. Horn, and Stephen W. Pacala, 2009: Biomass Chronosequences of United States Forests: Implications for Carbon Storage and Forest Management. Old-growth forests, 207, doi:10.1007/978-3-540-92706-8_14 301-341
[ Abstract ]
A variety of mechanisms have been identified that may result in late-successional declines in forest biomass, including synchronous mortality of even-aged early-successional cohorts, increased susceptibility of mature forests to wind or insect damage, and, in some systems, reduced stature of late-successional species. We used data from the United States (US) Forest Service�s Forest Inventory and Analysis (FIA) program, and a literature database on old-growth biomass, to quantify late-successional biomass trajectories in different US forest types. Our results suggest that late-successional biomass declines are rare in US forests. Thus, in most cases, there is no conflict between maximizing carbon storage in forest biomass and protecting or restoring old-growth forests.
Ogle, Kiona, and Stephen W. Pacala, 2009: A modeling framework for inferring tree growth and allocation from physiological, morphological, and allometric traits. Tree Physiology, 29, doi:10.1093/treephys/tpn051 587-605
[ Abstract ]
Predictions of forest succession, diversity and function require an understanding of how species differ in their growth, allocation patterns and susceptibility to mortality. These processes in turn are affected by allometric constraints and the physiological state of the tree, both of which are coupled to the tree�s labile carbon status. Ultimately, insight into the hidden labile pools and the processes affecting the allocation of labile carbon to storage, maintenance and growth will improve our ability to predict tree growth, mortality and forest dynamics. We developed the �Allometrically Constrained Growth and Carbon Allocation� (ACGCA) model that explicitly couples tree growth, mortality, allometries and labile carbon. This coupling results in (1) a semi-mechanistic basis for predicting tree death, (2) an allocation scheme that simultaneously satisfies allometric relationships and physiology- based carbon dynamics and (3) a range of physiological states that are consistent with tree behavior (e.g., healthy, static, shrinking, recovering, recovered and dead). We present the ACGCA model and illustrate aspects of its behavior by conducting simulations under different forest gap dynamics scenarios and with parameter values obtained for two ecologically dissimilar species: loblolly pine (Pinus taeda L.) and red maple (Acer rubrum L.). The model reproduces growth and mortality patterns of these species that are consistent with their shade-tolerance and succession status. The ACGCA framework provides an alternative, and potentially improved, approach for predicting tree growth, mortality and forest dynamics. Keywords: Acer rubrum, carbon allocation, carbon reserves, carbon storage, growth model, labile carbon, loblolly pine, Pinus taeda, red maple, retranslocation, shade-tolerance, succession, tree mortality.
Peters, Catherine A., George Scherer, Michael Celia, Jean Hervé Prévost, T. C. Onstott, P. F. Dobson, C. M Oldenburg, B. Freifeld, J. Birkholzer, J. Wang, S. Benson, and T. J. Phelps, et al., in press: Collaborative Research: DUSEL CO₂, A Deep Underground Laboratory for Geologic CO₂ Sequestration Studies: A proposal for the conceptual design of the facility and experiments. NSF. 0/09.
[ Abstract ]
Princeton University and Lawrence Berkeley National Laboratory have forged a new collaboration to examine the feasibility and risks of carbon sequestration, a method of countering global warming by storing greenhouse gases deep underground. To develop a sound understanding of carbon sequestration, we will build a deep underground laboratory to study the processes of trapping and storing CO₂, including the risks of unintended leakage. It will be part of the new DUSEL facility at the Homestake mine in South Dakota. The �DUSEL CO₂, facility will make the United States the only country with a deep underground laboratory for controlled study of geologic carbon sequestration, providing a unique opportunity for global leadership. The findings from these unique experiments will advance carbon management technology worldwide and help reduce global greenhouse gas emissions. The features and capabilities of the planned facility are unprecedented. The experimental design exploits the nearly half-kilometer vertical extent of existing �sandline� borings at Homestake. Pipes will be installed within the sandlines to serve as long flow columns. These columns will contain the CO₂, and allow experimentation at the same pressure and temperature conditions as in deep subsurface reservoirs. Fill materials will mimic sedimentary layering, as well as cements in plugged wells. Instrumentation will enable detailed monitoring of flow, pressure, temperature, brine composition, geomechanics, and microbial activity. As part of the initial suite of experiments, we plan to simulate a leak in which CO₂, changes from a supercritical fluid to a subcritical gas as the pressure drops during upflow over tens to hundreds of meters. We will test for possible acceleration in CO₂, flow due to increasing buoyancy. Also, we will examine the interactions of CO₂, with cap-rocks and well cements, and determine whether CO₂, will enlarge flow pathways or cause selfsealing. Finally, we will investigate the effects of anaerobic, thermophilic bacteria on CO₂, conversion to methane and carbonate. This project is being led by researchers at Princeton and LBNL, and involves no-cost collaboration with individuals at ORNL, Stanford University, Schlumberger and the U.S. DOE NETL. During this three-year project, the team is working to (i) prioritize future experiments that will be conducted at DUSEL CO₂, (ii) build models that simulate experimental conditions and predict process dynamics, and (iii) develop a Work-Breakdown Structure (WBS) schedule for design, procurement, construction, operation and deconstruction of the facility over the facility lifetime. International awareness about DUSEL CO₂, is being fostered through international workshops and formation of an International Advisory Committee. Also, we are collaborating with other DUSEL scientists on education and outreach about �deep science,� with particular focus on climate change and energy solutions. DUSEL education and outreach activities are focused on Native American communities in South Dakota and operation of the Visitor Center at the Sanford Lab at Homestake. To inspire and educate the next generation of leaders, we are involving undergraduate and graduate students in DUSEL CO₂, research at Princeton University.
Ren, H., Daniel Sigman, , B. Plessen, R. S. Robinson, Y. Rosenthal, and G. H. Haug, 2009: Foraminiferal isotope evidence of reduced nitrogen fixation in the ice age Atlantic Ocean. Science, 323, doi:10.1126/science.1165787 244-248
[ Abstract ]
Fixed nitrogen (N) is a limiting nutrient for algae in the low-latitude ocean, and its oceanic inventory may have been higher during ice ages, thus helping to lower atmospheric CO₂ during those intervals. In organic matter within planktonic foraminifera shells in Caribbean Sea sediments, we found that the ¹⁵N/¹⁴N ratio from the last ice age is higher than that from the current interglacial, indicating a higher nitrate ¹⁵N/¹⁴N ratio in the Caribbean thermocline. This change and other species-specific differences are best explained by less N fixation in the Atlantic during the last ice age. The fixation decrease was most likely a response to a known ice age reduction in ocean N loss, and it would have worked to balance the ocean N budget and to curb ice age�interglacial change in the N inventory.
Rodgers, K. B., R. M. Key, A. Gnanadesikan, Jorge Sarmiento, O. Aumont, L. Bopp, S. C. Doney, J. P. Dunne, D. M. Glover, A. Ishida, M. Ishii, and A. R. Jacobson, et al., 2009: Using altimetry to help explain patchy changes in hydrographic carbon measurements. Journal of Geophysical Research � Oceans, doi:10.1029/2008JC005183 114
[ Abstract ]
Here we use observations and ocean models to identify mechanisms driving large seasonal to interannual variations in dissolved inorganic carbon (DIC) and dissolved oxygen (O₂) in the upper ocean. We begin with observations linking variations in upper ocean DIC and O₂ inventories with changes in the physical state of the ocean. Models are subsequently used to address the extent to which the relationships derived from short-timescale (six months to two years) repeat measurements are representative of variations over larger spatial and temporal scales. The main new result is that convergence and divergence (column stretching) attributed to baroclinic Rossby waves can make a first-order contribution to DIC and O₂ variability in the upper ocean. This results in a close correspondence between natural variations in DIC and O₂ column inventory variations and sea surface height (SSH) variations over much of the ocean. Oceanic Rossby wave activity is an intrinsic part of the natural variability in the climate system and is elevated even in the absence of significant interannual variability in climate mode indices. The close correspondence between SSH and both DIC and O₂ column inventories for many regions suggests that SSH changes (inferred from satellite altimetry) may prove useful in reducing uncertainty in separating natural and anthropogenic DIC signals (using measurements from CLIVAR�s CO₂/Repeat Hydrography program).
Sarmiento, Jorge, M. N. Gloor, N. Gruber, C. Beaulieu, A. R. Jacobson, S. M. Fletcher, Stephen W. Pacala, and K. B. Rodgers, 2009: Trends and Regional Distributions of Land and Ocean Carbon Sink. Biogeosciences, http://www.biogeosciences-discuss.net/6/10583/2009/bgd-6-10583-2009.html, (6), 10583-10624
[ Abstract ]
We show here a new estimate of the variability and long-term trends in the net land carbon sink from 1960 onwards calculated from the difference between fossil fuel emissions, the observed atmospheric growth rate, and the ocean uptake obtained by 5 recent ocean model simulations forced with reanalysis wind stress and heat and water fluxes. The net land carbon sink appears to have increased by −0.88 (−0.77 to −1.04) PgCyr−1 after 1988/1989 from a relatively constant mean of −0.27 PgCyr−1 before then to −1.15 PgCyr−1 thereafter (the sign convention is negative out of the atmosphere). This result is significant at the 1% critical level. The increase in net land 10 uptake is partially compensated by a reduction in the expected oceanic uptake, which we estimate from model simulations as about 0.35 (0.26 to 0.49) PgCyr−1. This implies that the atmospheric growth rate must have decreased by about −0.53 (−0.51 to −0.55) PgCyr−1 (equivalent to −0.25 ppm yr−1) below what would have been projected if the ocean uptake had continued to grow at the rate expected from a constant 15 climate model and if the net land uptake had continued at its pre-1988/1989 level. A regional synthesis and assessment of the land carbon sources and sinks over the post 1988/1989 period reveals broad agreement that the northern hemisphere land is a major sink of atmospheric CO2, but there remain major discrepancies with regard to the sign and magnitude of the net flux to and from tropical land.
Sarmiento, Jorge, R. D. Slater, J. P. Dunne, A. Gnanadesikan, and M. R. Hiscock, 2009: Efficiency of Small Scale Carbon Mitigation by Patch Iron Fertilization. Biogeosciences, http://www.biogeosciences-discuss.net/6/10381/2009/bgd-6-10381-2009.html, (6), 10381-10446
[ Abstract ]
While nutrient depletion scenarios have long shown that the high-latitude High Nutrient Low Chlorophyll (HNLC) regions are the most effective for sequestering atmospheric carbon dioxide, recent simulations with prognostic biogeochemical models have suggested that only a fraction of the potential drawdown can be realized. We use a global ocean biogeochemical general circulation model developed at GFDL and Princeton to examine this and related issues. We fertilize two patches in the North and Equatorial Pacific, and two additional patches in the Southern Ocean HNLC region north of the biogeochemical divide and in the Ross Sea south of the biogeochemical divide. We obtain by far the greatest response to iron fertilization at the Ross Sea site. Here the CO2 remains sequestered on century time-scales and the efficiency of fertilization remains almost constant no matter how frequently iron is applied as long as it is confined to the growing season. The second most efficient site is in the Southern Ocean. Here the biological response to iron fertilization is comparable to the Ross Sea, but the enhanced biological uptake of CO2 is more spread out in the vertical and thus less effective at leading to removal of CO2 from the atmosphere. The North Pacific site has lower initial nutrients and thus a lower efficiency. Fertilization of the Equatorial Pacific leads to an expansion of the suboxic zone and a striking increase in denitrification that causes a sharp reduction in overall surface biological export production and CO2 uptake. The impacts on the oxygen distribution and surface biological export are less prominent at other sites, but nevertheless still a source of concern. The century time scale retention of iron in these models greatly increases the long-term biological response to iron addition as compared with models in which the added iron is rapidly scavenged from the ocean.
Searchinger, Timothy, Steven P. Hamburg, J. M. Melillo, W. Chameides, Petr Havlik, Daniel M. Kammen, Gene E. Likens, Ruben N. Lubowski, M. Obersteiner, Michael Oppenheimer, G. Philip Robertson, William H. Schlesinger, and G. David Tilman, October 2009: Fixing a Critical Climate Accounting Error. Science, Washington, D.C., American Association for the Advancement of Science, 326(5952), doi:10.1126/science.1178797 527-528
[ Abstract ]
The accounting now used for assessing compliance with carbon limits in the Kyoto Protocol and in climate legislation contains a far-reaching but fixable flaw that will severely undermine greenhouse gas reduction goals (1). It does not count CO₂ emitted from tailpipes and smokestacks when bioenergy is being used, but it also does not count changes in emissions from land use when biomass for energy is harvested or grown. This accounting erroneously treats all bioenergy as carbon neutral regardless of the source of the biomass, which may cause large differences in net emissions. For example, the clearing of long-established forests to burn wood or to grow energy crops is counted as a 100% reduction in energy emissions despite causing large releases of carbon.
Shapiro, H. T., M. S. Wrighton, J. F. Ahearne, A. J. Bard, J. Beyea, William F. Brinkman, D. M. Chapin, S. Chu, C. A. Ehlig-Economides, R. W. Fri, C. H. Goodman, J. B. Heywood, L. B. Lave, J. J. Markowsky, R. A. Meserve, W. F. Miller Jr., F. M. Orr, Jr., L. T. Papay, A.A.N. Patrinos, M. P. Ramage, M. L. Savitz, Robert H. Socolow, J. L. Sweeney, G. D. Tilman, and C. Walton, 2009: America's Energy Future: Technology and Transformation. Committee on America's Energy Future, National Research Council of the National Academies,, Washington, D.C., The National Academies Press, (ISBN-10: 0-309-14141),
[ Abstract ]
To stimulate and inform a constructive national dialogue about our energy future, the National Academy of Sciences and the National Academy of Engineering initiated in 2007 a major study, "America's Energy Future: Technology Opportunities, Risks, and Tradeoffs." The America's Energy Future (AEF) project was initiated in anticipation of major legislative interest in energy policy in the U.S. Congress and, as the effort proceeded, it was endorsed by Senate Energy and Natural Resources Committee Chair Jeff Bingaman and former Ranking Member Pete Domenici.
The AEF project evaluates current contributions and the likely future impacts, including estimated costs, of existing and new energy technologies. It was planned to serve as a foundation for subsequent policy studies, at the Academies and elsewhere, that will focus on energy research and development priorities, strategic energy technology development, and policy analysis.
The AEF project has produced a series of five reports, including this report, designed to inform key decisions as the nation begins this year a comprehensive examination of energy policy issues. Numerous studies conducted by diverse organizations have benefited the project, but many of those studies disagree about the potential of specific technologies, particularly those involving alternative sources of energy such as biomass, renewable resources for generation of electric power, advanced processes for generation from coal, and nuclear power. A key objective of the AEF series of reports is thus to help resolve conflicting analyses and to facilitate the charting of a new direction in the nation's energy enterprise.
The AEF project, outlined in Appendix B, included a study committee and three panels that together have produced an extensive analysis of energy technology options for consideration in an ongoing national dialogue. A milestone in the project was the March 2008 "National Academies Summit on America's Energy Future" at which principals of related recent studies provided input to the AEF study committee and helped to inform the panels' deliberations. A report chronicling the event, The National Academies Summit on America's Energy Future: Summary of a Meeting, was published in October 2008.
Shevliakova, E., Stephen W. Pacala, S. Malyshev, G. C. Hurtt, P.C.D. Milly, J. P. Caspersen, L. T. Sentman, J. P. Fisk, C. Wirth, and C. Crevoisier, 2009: Carbon Cycling Under 300 Years of Land-Use Change: The Importance of the Secondary Vegetation Sink. Global Biogeochemical Cycles, doi:10.1029/2007GB003176
[ Abstract ]
We have developed a dynamic land model (LM3V) able to simulate ecosystem dynamics and exchanges of water, energy, and CO₂ between land and atmosphere. LM3V is specifically designed to address the consequences of land use and land management changes including cropland and pasture dynamics, shifting cultivation, logging, fire, and resulting patterns of secondary regrowth. Here we analyze the behavior of LM3V, forced with the output from the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model AM2, observed precipitation data, and four historic scenarios of land use change for 1700�2000. Our analysis suggests a net terrestrial carbon source due to land use activities from 1.1 to 1.3 GtC/a during the 1990s, where the range is due to the difference in the historic cropland distribution. This magnitude is substantially smaller than previous estimates from other models, largely due to our estimates of a secondary vegetation sink of 0.35 to 0.6 GtC/a in the 1990s and decelerating agricultural land clearing since the 1960s. For the 1990s, our estimates for the pastures� carbon flux vary from a source of 0.37 to a sink of 0.15 GtC/a, and for the croplands our model shows a carbon source of 0.6 to 0.9 GtC/a. Our process-based model suggests a smaller net deforestation source than earlier bookkeeping models because it accounts for decelerated net conversion of primary forest to agriculture and for stronger secondary vegetation regrowth in tropical regions. The overall uncertainty is likely to be higher than the range reported here because of uncertainty in the biomass recovery under changing ambient conditions, including atmospheric CO₂ concentration, nutrients availability, and climate.
Shi, Dalin, Yan Xu, and Francois Morel, 2009: Effects of the pH/pCO₂ control method on medium chemistry and phytoplankton growth. Biogeosciences, http://www.biogeosciences.net/6/1199/2009/bg-6-1199-2009.pdf, 6(1199-1207),
[ Abstract ]
The control of key chemical parameters in phytoplankton cultures, such as pCO₂, pH and � (the saturation state of calcium carbonate), is made difficult by the interdependence of these parameters and by the changes resulting from the growth of the organisms, such as andCO₂ fixation, nutrient uptake and, for coccolithophores, calcite precipitation. Even in cultures where pandCO₂ or pH is maintained constant, other chemical parameters change substantially at high cell densities. Experimentally we observed that various methods of adjustment of pandCO₂/pH � acid or base addition, use of buffers or pH-stats, or bubbling of andCO₂-enriched air � can be used, the choice of one or the other depending on the goals of the experiments. At seawater pH, we measured the same growth rates in cultures of the diatom Thalassiosira weissflogii where the pandCO₂/pH was controlled by these different methods. The pH/pandCO₂control method also did not affect the rates of growth or calcification of the coccolithophore Emiliania huxleyi at seawater pH. At lower pH/higher pandCO₂, in the E. huxleyi strain PLY M219, we observed increases in rates of carbon fixation and calcification per cell, along with a slight increase in growth rate, except in bubbled cultures. In our hands, the bubbling of cultures seemed to induce more variable results than other methods of pandCO₂/pH control. While highly convenient, the addition of pH buffers to the medium apparently induces changes in trace metal availability and cannot be used under trace metal-limiting conditions.
Sigman, Daniel, P. J. DiFiore, M. P. Hain, C. Deutsch, and D. Karl, 2009: Sinking organic matter spreads the nitrogen isotope signal of pelagic denitrification in the North Pacific. Geophysical Research Letters, 36(L08605), doi:10.1029/2008GL035784
[ Abstract ]
Culture studies of denitrifying bacteria predict that denitrification will generate equivalent gradients in the δ¹⁵N and &delta:¹⁸O of deep ocean nitrate. A depth profile of nitrate isotopes from the Hawaii Ocean Time-series Station ALOHA shows less of an increase in &delta:¹⁸O than in δ¹⁵N as one ascends from abyssal waters into the denitrification impacted mid-depth waters. A box model of the ocean nitrate N and O isotopes indicates that this is the effect of the low latitude nitrate assimilation/regeneration cycle: organic N sinking out of the surface spreads the high -δ¹⁵N signal of pelagic denitrification into waters well below and beyond the suboxic zone, whereas the nitrate &delta:¹⁸O signal of denitrification can only be transmitted by circulation in the interior.
Sigman, Daniel, P. J. DiFiore, M. P. Hain, C. Deutsch, Y. Wang, D. Karl, T. R. Knutson, K. K. Lehman, and S. Pantoja, 2009: The dual isotopes of deep nitrate as a constraint on the cycle and budget of oceanic fixed nitrogen. Deep Sea Research I, 56(9), doi:10.1016/j.dsr.2009.04.007 1419-1439
[ Abstract ]
We compare the output of an 18-box geochemical model of the ocean with measurements to investigate the controls on both the mean values and variation of nitrate δ¹⁵N and &delta:¹⁸O in the ocean interior. The &delta:¹⁸O of nitrate is our focus because it has been explored less in previous work. Denitrification raises the δ¹⁵N and &delta:¹⁸O of mean ocean nitrate by equal amounts above their input values for N₂ fixation (for δ¹⁵N) and nitrification (for &delta:¹⁸O), generating parallel gradients in the δ¹⁵N and &delta:¹⁸O of deep ocean nitrate. Partial nitrate assimilation in the photic zone also causes equivalent increases in the δ¹⁵N and &delta:¹⁸O of the residual nitrate that can be transported into the interior. However, the regeneration and nitrification of sinking N can be said to decouple the N and O isotopes of deep ocean nitrate, especially when the sinking N is produced in a low latitude region, where nitrate consumption is effectively complete. The δ¹⁵N of the regenerated nitrate is equivalent to that originally consumed, whereas the regeneration replaces nitrate previously elevated in &delta:¹⁸O due to denitrification or nitrate assimilation with nitrate having the &delta:¹⁸O of nitrification. This lowers the &delta:¹⁸O of mean ocean nitrate and weakens nitrate &delta:¹⁸O gradients in the interior relative to those in δ¹⁵N. This decoupling is characterized and quantified in the box model, and agreement with data shows its clear importance in the real ocean. At the same time, the model appears to generate overly strong gradients in both &delta:¹⁸O and δ¹⁵N within the ocean interior and a mean ocean nitrate &delta:¹⁸O that is higher than measured. This may be due to, in the model, too strong an impact of partial nitrate assimilation in the Southern Ocean on the δ¹⁵N and &delta:¹⁸O of preformed nitrate and/or too little cycling of intermediate-depth nitrate through the low latitude photic zone.
Smith, D., A. C. Schuerger, M. Davidson, Stephen W. Pacala, C. Bakermans, and T. C. Onstott, 2009: Survivability of Psychrobacter Cryohalolentis K5 Under Simulated Martian Surface Conditions. Astrobiology, 9(2), doi:10.1089/ast.2007.0231 221-228
[ Abstract ]
Spacecraft launched to Mars can retain viable terrestrial microorganisms on board that may survive the interplanetary transit. Such biota might compromise the search for life beyond Earth if capable of propagating on Mars. The current study explored the survivability of Psychrobacter cryohalolentis K5, a psychrotolerant microorganism obtained from a Siberian permafrost cryopeg, under simulated martian surface conditions of high ultraviolet irradiation, high desiccation, low temperature, and low atmospheric pressure. First, a desiccation experiment compared the survival of P. cryohalolentis cells embedded, or not embedded, within a medium/salt matrix (MSM) maintained at 25�C for 24 h within a laminar flow hood. Results indicate that the presence of the MSM enhanced survival of the bacterial cells by 1 to 3 orders of magnitude. Second, tests were conducted in a Mars Simulation Chamber to determine the UV tolerance of the microorganism. No viable vegetative cells of P. cryohalolentis were detected after 8 h of exposure to Mars-normal conditions of 4.55 W/m2 UVC irradiation (200�280 nm), −12.5�C, 7.1 mbar, and a Mars gas mix composed of CO2 (95.3%), N2 (2.7%), Ar (1.6%), O2 (0.2%), and H2O (0.03%). Third, an experiment was conducted within the Mars chamber in which total atmospheric opacities were simulated at � = 0.1 (dust-free CO2 atmosphere at 7.1 mbar), 0.5 (normal clear sky with 0.4 = dust opacity and 0.1 = CO2-only opacity), and 3.5 (global dust storm) to determine the survivability of P. cryohalolentis to partially shielded UVC radiation. The survivability of the bacterium increased with the level of UVC attenuation, though population levels still declined several orders of magnitude compared to UVC-absent controls over an 8 h exposure period.
Socolow, Robert H., and Alexander Glaser, September 2009: Balancing risks: nuclear energy & climate change. Dædalus, Cambridge, MA, MIT Press for the American Academy of Arts & Sciences, 138(4), doi:10.1162/daed.2009.138.4.31 31-44
[ Abstract ]
Nuclear power could make a significant contribution to climate change mitigation. To do so, however, nuclear power must be deployed extensively in many developing countries that increasingly share production and consumption patterns with the industrialized world. Some of these countries are politically unstable today. If nuclear power is sufficiently unattractive in such a deployment scenario, nuclear power is not on the list of solutions to climate change.

Nuclear power will not benefit climate change if its contribution is withdrawn a decade or two after global scale-up begins, as a result of the coupling of nuclear power to nuclear weapons. The coupling of nuclear power to nuclear weapons is the most critical flaw of nuclear power today and is the result of nuclear power's inadequate system of international governance and its reliance on uranium enrichment plants and reprocessing plants under national control.

A world considerably safer for nuclear power could emerge as a co- benefit of the nuclear disarmament process. A multilateral nuclear disarmament process might be the most effective way-perhaps the only way-for states to decouple nuclear power from nuclear weapons.

The next decade is critical. It can used to establish international ownership of uranium enrichment, the cessation of all spent fuel reprocessing, and much more effective norms of international governance.

Every "solution" to climate change can be done badly or well. Done badly, solutions can be worse than the disease. Making climate change the world's exclusive priority is therefore dangerous. Conceding that such conclusions can embody only the most subjective of considerations, we judge the hazard of aggressively pursuing a global expansion of nuclear power today to be worse than the hazard of slowing the attack on climate change by whatever increment such caution entails. If over the next decade the world demonstrates that it can do nuclear power well, a global expansion of nuclear power would have to be -- indeed, should be -- seriously reexamined.
Tilman, D., Robert H. Socolow, J. A. Foley, J. Hill, Eric Larson, L. R. Lynd, Stephen W. Pacala, J. Reilly, Timothy Searchinger, C. Sommerville, and Robert H. Williams, July 2009: Beneficial Biofuels - The Food, Energy, and Environment Trilemma. Science, Washington, D.C., American Association for the Advancement of Science, 325(5938), doi:10.1126/science.1177970 270-271
[ Abstract ]
Exploiting multiple feedstocks, under new policies and accounting rules, to balance biofuel production, food security, and greenhouse-gas reduction.
Dramatic improvements in policy and technology are needed to meet global demand for both food and biofuel feedstocks.
Tol, R.S.J., Robert H. Socolow, and Stephen W. Pacala, 2009: Understanding Long-Term Energy Use and Carbon Dioxide Emissions in the USA. Journal of Policy Modeling, 31, doi:10.1016/j.jpolmod.2008.12.002 425-445
[ Abstract ]
Energy is at the core of some of the greatest environmental and geopolitical challenges of our time. Cheap and plentiful energy � deemed necessary for our current standard of living � can at the moment only be supported by oil and coal, which pollutes the air, changes the climate, and, in the case of oil and gas, comes from unstable regions. Besides stimulating less polluting energy sources, it is important to improve the overall energy efficiency of the economy through technological, behavioural and other changes. For that, one needs to understand how and why energy use has changed in the past. This paper contributes to that.
Xu, Y., Robert H. Williams, and Robert H. Socolow, 2009: China�s rapid deployment of SO₂ scrubbers. Energy and Environmental Science, 2, doi:10.1039/B901357C 459-465
[ Abstract ]
Details are gradually emerging regarding China�s extraordinary commitment to environmental technology that began in 2006. With the help of Chinese written references and some field verification, we tell here the story of the rapid deployment of sulfur dioxide scrubbers at coal power plants in 2006 and 2007. Scrubbers were installed in each of these years at plants with more than 100 000 megawatts of total generating capacity, overtaking the rate of construction of new coal power plants. Scrubber installation in each year equaled the entire scrubber capacity in the U.S. We also describe novel policies enacted by China in 2007 to increase the likelihood that installed scrubbers actually operate.
Xu, Y., J. M. Boucher, and Francois Morel, 2009: Expression and Diversity of Alkaline Phosphatase EHAP1 in Emiliania Huxleyi (Prymnesiophyceae). Journal of Phycology, 46(1), doi:10.1111/j.1529-8817.2009.00788.x 85-92
[ Abstract ]
Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler is a cosmopolitan coccolithophore species that forms massive blooms in low phosphorus seawater, partly due to its ability to utilize organic phosphate via extracellular alkaline phosphatase (AP). A novel AP gene, ehap1, was identified from the strain CCMP374. In this study, we examined the expression of ehap1 in various E. huxleyi strains and its genetic diversity in those strains and field populations. Two EHAP1 proteins (EHAP1a, 75 kDa and EHAP1b, 110 kDa) with virtually identical sequence were expressed under P limitation in all strains except one; a third protein (EHAP1c, 115 kDa) was expressed in a few strains. The correlation between AP activity and protein abundance suggests that EHAP1b is inactive and probably the precursor of EHAP1a. The transcript of ehap1 was induced by P depletion in all strains. The ehap1 gene sequence is highly conserved in these strains and field populations with <3% nucleic acid substitution. Most of the ehap1 sequences from one site in the English Channel and three sites in the Gulf of Alaska were essentially identical to one another. No EHAP1-like protein can be detected in other phytoplankton species tested via Western blot analysis. The rapid induction and high activity of EHAP1 in E. huxleyi suggest that it plays a significant role in P regeneration in the oligotrophic ocean where E. huxleyi is abundant. The EHAP1 antibody and gene-specific primers are well suited to study the dynamics of P limitation in field populations of E. huxleyi.
Bender, Michael, B. Barnett, G. Dreyfus, J. Jouzel, and D. Porcelli, 2008: The contemporary degassing rate of ⁴⁰Ar from the solid Earth. Proceedings of the National Academy of Sciences of the United States of America, 105(24), doi:10.1073/pnas.0711679105
[ Abstract ]
Knowledge of the outgassing history of radiogenic ⁴⁰Ar, derived over geologic time from the radioactive decay of ⁴⁰K, contributes to our understanding of the geodynamic history of the planet and the origin of volatiles on Earth�s surface. The ⁴⁰Ar inventory of the atmosphere equals total ⁴⁰Ar outgassing during Earth history. Here, we report the current rate of ⁴⁰Ar outgassing, accessed by measuring the Ar isotope composition of trapped gases in samples of the Vostok and Dome C deep ice cores dating back to almost 800 ka. The modern outgassing rate (1.1 � 0.1 x 10⁸ mol/yr) is in the range of values expected by summing outgassing from the continental crust and the upper mantle, as estimated from simple calculations and models. The measured outgassing rate is also of interest because it allows dating of air trapped in ancient ice core samples of unknown age, although uncertainties are large (�180 kyr for a single sample or �11% of the calculated age, whichever is greater).
Brauer, A., G. H. Haug, P. Dulski, Daniel Sigman, and F. W. Negendank, 2008: An abrupt wind shift in Western Europe at the onset of the Younger Dryas cold period. Nature Geosciences, 1, doi:10.1038/ngeo263 520-523
[ Abstract ]
The Younger Dryas cooling 12,700 years ago is one of the most abrupt climate changes observed in Northern Hemisphere palaeoclimate records. Annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes, as the seasonal deposition responds immediately to climate, and the varve counts provide an accurate estimate of the timing of the change. Here, we present sub-annual records of varve microfacies and geochemistry from Lake Meerfelder Maar in western Germany, providing one of the best dated records of this climate transition. Our data indicate an abrupt increase in storminess during the autumn to spring seasons, occurring from one year to the next at 12,679 yr BP, broadly coincidentwith other changes in this region. We suggest that this shift in wind strength represents an abrupt change in the North Atlantic westerlies towards a stronger and more zonal jet. Changes in meridional overturning circulation alone cannot fully explain the changes in European climate; we suggest the observed wind shift provides the mechanism for the strong temporal link between North Atlantic Ocean overturning circulation and European climate during deglaciation.
Cassar, N., G. McKinley, Michael Bender, R. Mika, and M. Battle, 2008: An improved comparison of atmospheric Ar/N₂ time series and paired ocean-atmosphere model predictions. Journal of Geophysical Research � Atmosphere, 113(D21122), doi:10.1029/2008JD009817
[ Abstract ]
Ar/N₂ variations in the atmosphere reflect ocean heat fluxes, air-sea gas exchange, and atmospheric dynamics. Here atmospheric Ar/N₂ time series are compared to paired ocean-atmosphere model predictions. Agreement between Ar/N₂ observations and simulations has improved in comparison to a previous study because of longer time series and the introduction of automated samplers at several of the atmospheric stations, as well as the refinement of the paired ocean-atmosphere models by inclusion of Ar and N₂ as active tracers in the ocean component. Although analytical uncertainties and collection artifacts are likely to be mainly responsible for observed Ar/N₂ outliers, air parcel back-trajectory analysis suggests that some of the variability in Ar/N₂ measurements could be due to the low-altitude history of the air mass collected and, by extension, the local oceanic Ar/N₂ signal. Although the simulated climatological seasonal cycle can currently be evaluated with Ar/N₂ observations, longer time series and additional improvements in the signal-to-noise ratio will be required to test other model predictions such as interannual variability, latitudinal gradients, and the secular increase in atmospheric Ar/N₂ expected to result from ocean warming.
Crutzen, P., and Michael Oppenheimer, 2008: Learning about ozone depletion. Climatic Change, 89(1-2), doi:10.1007/S10584-008-9400-6 143-154
[ Abstract ]
Stratospheric ozone depletion has been much studied as a case history in the interaction between environmental science and environmental policy. The positive influence of science on policy is often underscored, but here we review the photochemistry of ozone in order to illustrate how scientific learning has the potential to mislead policy makers. The latter may occur particularly in circumstances where limited observations are combined with simplified models of a complex system, such as may generally occur in the global change arena. Even for the well-studied case of ozone depletion, further research is needed on the dynamics of scientific learning, particularly the scientific assessment process, and how assessments influence the development of public policy.
de Boer, A. M., J. R. Toggweiler, and Daniel Sigman, 2008: Atlantic dominance of the meridional overturning circulation. Journal of Physical Oceanography, 38, doi:10.1175/2007JPO3731.1 435-450
[ Abstract ]
North Atlantic (NA) deep-water formation and the resulting Atlantic meridional overturning cell is generally regarded as the primary feature of the global overturning circulation and is believed to be a result of the geometry of the continents. Here, instead, the overturning is viewed as a global energy�driven system and the robustness of NA dominance is investigated within this framework. Using an idealized geometry ocean general circulation model coupled to an energy moisture balance model, various climatic forcings are tested for their effect on the strength and structure of the overturning circulation. Without winds or a high vertical diffusivity, the ocean does not support deep convection. A supply of mechanical energy through winds or mixing (purposefully included or due to numerical diffusion) starts the deep-water formation. Once deep convection and overturning set in, the distribution of convection centers is determined by the relative strength of the thermal and haline buoyancy forcing. In the most thermally dominant state (i.e., negligible salinity gradients), strong convection is shared among the NA, North Pacific (NP), and Southern Ocean (SO), while near the haline limit, convection is restricted to the NA. The effect of a more vigorous hydrological cycle is to produce stronger salinity gradients, favoring the haline state of NA dominance. In contrast, a higher mean ocean temperature will increase the importance of temperature gradients because the thermal expansion coefficient is higher in a warm ocean, leading to the thermally dominated state. An increase in SO winds or global winds tends to weaken the salinity gradients, also pushing the ocean to the thermal state. Paleoobservations of more distributed sinking in warmer climates in the past suggest that mean ocean temperature and winds play a more important role than the hydrological cycle in the overturning circulation over long time scales.
Gloor, M. N., N. Gruber, Jorge Sarmiento, C. L. Sabine, R. A. Feely, and C. Rödenbeck, 2008: A first estimate of present and pre-industrial CO₂ flux patterns based on ocean interior carbon measurements and models. Geophysical Research Letters, 30(1), doi:10.1029/2002GL015594
[ Abstract ]
The exchange of CO₂ across the air-sea interface is a main determinant of the distribution of atmospheric CO₂ from which major conclusions about the carbon cycle are drawn, yet our knowledge of atmosphere-ocean fluxes still has major gaps. A new analysis based on recent ocean dissolved inorganic carbon data and on models permits us to separately estimate the preindustrial and present air-sea CO₂ flux distributions without requiring knowledge of the gas exchange coefficient. We find a smaller carbon sink at mid to high latitudes of the southern hemisphere than previous data based estimates and a shift of ocean uptake to lower latitude regions compared to estimates and simulations. The total uptake of anthropogenic CO₂ for 1990 is 1.8 (�0.4) Pg C yr^-1. Our ocean based results support the interpretation of the latitudinal distribution of atmospheric CO₂ data as evidence for a large northern hemisphere land carbon sink.
Levine, N. M., S. C. Doney, R. Wanninkhof, K. Lindsay, and I. Y. Fung, 2008: Impact of ocean carbon system variability on the detection of temporal increases in anthropogenic CO₂. Journal of Geophysical Research, 113(C03019), doi:10.1029/2007JC004153
[ Abstract ]
Estimates of temporal trends in oceanic anthropogenic carbon dioxide (CO₂) rely on the ability of empirical methods to remove the large natural variability of the ocean carbon system. A coupled carbon-climate model is used to evaluate these empirical methods. Both the ΔC* and multiple linear regression (MLR) techniques reproduce the predicted increase in dissolved inorganic carbon for the majority of the ocean and have similar average percent errors for decadal differences (24.1% and 25.5%, respectively). However, this study identifies several regions where these methods may introduce errors. Of particular note are mode and deep water formation regions, where changes in air-sea disequilibrium and structure in the MLR residuals introduce errors. These results have significant implications for decadal repeat hydrography programs, indicating the need for subannual sampling in certain regions of the oceans in order to better constrain the natural variability in the system and to robustly estimate the intrusion of anthropogenic CO₂.
Marinov, I., A. Gnanadesikan, Jorge Sarmiento, J. R. Toggweiler, M. Follows, and B. K. Mignone, 2008: Impact of oceanic circulation on biological Carbon Storage in the ocean and atmospheric pCO₂. Global Biogeochemical Cycles, 22(GB3007), doi:10.1029/2007GB002958
[ Abstract ]
We use both theory and ocean biogeochemistry models to examine the role of the soft-tissue biological pump in controlling atmospheric CO₂. We demonstrate that atmospheric CO₂ can be simply related to the amount of inorganic carbon stored in the ocean by the soft-tissue pump, which we term (OCSsoft). OCSsoft is linearly related to the inventory of remineralized nutrient, which in turn is just the total nutrient inventory minus the preformed nutrient inventory. In a system where total nutrient is conserved, atmospheric CO₂ can thus be simply related to the global inventory of preformed nutrient. Previous model simulations have explored how changes in the surface concentration of nutrients in deepwater formation regions change the global preformed nutrient inventory. We show that changes in physical forcing such as winds, vertical mixing, and lateral mixing can shift the balance of deepwater formation between the North Atlantic (where preformed nutrients are low) and the Southern Ocean (where they are high). Such changes in physical forcing can thus drive large changes in atmospheric CO₂, even with minimal changes in surface nutrient concentration. If Southern Ocean deepwater formation strengthens, the preformed nutrient inventory and thus atmospheric CO₂ increase. An important consequence of these new insights is that the relationship between surface nutrient concentrations, biological export production, and atmospheric CO₂ is more complex than previously predicted. Contrary to conventional wisdom, we show that OCSsoft can increase and atmospheric CO₂ decrease, while surface nutrients show minimal change and export production decreases.
Marinov, I., M. Follows, A. Gnanadesikan, Jorge Sarmiento, and R. D. Slater, 2008: How does ocean biology affect atmospheric pCO₂: Theory and models. Journal of Geophysical Research, 113(C07032), doi:10.1029/2007JC004598
[ Abstract ]
This paper examines the sensitivity of atmospheric pCO₂ to changes in ocean biology that result in drawdown of nutrients at the ocean surface. We show that the global inventory of preformed nutrients is the key determinant of atmospheric pCO₂ and the oceanic carbon storage due to the soft-tissue pump (OCSsoft). We develop a new theory showing that under conditions of perfect equilibrium between atmosphere and ocean, atmospheric pCO₂ can be written as a sum of exponential functions of OCSsoft. The theory also demonstrates how the sensitivity of atmospheric pCO₂ to changes in the soft-tissue pump depends on the preformed nutrient inventory and on surface buffer chemistry. We validate our theory against simulations of nutrient depletion in a suite of realistic general circulation models (GCMs). The decrease in atmospheric pCO₂ following surface nutrient depletion depends on the oceanic circulation in the models. Increasing deep ocean ventilation by increasing vertical mixing or Southern Ocean winds increases the atmospheric pCO₂ sensitivity to surface nutrient forcing. Conversely, stratifying the Southern Ocean decreases the atmospheric CO₂ sensitivity to surface nutrient depletion. Surface CO₂ disequilibrium due to the slow gas exchange with the atmosphere acts to make atmospheric pCO₂ more sensitive to nutrient depletion in high-ventilation models and less sensitive to nutrient depletion in low-ventilation models. Our findings have potentially important implications for both past and future climates.
Matsumoto, K., and Jorge Sarmiento, 2008: A corollary to the silicic acid leakage hypothesis. Paleoceanography, 23(PA001515), doi:10.1029/2007PA001515
[ Abstract ]
The silicic acid leakage hypothesis (SALH) attempts to explain part of the large and regular atmospheric CO₂ changes over the last glacial-interglacial cycles. It calls for a reduction in the carbonate pump through a growth in diatoms at the expense of coccolithophorids in low-latitude surface waters, driven by a ��leakage�� of high-Si:N waters from the Southern Ocean. Recent studies that present low opal accumulation rates from the glacial eastern equatorial Pacific have challenged SALH. In a corollary to SALH, we argue that the key to SALH is the dominance of diatoms over coccolithophorids, and this does not depend on the magnitude of diatom production per se. In support of our claim, we show in a numerical model that atmospheric CO₂ can be lowered with even a reduced absolute flux of silicic acid leakage, provided that Si:N in the leakage is elevated and that the excess Si can be used by diatoms to shift the floral composition in their favor.
Mignone, B. K., Robert H. Socolow, Jorge Sarmiento, and Michael Oppenheimer, 2008: Atmospheric Stabilization and the Timing of Carbon Mitigation. Climatic Change, 88(3-4), doi:10.1007/S10584-007-9391-8 251-265
[ Abstract ]
Stabilization of atmospheric CO₂ concentrations below a pre-industrial doubling (~550 ppm) is a commonly cited target in climate policy assessment. When the rate at which future emissions can fall is assumed to be fixed, the peak atmospheric concentration � or the stabilization �frontier� � is an increasing and convex function of the length of postponement. Here we find that a decline in emissions of 1% year⁻¹ beginning today would place the frontier near 475 ppm and that when mitigation is postponed, options disappear (on average) at the rate of ~9 ppm year⁻¹, meaning that delays of more than a decade will likely preclude stabilization below a doubling. When constraints on the future decline rate of emissions are relaxed, a particular atmospheric target can be realized in many ways, with scenarios that allow longer postponement of emissions reductions requiring greater increases in the intensity of future mitigation. However, the marginal rate of substitution between future mitigation and present delay becomes prohibitively large when the balance is shifted too far toward the future, meaning that some amount of postponement cannot be fully offset by simply increasing the intensity of future mitigation. Consequently, these results suggest that a practical transition path to a given stabilization target in the most commonly cited range can allow, at most, one or two decades of delay.
Morel, Francois, A. B. Kustka, and Y. Shaked, 2008: The role of unchelated Fe in the iron nutrition of phytoplankton. Limnology and Oceanography, http://geoweb.princeton.edu/research/tracemetals/pdf/morel2008.pdf, 53(1), 400-404
[ Abstract ]
The important question of iron bioavailability in the sea has become complicated by the discovery that marine phytoplankton can take up Fe bound in very stable chelates via reductive processes, and some particular Fe species through specialized transport mechanisms. As a result there is some question of whether the small fraction of Fe that is ��free�� or unchelated in seawater is important in the nutrition of natural phytoplankton assemblages. A careful examination of published laboratory studies on Fe uptake by model organisms all support the idea that unchelated Fe (III) is highly available for uptake and that it is an important source of the Fe taken up by phytoplankton under a variety of experimental conditions. Comparing these results with field data on Fe speciation shows that unchelated Fe can be an important source of Fe to the phytoplankton in the sea: it is likely sufficient to contribute the bulk of the Fe supporting primary production in regions that are not limited by Fe and a significant fraction everywhere, including high-nutrient low-chlorophyll areas.
Oppenheimer, Michael, B. O'Neill, and M. Webster, 2008: Negative Learning. Climatic Change, 89(1-2), doi:10.1007/S10584-008-9405-1 155-172
[ Abstract ]
New technical information may lead to scientific beliefs that diverge over time from the a posteriori right answer. We call this phenomenon, which is particularly problematic in the global change arena, negative learning. Negative learning may have affected policy in important cases, including stratospheric ozone depletion, dynamics of the West Antarctic ice sheet, and population and energy projections. We simulate negative learning in the context of climate change with a formal model that embeds the concept within the Bayesian framework, illustrating that it may lead to errant decisions and large welfare losses to society. Based on these cases, we suggest approaches to scientific assessment and decision making that could mitigate the problem. Application of the tools of science history to the study of learning in global change, including critical examination of the assessment process to understand how judgments are made, could provide important insights on how to improve the flow of information to policy makers.
Perry, William, Alec Broers, Farouk El-Baz, and Robert H. Socolow, 2008: Grand Challenges for Engineering. National Academy of Sciences, http://www.engineeringchallenges.org/?ID=11574,
[ Abstract ]
A diverse committee of experts from around the world, some of the most accomplished engineers and scientists of their generation, proposed the 14 challenges outlined in this booklet. The panel, which was convened by the U.S. National Academy of Engineering (NAE) at the request of the U.S. National Science Foundation, did not rank the challenges selected, nor did it endorse particular approaches to meeting them. Rather than attempt to include every important goal for engineering, the panel chose opportunities that were both achievable and sustainable to help people and the planet thrive. The panel�s conclusions were reviewed by more than 50 subject-matter experts. In addition, the effort received worldwide input from prominent engineers and scientists, as well as from the general public. The NAE is offering an opportunity to comment on the challenges via the project�s interactive Web site at www.engineeringchallenges.org.
Purves, D. W., J W. Lichstein, N. Strigul, and Stephen W. Pacala, August 2008: Predicting and understanding forest dynamics using a simple tractable model. Proceedings of the National Academy of Sciences of the United States of America, www.pnas.org cgi doi 10.1073 pnas.0807754105, 105(44), 17018-17022,
[ Abstract ]
The perfect-plasticity approximation (PPA) is an analytically tractable model of forest dynamics, defined in terms of parameters for individual trees, including allometry, growth, and mortality. We estimated these parameters for the eight most common species on each of four soil types in the US Lake states (Michigan, Wisconsin, and Minnesota) by using short-term (<15-year) inventory data from individual trees. We implemented 100-year PPA simulations given these parameters and compared these predictions to chronosequences of stand development. Predictions for the timing and magnitude of basal area dynamics and ecological succession on each soil were accurate, and predictions for the diameter distribution of 100-year-old stands were correct in form and slope. For a given species, the PPA provides analytical metrics for early-successional performance (H₂₀, height of a 20-year-old open-grown tree) and late-successional performance (Z^*, equilibrium canopy height in monoculture). These metrics predicted which species were early or late successional on each soil type. Decomposing Z^*, showed that (i) succession is driven both by superior understory performance and superior canopy performance of late-successional species, and (ii) performance differences primarily reflect differences in mortality rather than growth. The predicted late-successional dominants matched chronosequences on xeromesic (Quercus rubra) and mesic (codominance by Acer rubrum and Acer saccharum) soil. On hydromesic and hydric soils, the literature reports that the current dominant species in old stands (Thuja occidentalis) is now failing to regenerate. Consistent with this, the PPA predicted that, on these soils, stands are now succeeding to dominance by other latesuccessional species (e.g., Fraxinus nigra, A. rubrum).
Purves, D. W., and Stephen W. Pacala, 2008: Predictive Models of Forest Dynamics. Science, Vol. 320(no. 5882), doi:10.1126/science.1155359 1452 - 1453
[ Abstract ]
Dynamic global vegetation models (DGVMs) have shown that forest dynamics could dramatically alter the response of the global climate system to increased atmospheric carbon dioxide over the next century. But there is little agreement between different DGVMs, making forest dynamics one of the greatest sources of uncertainty in predicting future climate. DGVM predictions could be strengthened by integrating the ecological realities of biodiversity and height-structured competition for light, facilitated by recent advances in the mathematics of forest modeling, ecological understanding of diverse forest communities, and the availability of forest inventory data.
Riebesell, U., R.G.J. Bellerby, A. Engel, V. J. Fabry, D. A. Hutchins, T. B. H. Reusch, K. G. Schulz, and Francois Morel, 2008: Comment on Phytoplankton Calcification in a High-CO₂ World. Science, 322, doi:10.1126/science.1161096 1466
[ Abstract ]
Iglesias-Rodriguez et al. (Research Articles, 18 April 2008, p. 336) reported that the coccolithophore Emiliania huxleyi doubles its organic matter production and calcification in response to high carbon dioxide partial pressures, contrary to previous laboratory and field studies. We argue that shortcomings in their experimental protocol compromise the interpretation of their data and the resulting conclusions.
Robinson, R. S., and Daniel Sigman, 2008: Nitrogen isotopic evidence for a poleward decrease in surface nitrate within the ice age Antarctic. Quaternary Science Reviews, 27(9-10), doi:10.1016/j.quascirev.2008.02.005 1076-1090
[ Abstract ]
Surface sediment diatom-bound δ¹⁵N along a latitudinal transect of 170�W shows a previously unobserved increase to the South of the Antarctic Polar Front. The southward δ¹⁵N increase is best explained by the combination of two changes toward the South, a decrease in the isotope effect of nitrate assimilation (ε) and an increase in the degree of nitrate consumption, both associated with shoaling of the mixed layer into the seasonal ice zone (SIZ). New downcore records show high amplitude changes in diatom-bound δ¹⁵N during the last ice age, with intervals of higher δ¹⁵N, including the last glacial maximum, the transition between marine isotope stages 5 and 4, and marine isotope stage 6, while other intervals are similar in δ¹⁵N to interglacial sediments. Variation in the range of 0�3%, as seen in previously published records, may be entirely due to changes in ε. However, the observed magnitude of the change of 4�10% in the three new records and the locations of these records relative to the modern meridional gradient in mixed layer depth appear to require increased nitrate consumption to explain the high-δ¹⁵N intervals. The new sites are near the modern Southern Antarctic Circumpolar Current Front (SACCF), and one of the sites has been shown to be associated with sporadic summer sea ice during the LGM. As with other Antarctic sites, the available proxy data suggest that they were characterized by lower export production. Based on these and other observations, we propose that the weak southward nitrate decrease in the modern Antarctic surface was a fully developed ��nutrient front�� in the glacial Antarctic, associated with the SACCF. Both modern ocean and paleoceanographic work is needed to test this hypothesis, which would have major implications for atmospheric CO₂.
Rodgers, K. B., Jorge Sarmiento, O. Aumont, C. Crevoisier, C.D.B. Mont�gut, and N. Metzl, 2008: A wintertime uptake window for anthropogenic CO₂ in the North Pacific. Global Biogeochemical Cycles, 22(GB2020), doi:10.1029/2006GB002920
[ Abstract ]
An ocean model has been forced with NCEP reanalysis fluxes over 1948�2003 to evaluate the pathways and timescales associated with the uptake of anthropogenic CO₂ over the North Pacific. The model reveals that there are two principal regions of uptake, the first in the region bounded by 35�45�N and 140�180�E, and the second along a band between 10�20�N and between 120�W and 180�E. For both of these regions, the dominant timescale of variability in uptake is seasonal, with maximum uptake occurring during winter and uptake being close to zero or slightly negative during summer when integrated over the basin. A decadal trend toward increased uptake of anthropogenic CO₂ consists largely of modulations of the uptake maximum in winter. For detection of anthropogenic changes, this implies that in situ measurements will need to resolve the seasonal cycle in order to capture decadal trends in ΔpCO₂. As uptake of anthropogenic CO₂ occurs preferentially during winter, observationally based estimates which do not resolve the full seasonal cycle may result in underestimates of the rate of uptake of anthropogenic CO₂. There is also a sizable circulation-driven decadal trend in the seasonal cycle of sea surface ΔpCO₂ for the North Pacific, with maximum changes found near the boundary separating the subtropical and subpolar gyres in western and central regions of the basin. These changes are due to a trend in the large-scale circulation of the gyres, which itself is driven by a trend in the wind stress over the basin scale. This trend in the three-dimensional circulation is more important than the local trend in mixed layer depth (MLD) in contributing to the decadal trend in ΔpCO₂.
Rodgers, K. B., O. Aumont, C. Menkes, and T. Gorgues, 2008: Decadal variations in equatorial Pacific ecosystems and ferrocline/pycnocline decoupling. Global Biogeochemical Cycles, 22(GB2019), doi:10.1029/2006GB002919
[ Abstract ]
The equatorial Pacific Ocean is known for its large interannual to decadal variability in circulation. In particular, the changes that occurred in 1976/1977 have received considerable attention in the climate dynamics literature, and recently there has been much attention focused on changes that may have occurred there in 1997/1998. Unfortunately, because of data sparsity, the impact of these changes or shifts on ocean biogeochemistry and ecosystems remains largely unknown. Here a three-dimensional ocean circulation model (the ORCA2 configuration of OPA) which has a food web/ biogeochemistry model (PISCES) embedded in it, and which has been forced with both NCEP-1 and ERA-40 reanalysis fluxes over multiple decades, is used as a tool to investigate decadal changes and their associated mechanisms. Our main finding with the model is that a decrease in the amplitude of the surface zonal wind stress in the tropical Pacific in the mid-to-late-1970s leads to a decrease in Fe and Chl concentrations in the upwelling regions of the eastern equatorial Pacific after 1976/ 1977. These changes find expression predominantly during the upwelling season (the seasonal maximum for Fe and Chl concentrations), when surface Fe and Chl concentrations tend to be significantly higher pre-1976/1977 than post-1976/1977. The changes in Chl concentrations need to be understood as modulations of the amplitude of the seasonal cycle, rather than as a ��biological regime shift�� (an abrupt transition from one mean state to another). In contrast to what is found for Fe and Chl, for NO₃ the decadal changes in surface concentrations in the upwelling region about 1976/1977 can be described as a shift in the mean state. It is shown that the response in surface Fe and Chl in the upwelling region about 1976/1977 is proportionally larger than the decadal changes in surface wind stress forcing, and it is also larger than the previously reported change in the strength of the meridional overturning strength of the subtropical cells (STCs). Importantly, this amplified response reflects a decoupling of the ferrocline and pycnocline within the equatorial Pacific. In this way, the presence of a time-invariant sediment source for Fe can substantially amplify the ecosystem response to decadal variability in ocean circulation.
Socolow, Robert H., 2008: Stabilization Wedges and Climate Change. Physics of Sustainable Energy: Using Energy Efficiently and Producing It Renewably. AIP Conf. Proc., 1044, doi:10.1063/1.2993727 28-48
[ Abstract ]
An informal pedagogical tour provides quantitative views of the magnitude of the challenge of mitigating climate change and many of the energy technologies available to address this challenge. The importance of energy efficiency is emphasized, as is the societal context for technological change.
Socolow, Robert H., 2008: The Critical Role of Energy Efficiency in Mitigating Global Warming. Government Law and Policy Journal, NY State Bar Association, Albany, NY, http://www.princeton.edu/mae/people/faculty/socolow/SocolownybarGLPJSum08.pdf, 10(1),
[ Abstract ]
This is the written version of a lecture presented to the Public Service Commission, State of New York, Proceeding on Motion of the Commission Regarding an Energy Efficiency Portfolio Standard. The lecture was given at the Albany Law School, Albany, New York, July 19, 2007.

This is reprinted with permission from the Government Law and Policy Journal.
Strigul, N., D. Pristinski, D. W. Purves, J. Dushoff, and Stephen W. Pacala, 2008: Scaling from Trees to Forests: Tractable Macroscopic Equations for Forest Dynamics. Ecological Monographs, 78(4), doi:10.1890/08-0082.1 523-525
[ Abstract ]
Individual-based forest simulators, such as TASS and SORTIE, are spatial stochastic processes that predict properties of populations and communities by simulating the fate of every plant throughout its life cycle. Although they are used for forest management and are able to predict dynamics of real forests, they are also analytically intractable, which limits their usefulness to basic scientists. We have developed a new spatial individual-based forest model that includes a perfect plasticity formulation for crown shape. Its structure allows us to derive an accurate approximation for the individual-based model that predicts mean densities and size structures using the same parameter values and functional forms, and also it is analytically tractable. The approximation is represented by a system of von Foerster partial differential equations coupled with an integral equation that we call the perfect plasticity approximation (PPA). We have derived a series of analytical results including equilibrium abundances for trees of different crown shapes, stability conditions, transient behaviors, such as the constant yield law and self-thinning exponents, and two species coexistence conditions.
Suwa, M., and Michael Bender, 2008: Chronology of the Vostok ice core constrained by O₂/N₂ ratios of occluded air, and its implication for the Vostok climate records. Quaternary Science Reviews, 27(11-12), doi:10.1016/j.quascirev.2008.02.017 1093-1106
[ Abstract ]
We present a timescale for the Vostok ice core that is derived by orbitally tuning to O₂/N₂ ratios in occluded air for depths deeper than 1550m (>112 ka), and by gas correlation to the GISP2 chronology for the section shallower than 1422m (<102 ka). Our chronology of the deeper section rests on the assumption that, during the bubble close off process, local summer insolation indirectly controls the extent of O₂ exclusion and hence the O₂/N₂ ratio in trapped gases. The newly derived O₂/N₂ chronology is consistent with absolutely dated speleothem records. The O₂/N₂ chronology differs from previously published orbital tuning chronologies (CH₄ and δ¹⁸O_atm) by up to ~ �6 kyr, and from the original GT4 chronology by up to ~15 kyr. The difference between the O₂/N₂ chronology and the δ¹⁸O_atm chronology varies in time with strong signals centered at 1/100 and 1/41 kyr^-1. The ages for the last four glacial terminations in Vostok correspond to high obliquity (>23.7� at terminations� midpoints). They also correspond with decreasing precession index, corresponding to increasing boreal summer insolation. The Vostok temperature record, boreal summer insolation, and the rate of change of the SPECMAP property (reflecting planktonic foram δ¹⁸O) with respect to time are highly coherent at precession and obliquity periods. These three properties vary almost synchronously, with the possibility that Vostok temperature lags behind the other two. Our new timescale supports the widespread view that boreal summer insolation played an important role in glacial�interglacial cycles.
Suwa, M., and Michael Bender, 2008: O₂/N₂ ratios of occluded air in the GISP2 ice core. Journal of Geophysical Research � Atmosphere, 113(D1119), doi:10.1029/2007JD009589
[ Abstract ]
We present and discuss the record of O₂/N₂ ratios in air occluded in the GISP2 ice core retrieved from Summit, Greenland. In this study, we examine results for 601 samples from 331 depths measured by 1994, and 92 samples from 46 depths newly measured in 2006. Poorly replicated samples, samples with no replicates and samples falling more than three standard deviations from the mean of each δO₂/N₂ data set are excluded from the analysis. The majority of poorly replicated samples are from the depth zone associated with the transition between gas in bubbles and gas present as clathrate hydrates. We found that the O₂/N₂ ratio of samples is depleted by an average value of 7.3% during 11 years of storage at -35°C O₂/N₂ ratios measured at various times were corrected for depletion during storage and combined to form a single data set. The stacked GISP2 δO₂/N₂ record shows strong spectral power at the orbital frequencies, and δO₂/N₂ is in antiphase with local summer insolation. This observation is consistent with the earlier findings for the Vostok and Dome Fuji ice cores from East Antarctica. It validates previous conclusions that fractionation during bubble close-off depends on ice grain properties set at the surface by solar insolation. In addition, the GISP2 δO₂/N₂ record shows millennial duration signals that are in phase with the local temperature record of rapid climate change. The exact mechanisms by which local summer insolation induces orbital variability in δO₂/N₂, and by which temperature (or related properties) induce high frequency signals in δO₂/N₂, remain to be identified.
Brunelle, B. G., Daniel Sigman, M. S. Cook, L. D. Keigwin, G. H. Haug, B. Plessen, G. Schettler, and S. L. Jaccard, 2007: Evidence from diatom-bound nitrogen isotopes for Subarctic Pacific stratification during the last ice age and a link to North Pacific denitrification changes. Paleoceanography, 22(PA1215), doi:10.1029/2005PA001205
[ Abstract ]
In a piston core from the central Bering Sea, diatom microfossil-bound N isotopes and the concentrations of opal, biogenic barium, calcium carbonate, and organic N are measured over the last glacial/interglacial cycle. Compared to the interglacial sections of the core, the sediments of the last ice age are characterized by 3% higher diatom-bound δ¹⁵N, 70 wt % lower opal content and 1200 ppm lower biogenic barium. Taken together and with constraints on sediment accumulation rate, these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the Bering Sea during glacial times, with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition. This finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification. In addition, we hypothesize that more complete nutrient consumption in the glacial age subarctic Pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical North Pacific by lowering the nutrient content of the intermediate-depth water formed in the subpolar North Pacific. In the deglacial interval of the Bering Sea record, two apparent peaks in export productivity are associated with maxima in diatom-bound and bulk sediment δ¹⁵N. The high δ¹⁵N in these intervals may have resulted from greater surface nutrient consumption during this period. However, the synchroneity of the deglacial peaks in the Bering Sea with similar bulk sediment δ¹⁵N changes in the eastern Pacific margin and the presence of sediment lamination within the Bering Sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the δ¹⁵N of the nitrate feeding Bering Sea surface waters at these times.
Chu, S., J. Goldenberg, S. Arungu Olende, M. El-Ashry, G. Davis, T. B. Johansson, D. W. Keith, J. Li, N. Nakicenovic, R. Pachauri, M. Shafie-Pour, E. Shpilrain, Robert H. Socolow, K. Yamaji, and L. Yan, October 2007: Lighting the way - Toward a sustainable energy future. A Report to the InterAcademy Council, http://royalsociety.org/downloaddoc.asp?id=4695,
[ Abstract ]
Making the transition to a sustainable energy future is one of the central challenges humankind faces in this century. The concept of energy sustainability encompasses not only the imperative of securing adequate energy to meet future needs, but doing so in a way that (a) is compatible with preserving the underlying integrity of essential natural systems, including averting dangerous climate change; (b) extends basic energy services to the more than 2 billion people worldwide who currently lack access to modern forms of energy; and (c) reduces the security risks and potential for geopolitical conflict that could otherwise arise from an escalating competition for unevenly distributed energy resources.
Crevoisier, C., E. Shevliakova, M. N. Gloor, C. Wirth, and Stephen W. Pacala, 2007: Drivers of fires in the boreal forests: data constrained design of a prognostic model for burned area for use in dynamic global vegetation models. Journal of Geophysical Research, 112(D24112), doi:10.1029/2006JD008372
[ Abstract ]
Boreal regions are an important component of the global carbon cycle because they host large stocks of aboveground and belowground carbon. Since boreal forest evolution is closely related to fire regimes, shifts in climate are likely to induce changes in ecosystems, potentially leading to a large release of carbon and other trace gases to the atmosphere. Prediction of the effect of this potential climate feedback on the Earth system is therefore important and requires the modeling of fire as a climate driven process in dynamic global vegetation models (DGVMs). Here, we develop a new data-based prognostic model, for use in DGVMs, to estimate monthly burned area from four climate (precipitation, temperature, soil water content and relative humidity) and one humanrelated (road density) predictors for boreal forest. The burned area model is a function of current climatic conditions and is thus responsive to climate change. Model parameters are estimated using a Markov Chain Monte Carlo method applied to on ground observations from the Canadian Large Fire Database. The model is validated against independent observations from three boreal regions: Canada, Alaska and Siberia. Provided realistic climate predictors, the model is able to reproduce the seasonality, intensity and interannual variability of burned area, as well as the location of fire events. In particular, the model simulates well the timing of burning events, with two thirds of the events predicted for the correct month and almost all the rest being predicted 1 month before or after the observed event. The predicted annual burned area is in the range of various current estimates. The estimated annual relative error (standard deviation) is twelve percent in a grid cell, which makes the model suitable to study quantitatively the evolution of burned area with climate.
de Boer, A. M., Daniel Sigman, J. R. Toggweiler, and J. L. Russell, 2007: The Effect of global ocean temperature change on deep ocean ventilation. Paleoceanography, 22(PA2210), doi:10.1029/2005PA001242
[ Abstract ]
A growing number of paleoceanographic observations suggest that the ocean�s deep ventilation is stronger in warm climates than in cold climates. Here we use a general ocean circulation model to test the hypothesis that this relation is due to the reduced sensitivity of seawater density to temperature at low mean temperature; that is, at lower temperatures the surface cooling is not as effective at densifying fresh polar waters and initiating convection. In order to isolate this factor from other climate-related feedbacks we change the model ocean temperature only where it is used to calculate the density (to which we refer below as ��dynamic�� temperature change). We find that a dynamically cold ocean is globally less ventilated than a dynamically warm ocean. With dynamic cooling, convection decreases markedly in regions that have strong haloclines (i.e., the Southern Ocean and the North Pacific), while overturning increases in the North Atlantic, where the positive salinity buoyancy is smallest among the polar regions. We propose that this opposite behavior of the North Atlantic to the Southern Ocean and North Pacific is the result of an energy-constrained overturning.
Deutsch, C., Jorge Sarmiento, Daniel Sigman, N. Gruber, and J. P. Dunne, 2007: Spatial coupling of nitrogen inputs and losses in the ocean. Nature, 445, doi:10.1038/nature05392
[ Abstract ]
Nitrogen fixation is crucial for maintaining biological productivity in the oceans, because it replaces the biologically available nitrogen that is lost through denitrification. But, owing to its temporal and spatial variability, the global distribution of marine nitrogen fixation is difficult to determine from direct shipboard measurements. This uncertainty limits our understanding of the factors that influence nitrogen fixation, which may include iron, nitrogen-to-phosphorus ratios, and physical conditions such as temperature. Here we determine nitrogen fixation rates in the world�s oceans through their impact on nitrate and phosphate concentrations in surface waters, using an ocean circulation model. Our results indicate that nitrogen fixation rates are highest in the Pacific Ocean, where water column denitrification rates are high but the rate of atmospheric iron deposition is low. We conclude that oceanic nitrogen fixation is closely tied to the generation of nitrogen-deficient waters in denitrification zones, supporting the view that nitrogen fixation stabilizes the oceanic inventory of fixed nitrogen over time.
Donner, S. D., T. R. Knutson, and Michael Oppenheimer, 2007: Model-based assessment of the role of human-induced climate change in the 2005 Caribbean coral bleaching event. Proceedings of the National Academy of Sciences of the United States of America, 104(13), doi:10.1073/pnas.0610122104 5483-5488
[ Abstract ]
Episodes of mass coral bleaching around the world in recent decades have been attributed to periods of anomalously warm ocean temperatures. In 2005, the sea surface temperature (SST) anomaly in the tropical North Atlantic that may have contributed to the strong hurricane season caused widespread coral bleaching in the Eastern Caribbean. Here, we use two global climate models to evaluate the contribution of natural climate variability and anthropogenic forcing to the thermal stress that caused the 2005 coral bleaching event. Historical temperature data and simulations for the 1870�2000 period show that the observed warming in the region is unlikely to be due to unforced climate variability alone. Simulation of background climate variability suggests that anthropogenic warming may have increased the probability of occurrence of significant thermal stress events for corals in this region by an order of magnitude. Under scenarios of future greenhouse gas emissions, mass coral bleaching in the Eastern Caribbean may become a biannual event in 20�30 years. However, if corals and their symbionts can adapt by 1� 1.5�C, such mass bleaching events may not begin to recur at potentially harmful intervals until the latter half of the century. The delay could enable more time to alter the path of greenhouse gas emissions, although long-term ��committed warming�� even after stabilization of atmospheric CO₂ levels may still represent an additional long-term threat to corals.
Dunne, J. P., Jorge Sarmiento, and A. Gnanadesikan, 2007: A synthesis of global particle export from the surface ocean and cycling through the ocean interior and on the seafloor. Global Biogeochemical Cycles, 21(GB4006), doi:10.1029/2006GB002907
[ Abstract ]
We present a new synthesis of the oceanic cycles of organic carbon, silicon, and calcium carbonate. Our calculations are based on a series of algorithms starting with satellite-based primary production and continuing with conversion of primary production to sinking particle flux, penetration of particle flux to the deep sea, and accumulation in sediments. Regional and global budgets from this synthesis highlight the potential importance of shelves and near-shelf regions for carbon burial. While a high degree of uncertainty remains, this analysis suggests that shelves, less than 50 m water depths accounting for 2% of the total ocean area, may account for 48% of the global flux of organic carbon to the seafloor. Our estimates of organic carbon and nitrogen flux are in generally good agreement with previous work while our estimates for CaCO₃ and SiO₂ fluxes are lower than recent work. Interannual variability in particle export fluxes is found to be relatively small compared to intra-annual variability over large domains with the single exception of the dominating role of El Nin�o-Southern Oscillation variability in the central tropical Pacific. Comparison with available sediment-based syntheses of benthic remineralization and burial support the recent theory of mineral protection of organic carbon flux through the deep ocean, pointing to lithogenic material as an important carrier phase of organic carbon to the deep seafloor. This work suggests that models which exclude the role of lithogenic material would underestimate the penetration of POC to the deep seafloor by approximately 16�51% globally, and by a much larger fraction in areas with low productivity. Interestingly, atmospheric dust can only account for 31% of the total lithogenic flux and 42% of the lithogenically associated POC flux, implying that a majority of this material is riverine or directly erosional in origin.
Galbraith, E. D., S. L. Jaccard, T. F. Pedersen, Daniel Sigman, G. H. Haug, M. S. Cook, J. R. Southon, and R. Francois, 2007: Carbon dioxide release from the North Pacific abyss during the last deglaciation. Nature, doi:10.1038/nature06227 890-893
[ Abstract ]
Atmospheric carbon dioxide concentrations were significantly lower during glacial periods than during intervening interglacial periods, but the mechanisms responsible for this difference remain uncertain. Many recent explanations call on greater carbon storage in a poorly ventilated deep ocean during glacial periods, but direct evidence regarding the ventilation and respired carbon content of the glacial deep ocean is sparse and often equivocal. Here we present sedimentary geochemical records from sites spanning the deep subarctic Pacific that - together with previously published results - show that a poorly ventilated water mass containing a high concentration of respired carbon dioxide occupied the North Pacific abyss during the Last Glacial Maximum. Despite an inferred increase in deep Southern Ocean ventilation during the first step of the deglaciation (18,000�15,000 years ago), we find no evidence for improved ventilation in the abyssal subarctic Pacific until a rapid transition 14,600 years ago: this change was accompanied by an acceleration of export production from the surface waters above but only a small increase in atmospheric carbon dioxide concentration. We speculate that these changes were mechanistically linked to a roughly coeval increase in deep water formation in the North Atlantic, which flushed respired carbon dioxide from northern abyssal waters, but also increased the supply of nutrients to the upper ocean, leading to greater carbon dioxide sequestration at mid-depths and stalling the rise of atmospheric carbon dioxide concentrations. Our findings are qualitatively consistent with hypotheses invoking a deglacial flushing of respired carbon dioxide from an isolated, deep ocean reservoir, but suggest that the reservoir may have been released in stages, as vigorous deep water ventilation switched between North Atlantic and Southern Ocean source regions.
Gloor, M. N., E. Dlugokensky, C. Brenninkmeijer, L. W. Horowitz, D. F. Hurst, G. Dutton, C. Crevoisier, T. Machida, and P. P. Tans, 2007: Three-dimensional SF₆ data and tropospheric transport simulations: Signals, modeling accuracy, and implications for inverse modeling. Journal of Geophysical Research, 112(D15112), doi:10.1029/2006JD007973
[ Abstract ]
Surface emissions of SF₆ are closely tied to human activity and thus fairly well known. They therefore can and have been used to evaluate tropospheric transport predicted by models. A range of new atmospheric SF₆ data permit us to expand on earlier studies. The purpose of this first of two papers is to characterize known and new transport constraints provided by the data and to use them to quantify predictive skill of the MOZART-2 atmospheric chemistry and transport model. Main noteworthy observational constraints are (1) a well-known steep N-S gradient at the surface confined to an ≈40� wide latitude band in the tropics; (2) a fairly uniform N-S gradient in the upper troposphere; (3) an increase in the temporal variation in upper troposphere Northern Hemisphere records with increasing latitude; (4) a negative SF₆ gradient in Northern Hemisphere vertical profiles from the surface to 8 km height, but a positive gradient in the Southern Hemisphere; and (5) a clear reflection in surface records of large-scale seasonal atmosphere movements like the undulations of the Intertropical Convergence Zone (ITCZ). Comparison of observations with simulations reveal excellent modeling skills with regards to (1) large-scale annual mean latitudinal gradients at remote surface sites (relative bias of N-S hemisphere difference ≤ 5%) and aloft (≈10 km, relative bias ≤ 25%); (2) seasonality in signals at remote sites caused by large-scale movements of the atmosphere; (3) time variation in upper troposphere records; (4) ��faithfulness�� of advective transport on timescales up to ≈1 week; and (5) the general shapes and seasonal variation of vertical profiles. The model (1) underestimates the variation in the vertical of profiles, particularly those from locations close to high emissions regions, and (2) overestimates the difference in SF₆ between the planetary boundary layer (PBL) and free troposphere over North America, and thus likely Eurasia, during winter by approximately a factor of 2 (STD ≈ 100%). The comparisons permit estimating lower bounds on representation errors which are large for sites close to continental outflow regions. Given the magnitude of the signals and signal variance, SF₆ provides a strong constraint on interhemispheric transport, PBL ventilation, dispersion pathways of northern midlatitude surface emissions through the upper troposphere, and large-scale movements of the atmosphere.
Gorgues, T., C. Menkes, O. Aumont, Y. Dandonneau, G. Madec, and K. B. Rodgers, 2007: Indonesian Throughflow control of the eastern equatorial Pacific biogeochemistry. Geophysical Research Letters, 34(L05609), doi:10.1029/2006GL028210
[ Abstract ]
Two model simulations were performed to address the influence of the Indonesian throughflow (ITF) on the biogeochemical state of the equatorial Pacific. A simulation where the ITF is open is compared with an experiment where it is closed, and it is first shown that the impacts on the physical circulation are consistent with what has been found in previous modelling studies. In terms of biochemistry, closing the ITF results in increased iron concentration at the origin of the Equatorial Undercurrent (EUC). But the 11Sv of water otherwise transferred to the Indian Ocean remain in the equatorial Pacific, which result in a 30 m deepening of the thermocline/ferricline in the eastern Pacific. This deepening decreases the iron concentration of the equatorial wind driven upwelled water and cancels the iron increase advected by the EUC. The iron decrease of the equatorial upwelled water leads to decrease primary production by 15% along the equator.
Greenblatt, J. B., Samir Succar, D. C. Denkenberger, Robert H. Williams, and Robert H. Socolow, 2007: Baseload wind energy: Modeling the competition between gas turbines and compressed air energy storage for supplemental generation. Energy Policy, 35(3), doi:10.1016/j.enpol.2006.03.023 1474-1492
[ Abstract ]
The economic viability of producing baseload wind energy was explored using a cost-optimization model to simulate two competing systems: wind energy supplemented by simple- and combined cycle natural gas turbines (��wind+gas��), and wind energy supplemented by compressed air energy storage (��wind+CAES��). Pure combined cycle natural gas turbines (��gas��) were used as a proxy for conventional baseload generation. Long-distance electric transmission was integral to the analysis. Given the future uncertainty in both natural gas price and greenhouse gas (GHG) emissions price, we introduced an effective fuel price, p_NGeff, being the sum of the real natural gas price and the GHG price. Under the assumption of p_NGeff = $5/GJ (lower heating value), 650W/m² wind resource, 750km transmission line, and a fixed 90% capacity factor, wind+CAES was the most expensive system at ¢6.0/kWh, and did not break even with the next most expensive wind+gas system until p_NGeff = $9.0/GJ. However, under real market conditions, the system with the least dispatch cost (short-run marginal cost) is dispatched first, attaining the highest capacity factor and diminishing the capacity factors of competitors, raising their total cost. We estimate that the wind+CAES system, with a greenhouse gas (GHG) emission rate that is onefourth of that for natural gas combined cycle plants and about one-tenth of that for pulverized coal plants, has the lowest dispatch cost of the alternatives considered (lower even than for coal power plants) above a GHG emissions price of $35/tC_equiv., with good prospects for realizing a higher capacity factor and a lower total cost of energy than all the competing technologies over a wide range of effective fuel costs. This ability to compete in economic dispatch greatly boosts the market penetration potential of wind energy and suggests a substantial growth opportunity for natural gas in providing baseload power via wind+CAES, even at high natural gas prices.
Houlton, B. Z., Daniel Sigman, E.A.G. Schuur, and L.O. Hedin, 2007: A climate-driven switch in plant nitrogen acquisition within tropical forest communities. Proceedings of the National Academy of Sciences of the United States of America, 104(21), doi:10.1073/pnas.0609935104 8902-8906
[ Abstract ]
The response of tropical forests to climate change will depend on individual plant species� nutritional strategies, which have not been defined in the case of the nitrogen nutrition that is critical to sustaining plant growth and photosynthesis. We used isotope natural abundances to show that a group of tropical plant species with diverse growth strategies (trees and ferns, canopy, and subcanopy) relied on a common pool of inorganic nitrogen, rather than specializing on different nitrogen pools. Moreover, the tropical species we examined changed their dominant nitrogen source abruptly, and in unison, in response to precipitation change. This threshold response indicates a coherent strategy among species to exploit the most available form of nitrogen in soils. The apparent community-wide flexibility in nitrogen uptake suggests that diverse species within tropical forests can physiologically track changes in nitrogen cycling caused by climate change.
Iudicone, D., K. B. Rodgers, R. Schopp, and G. Madec, 2007: An Exchange window for the injection of Antarctic Intermediate Water into the South Pacific. Journal of Physical Oceanography, 37, doi:10.1175/JPO2985.1 31-49
[ Abstract ]
Antarctic Intermediate Water (AAIW) occupies the intermediate horizon of most of the world oceans. Formed in the Southern Ocean, it is characterized by a relative salinity minimum. With a new, denser in situ National Oceanographic Data Center dataset, the authors have reanalyzed the export characteristics of AAIW from the Southern Ocean into the South Pacific Ocean. These new data show that part of the AAIW is exported from the subpolar frontal region by the large-scale circulation through an exchange window of 10� width situated east of 90�W in the southeast corner of the Pacific basin. This suggests the origin of this water to be in the Antarctic Circumpolar Current. A set of numerical modeling experiments has been used to reproduce these observed features and to demonstrate that the dynamics of the exchange window is controlled by the basin-scale meridional pressure gradient. The exchange of AAIW between the Southern and Pacific Oceans must therefore be understood in the context of the large basin-scale dynamical balance rather than simply local effects.
Jacobson, A. R., S. E. Mikaloff-Fletcher, N. Gruber, Jorge Sarmiento, and M. N. Gloor, 2007: A joint atmosphere-ocean inversion for surface fluxes of carbon dioxide: I. Methods and global-scale fluxes. Global Biogeochemical Cycles, 21(GB1019), doi:10.1029/2005GB002556
[ Abstract ]
We have constructed an inverse estimate of surface fluxes of carbon dioxide using both atmospheric and oceanic observational constraints. This global estimate is spatially resolved into 11 land regions and 11 ocean regions, and is calculated as a temporal mean for the period 1992�1996. The method interprets in situ observations of carbon dioxide concentration in the ocean and atmosphere with transport estimates from global circulation models. Uncertainty in the modeled circulation is explicitly considered in this inversion by using a suite of 16 atmospheric and 10 oceanic transport simulations. The inversion analysis, coupled with estimates of river carbon delivery, indicates that the open ocean had a net carbon uptake from the atmosphere during the period 1992�96 of 1.7 PgC yr^-1, consisting of an uptake of 2.1 PgC yr^-1 of anthropogenic carbon and a natural outgassing of about 0.5 PgC yr^-1 of carbon fixed on land and transported through rivers to the open ocean. The formal uncertainty on this oceanic uptake, despite a comprehensive effort to quantify sources of error due to modeling biases, uncertain riverine carbon load, and biogeochemical assumptions, is driven down to 0.2 PgC yr^-1 by the large number and relatively even spatial distribution of oceanic observations used. Other sources of error, for which quantifiable estimates are not currently available, such as unresolved transport and large region inversion bias, may increase this uncertainty.
Jacobson, A. R., S. E. Mikaloff-Fletcher, N. Gruber, Jorge Sarmiento, and M. N. Gloor, 2007: A joint atmosphere-ocean inversion for surface fluxes of carbon dioxide: II. Regional results. Global Biogeochemical Cycles, 21(GB1020), doi:10.1029/2006GB002703
[ Abstract ]
We report here the results from a coupled ocean-atmosphere inversion, in which atmospheric CO₂ gradients and transport simulations are combined with observations of ocean interior carbon concentrations and ocean transport simulations to provide a jointly constrained estimate of air-sea and air-land carbon fluxes. While atmospheric data have little impact on regional air-sea flux estimates, the inclusion of ocean data drives a substantial change in terrestrial flux estimates. Our results indicate that the tropical and southern land regions together are a large source of carbon, with a 77% probability that their aggregate source size exceeds 1 PgC yr^-1. This value is of similar magnitude to estimates of fluxes in the tropics due to land-use change alone, making the existence of a large tropical CO₂ fertilization sink unlikely. This terrestrial result is strongly driven by oceanic inversion results that differ from flux estimates based on ΔpCO₂ climatologies, including a relatively small Southern Ocean sink (south of 44°S) and a relatively large sink in the southern temperate latitudes (44°S�18°S). These conclusions are based on a formal error analysis of the results, which includes uncertainties due to observational error transport and other modeling errors, and biogeochemical assumptions. A suite of sensitivity tests shows that these results are generally robust, but they remain subject to potential sources of unquantified error stemming from the use of large inversion regions and transport biases common to the suite of available transport models.
Keller, Klaus, S.-R. Kim, J. Baehr, David F. Bradford, and Michael Oppenheimer, 2007: What is the economic value of information about climate thresholds? Human-Induced Climate Change: An Interdisciplinary Assessment, Cambridge University Press, Cambridge, MA, http://www.geosc.psu.edu/~kkeller/Keller_snowmass_pp_07.pdf, (Chapter 28), 343-354
[ Abstract ]
The field of integrated assessment of climate change is undergoing a paradigm shift towards the analysis of potentially abrupt and irreversible climate changes (Alley et al., 2003; Keller et al., 2006b). Early integrated studies broke important new ground in exploring the relationship between the costs and benefits of reducing carbon dioxide (CO₂) emissions (e.g., Nordhaus, 1991; Manne and Richels, 1991; or Tol, 1997). These studies project the climate response to anthropogenic CO₂ emissions to be relatively smooth and trypically conclude that the projected benefits of reducing CO₂ emissions would justify only small reductions in CO₂ emissions in a cost-benefit framework. The validity of the often-assumed smooth climate response is, however, questionable, given how that climate system has responded to forcing in the geological past. Before the Anthropocene, the geological time period where humans have started to influence the global biogeochemical cycles considerably (Crutzen, 2002) , the predominant responses of the climate system were forced by small changes in solar insolation occurring on timescales of thousands of years (Berger and Loutre, 1991). Yet this slow and smooth forcing apparently triggered abrupt climate changes - a threshold response where the climate system moved between different basins of attraction (Berger, 1990; Clement et al., 2001). Anthropogenic forcing may trigger climate threshold responses in the future (Alley et al., 2003; Keller et al., 2006b). Examples of such threshold responses include (i) a collapse of the North Atlantic meridional overturning circulation (Rahmstorf, 2000; Stommel, 1961), (ii) a disintegration of the West Antarctic Ice Sheet (Mercer, 1978; Oppenheimer, 1998), (iii) abrupt vegetation changes (Claussen et al., 1999; Scheffer et al., 2001), or (iv) changes in properties of the El Nino Southern Oscillation, ENSO (Fedorov and Philander, 2000; Timmermann, 201). Here we focus on the first two examples: a possible collapse of the North Atlantic meridional overturning circulation and a possible disintegration of the West Antarctic Ice Sheet. Our analysis address three main questions. (i) What underlying mechanisms define a climate threshold? (ii) What are the key scientific uncertainties in predicting whether these thresholds may be crossed in the future? (iii) What might be reasonable order-of-magnitude estimates of the expected economic value of reducing these uncertainties? Our analysis suggests that climate strategies designed to reduce the risk of crossing climate thresholds have to be designed in the face of large uncertainties. Some of the key uncertainties (e.g., the sensitivity of the meridional overturning circulation to anthropogenic greenhouse gas emissions) can be reduced by observation systems. We conclude by identifying future research needs.
Keller, Klaus, A. Robinson, David F. Bradford, and Michael Oppenheimer, 2007: The regrets of procrastination in climate policy. Environmental Research Letters, (Lett 2, No. 2), doi:10.1088/1748-9326/2/2/024004
[ Abstract ]
Anthropogenic carbon dioxide (CO₂) emissions are projected to impose economic costs due to the associated climate change impacts. Climate change impacts can be reduced by abating CO₂ emissions. What would be an economically optimal investment in abating CO₂ emissions? Economic models typically suggest that reducing CO₂ emissions by roughly ten to twenty per cent relative to business-as-usual would be an economically optimal strategy. The currently implemented CO₂ abatement of a few per cent falls short of this benchmark. Hence, the global community may be procrastinating in implementing an economically optimal strategy. Here we use a simple economic model to estimate the regrets of this procrastination�the economic costs due to the suboptimal strategy choice. The regrets of procrastination can range from billions to trillions of US dollars. The regrets increase with increasing procrastination period and with decreasing limits on global mean temperature increase. Extended procrastination may close the window of opportunity to avoid crossing temperature limits interpreted by some as �dangerous anthropogenic interference with the climate system� in the sense of Article 2 of the United Nations Framework Convention on Global Climate Change.
Lichstein, J W., J. Dushoff, S. A. Levin, and Stephen W. Pacala, 2007: Intraspecific variation and species coexistence. American Naturalist, 170(6), doi:10.1086/522937 807-818
[ Abstract ]
We use a two-species model of plant competition to explore the effect of intraspecific variation on community dynamics. The competitive ability (�performance�) of each individual is assigned by an independent random draw from a species-specific probability distribution. If the density of individuals competing for open space is high (e.g., because fecundity is high), species with high maximum (or large variance in) performance are favored, while if density is low, species with high typical (e.g., mean) performance are favored. If there is an interspecific mean-variance performance trade-off, stable coexistence can occur across a limited range of intermediate densities, but the stabilizing effect of this trade-off appears to be weak. In the absence of this trade-off, one species is superior. In this case, intraspecific variation can blur interspecific differences (i.e., shift the dynamics toward what would be expected in the neutral case), but the strength of this effect diminishes as competitor density increases. If density is sufficiently high, the inferior species is driven to extinction just as rapidly as in the case where there is no overlap in performance between species. Intraspecific variation can facilitate coexistence, but this may be relatively unimportant in maintaining diversity in most real communities.
Meckler, A. N., G. H. Haug, Daniel Sigman, B. Plessen, L. C. Peterson, and H. R. Thierstein, 2007: Detailed sedimentary N isotope records from Cariaco Basin for Terminations I and V: Local and global implications. Global Biogeochemical Cycles, 21(GB4019), doi:10.1029/2006GB002893
[ Abstract ]
For the last deglaciation and Termination V (the initiation of MIS 11 at around 430 ka) we report high-resolution sedimentary nitrogen isotope (δ¹⁵N) records from Cariaco Basin in the Caribbean Sea. During both terminations the previously reported interglacial decrease in δ¹⁵N clearly lags local changes such as water column anoxia as well as global increases in denitrification by several thousand years. On top of the glacialinterglacial change, several δ¹⁵N peaks were observed during the last deglaciation. The deglacial signal in Cariaco Basin can be best explained as a combination of (1) local variations in suboxia and water column denitrification as the reason for the millennialscale peaks, (2) a deglacial maximum in mean ocean nitrate δ¹⁵N, and (3) increasing N₂ fixation in response to globally increased denitrification causing the overall deglacial δ¹⁵N decrease. In the Holocene, much of the decrease in δ¹⁵N occurred between 6 and 3 ka, coinciding with an expected precession-modulated increase in African dust transport to the tropical North Atlantic and the Caribbean. This begs the hypothesis that N₂ fixation in this region increased in response to interglacial maxima in denitrification elsewhere but that this response strengthened with increased mid-Holocene iron input. It remains to be seen whether the data for MIS 11 support this interpretation.
Mikaloff-Fletcher, S. E., N. Gruber, A. R. Jacobson, M. N. Gloor, S. C. Doney, S. Dutkiewicz, M. Gerber, M. Follows, F. Joos, K. Lindsay, D. Menemenlis, and A. Mouchet, et al., 2007: Inverse estimates of the oceanic sources and sinks of natural CO₂ and the implied oceanic carbon transport. Global Biogeochemical Cycles, 21(GB1010), doi:10.1029/2006GB002751
[ Abstract ]
We use an inverse method to estimate the global-scale pattern of the air-sea flux of natural CO₂, i.e., the component of the CO₂ flux due to the natural carbon cycle that already existed in preindustrial times, on the basis of ocean interior observations of dissolved inorganic carbon (DIC) and other tracers, from which we estimate ΔC_gasex, i.e., the component of the observed (DIC that is due to the gas exchange of natural CO₂. We employ a suite of 10 different Ocean General Circulation Models (OGCMs) to quantify the error arising from uncertainties in the modeled transport required to link the interior ocean observations to the surface fluxes. The results from the contributing OGCMs are weighted using a model skill score based on a comparison of each model�s simulated natural radiocarbon with observations. We find a pattern of air-sea flux of natural CO₂ characterized by outgassing in the Southern Ocean between 44�S and 59�S, vigorous uptake at midlatitudes of both hemispheres, and strong outgassing in the tropics. In the Northern Hemisphere and the tropics, the inverse estimates generally agree closely with the natural CO₂ flux results from forward simulations of coupled OGCM-biogeochemistry models undertaken as part of the second phase of the Ocean Carbon Model Intercomparison Project (OCMIP-2). The OCMIP-2 simulations find far less air-sea exchange than the inversion south of 20�S, but more recent forward OGCM studies are in better agreement with the inverse estimates in the Southern Hemisphere. The strong source and sink pattern south of 20�S was not apparent in an earlier inversion study, because the choice of region boundaries led to a partial cancellation of the sources and sinks. We show that the inversely estimated flux pattern is clearly traceable to gradients in the observed ΔC_gasex, and that it is relatively insensitive to the choice of OGCM or potential biases in ΔC_gasex. Our inverse estimates imply a southward interhemispheric transport of 0.31 � 0.02 Pg C yr^-1, most of which occurs in the Atlantic. This is considerably smaller than the 1 Pg C yr^-1 of Northern Hemisphere uptake that has been inferred from atmospheric CO₂ observations during the 1980s and 1990s, which supports the hypothesis of a Northern Hemisphere terrestrial sink.
Naik, V., D. L. Mauzerall, L. W. Horowitz, M. D. Schwarzkopf, V. Ramaswamy, and Michael Oppenheimer, 2007: On the sensitivity of radiative forcing from biomass burning aerosols and ozone to emission location. Geophysical Research Letters, 34(L03818), doi:10.1029/2006GL028149
[ Abstract ]
Biomass burning is a major source of air pollutants, some of which are also climate forcing agents. We investigate the sensitivity of direct radiative forcing due to tropospheric ozone and aerosols (carbonaceous and sulfate) to a marginal reduction in their (or their precursor) emissions from major biomass burning regions. We find that the largest negative global forcing is for 10% emission reductions in tropical regions, including Africa (-4.1 mWm-2 from gas and -4.1 mWm-2 from aerosols), and South America (-3.0 mWmfrom gas and -2.8 mWmfrom aerosols). We estimate that a unit reduction in the amount of biomass burned in India produces the largest negative ozone and aerosol forcing. Our analysis indicates that reducing biomass burning emissions causes negative global radiative forcing due to ozone and aerosols; however, regional differences need to be considered when evaluating controls on biomass burning to mitigate global climate change.
Najjar, R. G., X. Jin, F. Louanchi, O. Aumont, K. Caldeira, S. C. Doney, J. C. Dutay, M. Follows, N. Gruber, F. Joos, K. Lindsay, and E. Maier-Reimer, et al., 2007: Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocean: Results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2). Global Biogeochemical Cycles, 21(GB3007), doi:10.1029/2006GB002857
[ Abstract ]
Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (�1σ) downward flux of organic matter across 75 m depth is 17 � 6 Pg C yr^-1. Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.
N�vdal, E., and Michael Oppenheimer, 2007: The Economics of the Thermohaline Circulation � A Problem with Multiple Thresholds of Unknown Locations. Resource and Energy Economics, 27(4), doi:10.1016/j.reseneeco.2007.01.003 262-283
[ Abstract ]
A potentially serious environmental threat facing humanity is the possibility of a collapse of the thermohaline circulation. Resulting climate changes, including absolute cooling near Greenland and northwest Europe, could be abrupt. Collapse of the thermohaline circulation may be triggered if the temperature or the rate of temperature change exceeds certain thresholds. The locations of these thresholds are unknown. Economic regulation of this problem requires solution methods for a class of dynamic optimization problems with multiple thresholds located in n-dimensional space. This class of problems has hitherto not been discussed in the literature. We present a model for the economic regulation of CO₂ emissions in the presence of threshold-triggered risk of a collapsing thermohaline circulation and derive optimality conditions for regulation.
Oppenheimer, Michael, B. O'Neill, M. Webster, and S. Agrawala, 2007: Climate Change: The Limits of Consensus. Science, 317, doi:10.1126/science.1144831 1505-1506
[ Abstract ]
The Intergovernmental Panel on Climate Change (IPCC) has just delivered its Fourth Assessment Report (AR4) since 1990. The IPCC was a bold innovation when it was established, and its accomplishments are singular (1, 2). It was the conclusion in the IPCC First Assessment Report that the world is likely to see �a rate of increase of global mean temperature during the next century � that is greater than seen over the past 10,000 years� (3) that proved influential in catalyzing the negotiation of the United Nations Framework Convention on Climate Change. The conclusions of the Second Assessment with regard to the human influence on climate (4) marked a paradigm shift in the policy debate that contributed to the negotiation of the Kyoto Protocol. IPCC conclusions from the Third, and now the Fourth, assessments have further solidified consensus behind the role of humans in changing the earth�s climate.
Pacala, Stephen W., et al., 2007: The North American Carbon Budget Past and Present. The First State of the Carbon Cycle Report (SOCCR), http://www.treesearch.fs.fed.us/pubs/13120,
[ Abstract ]
North America is currently a net source of carbon dioxide to the atmosphere, contributing to the global buildup of greenhouse gases in the atmosphere and associated changes in the Earth�s climate. In 2003, North America emitted nearly two billion metric tons of carbon to the atmosphere as carbon dioxide. North America�s fossil-fuel emissions in 2003 (1856 million metric tons of carbon � 10% with 95% certainty) were 27% of global emissions. Approximately 85% of those emissions were from the United States, 9% from Canada, and 6% from Mexico. The combustion of fossil fuels for commercial energy (primarily electricity) is the single largest contributor, accounting for approximately 42% of North American fossil emissions in 2003. Transportation is the second largest, accounting for 31% of total emissions. There are also globally important carbon sinks in North America. In 2003, growing vegetation in North America removed approximately 500 million tons of carbon per year (� 50%) from the atmosphere and stored it as plant material and soil organic matter. This land sink is equivalent to approximately 30% of the fossil-fuel emissions from North America. The imbalance between the fossil-fuel source and the sink on land is a net release to the atmosphere of 1350 million metric tons of carbon per year (� 25%). Approximately 50% of North America�s terrestrial sink is due to the regrowth of forests in the United States on former agricultural land that was last cultivated decades ago, and on timberland recovering from harvest. Other sinks are relatively small and not well quantified with uncertainties of 100% or more. The future of the North American terrestrial sink is also highly uncertain. The contribution of forest regrowth is expected to decline as the maturing forests grow more slowly and take up less carbon dioxide from the atmosphere. But, how regrowing forests and other sinks will respond to changes in climate and carbon dioxide concentration in the atmosphere is highly uncertain. The large difference between current sources and sinks and the expectation that the difference could become larger if the growth of fossil-fuel emissions continues and land sinks decline suggest that addressing imbalances in the North American carbon budget will likely require actions focused on reducing fossil-fuel emissions. Options to enhance sinks (growing forests or sequestering carbon in agricultural soils) can contribute, but enhancing sinks alone is likely insufficient to deal with either the current or future imbalance. Options to reduce emissions include efficiency improvement, fuel switching, and technologies such as carbon capture and geological storage. Implementing these options will likely require an array of policy instruments at local, regional, national, and international levels, ranging from the encouragement of voluntary actions to economic incentives, tradable emissions permits, and regulations. Meeting the demand for information by decision makers will likely require new modes of research characterized by close collaboration between scientists and carbon management stakeholders.
Purves, D. W., J W. Lichstein, and Stephen W. Pacala, 2007: Crown Plasticity and Competition for Canopy Space: A New Spatially Implicit Model Parameterized for 250 North American Tree Species. PLOS one, (9), doi:10.1371/journal.pone.0000870
[ Abstract ]
Background. Canopy structure, which can be defined as the sum of the sizes, shapes and relative placements of the tree crowns in a forest stand, is central to all aspects of forest ecology. But there is no accepted method for deriving canopy structure from the sizes, species and biomechanical properties of the individual trees in a stand. Any such method must capture the fact that trees are highly plastic in their growth, forming tessellating crown shapes that fill all or most of the canopy space. Methodology/Principal Findings. We introduce a new, simple and rapidly-implemented model�the Ideal Tree Distribution, ITD�with tree form (height allometry and crown shape), growth plasticity, and space-filling, at its core. The ITD predicts the canopy status (in or out of canopy), crown depth, and total and exposed crown area of the trees in a stand, given their species, sizes and potential crown shapes. We use maximum likelihood methods, in conjunction with data from over 100,000 trees taken from forests across the coterminous US, to estimate ITD model parameters for 250 North American tree species. With only two free parameters per species�one aggregate parameter to describe crown shape, and one parameter to set the so-called depth bias�the model captures between-species patterns in average canopy status, crown radius, and crown depth, and within-species means of these metrics vs stem diameter. The model also predicts much of the variation in these metrics for a tree of a given species and size, resulting solely from deterministic responses to variation in stand structure. Conclusions/Significance. This new model, with parameters for US tree species, opens up new possibilities for understanding and modeling forest dynamics at local and regional scales, and may provide a new way to interpret remote sensing data of forest canopies, including LIDAR and aerial photography.
Reuer, M. K., B. Barnett, Michael Bender, P. G. Falkowski, and M. B. Hendricks, 2007: New estimates of Southern Ocean biological production rates from O₂/Ar ratios and the triple isotope composition of O₂. Deep Sea Research I, 54(6), doi:10.1016/j.dsr.2007.02.007
[ Abstract ]
We report O₂/Ar ratios (a constraint on net community production) and the triple isotopic composition of dissolved O₂ (a constraint on gross primary production) in samples collected from the surface mixed layer on 23 Southern Ocean transits. Samples were collected at 1�2� meridional resolution during the austral summer. Methodological limitations notwithstanding, the results constrain the net/gross production ratio, net O₂ production, and gross O₂ production at unprecedented resolution throughout the Southern Ocean mixed layer. Gross O₂ production rates inferred from the oxygen triple isotopes are greater than production rates calculated from a model based on remotely sensed chlorophyll. This result agrees with previous ¹⁸O and ¹⁴C incubations along 170�W. O₂/Ar ratios exceeding saturation are consistently observed within the Subantarctic and Polar Frontal Zones south of New Zealand and Australia, showing that a net autotrophic community predominates during austral summer. Lower O₂/Ar values are observed within the Drake Passage and Antarctic Zone, suggesting unresolved influences of low net community production, net heterotrophy, and upwelling of O₂-undersaturated waters. In autotrophic waters of the austral summer mixed layer, ratios of net community production/gross O₂ production scatter about 0.13, corresponding to f ratios of �0.25. Net community/gross O₂ production ratios show no meridional gradient across the Antarctic Circumpolar Current, suggesting that an approximately constant fraction of gross primary productivity is regenerated or exported. Our calculated net O₂ production rates are in satisfactory agreement with comparable published estimates. Net and gross O₂ production rates are highest in the Subantarctic and decline to the south, paralleling the well-known trend of chlorophyll a concentrations. In an analysis of variance of net O₂ production and gross O₂ production with other environmental variables, the strongest correlations are between net O₂ production and sea surface temperature (SST) (direct correlation), climatological [NO₃] (inverse correlation), and estimates of primary productivity derived from a remote sensing (direct correlation). These trends are as expected if aerosol iron input is the most important influence on production. They are unexpected if upwelling-derived SiO₂ and iron are the leading influence or if lower SSTs promote greater export in this region.
Schneider, S. H., S. Semenov, A. Patwardhan, I. Burton, C.H.D. Magadza, Michael Oppenheimer, A. B. Pittock, A. Rahman, J. B. Smith, A. Suarez, and F. Yamin, 2007: Assessing Key Vulnerabilities and the Risk from Climate Change. Intergovernmental Panel on Climate Change, http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-chapter19.pdf, 19(Working Group II), 781-810
[ Abstract ]
Climate change will lead to changes in geophysical, biological and socio-economic systems.An impact describes a specific change in a system caused by its exposure to climate change. Impacts may be judged to be harmful or beneficial.Vulnerability to climate change is the degree to which these systems are susceptible to, and unable to cope with, adverse impacts. The concept of risk,which combines the magnitude of the impact with the probability of its occurrence, captures uncertainty in the underlying processes of climate change, exposure, impacts and adaptation. Many of these impacts, vulnerabilities and risks merit particular attention by policy-makers due to characteristics that might make them �key�. The identification of potential key vulnerabilities is intended to provide guidance to decision-makers for identifying levels and rates of climate change that may be associated with �dangerous anthropogenic interference� (DAI) with the climate system, in the terminology of United Nations Framework Convention on Climate Change (UNFCCC) Article 2. Ultimately, the definition of DAI cannot be based on scientific arguments alone, but involves other judgements informed by the state of scientific knowledge. No single metric can adequately describe the diversity of key vulnerabilities, nor determine their ranking.
Sheppard, M. C., and Robert H. Socolow, 2007: Perspective (Cover Story, Invited): Sustaining Fossil Fuel Use in a Carbon-Constrained World by Rapid Commercialization of Carbon Capture and Sequestration. AIChe Journal, Hoboken, NJ, John Wiley and Sons, 53(12), doi:10.1002/aic.11356 3022-3028
[ Abstract ]
Briefly stated, carbon capture and sequestration (CCS) will allow us to sustain many of the benefits of access to hydrocarbons even in a carbon constrained world. Even where the CO₂ generated by burning hydrocarbon cannot be captured easily (as in the case of oil use for transportation), sequestration of CO₂ from other sources (e.g., coal fired power stations) can help create, to some degree, the ��headroom�� needed to allow for the volumes of CO₂ which escape capture. Because of the likely continuing competitive (direct) cost of hydrocarbons, and in light of the huge investment already made in infrastructure to deliver them, the combination of fossil fuel use with CCS is likely to be emphasized as a strong complement to strategies involving alternative, nonhydrocarbon sources of energy supply. Moreover, concerns about the security of supply of transportation fuels are likely to drive moves toward less conventional hydrocarbon sources (coal-to-liquids, unconventional oil and gas, etc.). However, the exploitation of heavy oil, tar sands, oil shales, and liquids derived from coal for transportation fuel comes with a significantly heavier burden of CO₂ than is associated with conventional oil and gas. CCS has the potential to mitigate some of this extra CO₂ burden, provided it is implemented broadly over the coming decades. Widespread use could continue beyond the end of the century.
Sigman, Daniel, A. M. de Boer, and G. H. Haug, 2007: Antarctic stratification, atmospheric water vapor, and Heinrich events: A hypothesis for late Pleistocene deglaciations. AGU Geophysical Monograph, http://department.princeton.edu/geosciences/people/sigman/pdf/Sigman07_OCMI.pdf, 173, 335-350
[ Abstract ]
We have previously argued that the Antarctic and subarctic North Pacific are stratified during ice ages, causing to a large degree the observed low CO₂ levels of ice age atmospheres by sequestering respired CO₂ in the ocean abyss. Here, we suggest a mechanism for the major deglaciations of the late Pleistocene. The mechanism begins with freshwater discharge to the North Atlantic, as evidenced by a Heinrich event, that shuts down North Atlantic overturning. Because of a global requirement for deep ocean ventilation, the North Atlantic shutdown drives overturning in the Antarctic, which, in turn, releases CO₂ to the atmosphere and reduces Antarctic sea ice extent. The resulting increase in atmospheric CO₂ and decrease in albedo then drive global warming and deglaciation. As a control on the timing of deglaciations, we look to the sensitivity of atmospheric freshwater transport to low latitude temperature, which is a natural antagonist to Antarctic stratification under cold climates. While Antarctic stratification is proposed to develop early in a glacial period, continued cooling through the glacial period may reduce the poleward atmospheric freshwater transport and thus may prepare the Antarctic halocline for collapse. Deglaciations may coincide with obliquity maxima because a reduced low-to-high latitude insolation gradient decreases the net poleward freshwater transport and perhaps also because increased polar insolation can warm the deep ocean and shift the westerly winds poleward, all of which should work to weaken Antarctic stratification. Precession minima may encourage Antarctic destratification by biasing tropical water vapor transport toward the northern hemisphere. Finally, obliquity and precession may work together to encourage the circum-North Atlantic freshwater discharge event that initiates the deglacial sequence.
Socolow, Robert H., January 2007: Facing new unknowns. Bulletin of the Atomic Scientists, Chicago, IL, Bulletin of the Atomic Scientists, 63(1), doi:10.2968/063001014 45-46
[ Abstract ]
THE BULLETIN'S ICONIC CLOCK CAPTURES more than the imminence of catastrophe. It signifies the transformative power of science, a planetary consciousness, and the ironies of moral behavior. All of these messages are of first-order importance in grappling with climate change.
Socolow, Robert H., and S. H. Lam, 2007: Good Enough Tools for Global Warming Policy Making. Philosophical Transactions of the Royal Society, 365, doi:10.1098/rsta.2006.1961 897-934
[ Abstract ]
We present a simple analysis of the global warming problem caused by the emissions of CO₂ (a major greenhouse gas) into the atmosphere resulting from the burning of fossil fuels. We provide quantitative tools which enable policymakers and interested citizens to explore the following issues central to the global warming problem. (i) At what rate are we permitted to continue to emit CO₂ after the global average atmospheric concentration has �stabilized� at some chosen target level? The answer here provides the magnitude of the effort, measured by the necessary total reduction of today�s global (annual) emissions rate to achieve stabilization. We shall see that stabilized emissions rates for all interesting stabilized concentration levels are much lower than the current emissions rate, but these small finite values are very important. (ii) Across how many years can we spread the total effort to reduce the annual CO₂ emissions rate from its current high value to the above-mentioned low and stabilized target value? The answer here provides the time-scale of the total mitigation effort for any chosen atmospheric concentration target level. We confirm the common understanding that targets below a doubling of the pre-industrial concentration create great pressure to produce action immediately, while targets above double the pre-industrial level can tolerate longer periods of inaction. (iii) How much harder is the future mitigation effort, if we do not do our share of the job now? Is it a good idea to overshoot a stabilization target? The quantitative answers here provide the penalty of procrastination. For example, the mitigation task to avoid doubling the pre-industrial level is a problem that can be addressed gradually, over a period extending more than a century, if started immediately, but procrastination can turn the effort into a much more urgent task that extends over only a few decades. We also find that overshooting target levels is a bad idea. The quality of public discourse on this subject could be much enhanced if ball-park quantitative answers to these questions were more widely known.
Socolow, Robert H., 2007: Invited Foreword: CCS Technology: Ready to Go. Fundamentals of Carbon Capture and Storage Technology, The Petroleum Economist Ltd, Playhouse Yard, London, http://clients.digipage.co.uk/?userpath=00000049/00008053/00025360/&page=7, (ISBN: 1 86186 277 6), 4-9
[ Abstract ]
The heightened concern for climate change and the greater competitiveness of coal are on a collision course. To have a material effect, many hundreds of projects will be necessary.
Sweeney, C., M. N. Gloor, A. R. Jacobson, R. M. Key, G. McKinley, Jorge Sarmiento, and R. Wanninkhof, 2007: Constraining global air-sea gas exchange for CO₂ with recent bomb ¹⁴C measurements. Global Biogeochemical Cycles, 21(GB2015), doi:10.1029/2006GB002784
[ Abstract ]
The ¹⁴CO₂ released into the stratosphere during bomb testing in the early 1960s provides a global constraint on air-sea gas exchange of soluble atmospheric gases like CO₂. Using the most complete database of dissolved inorganic radiocarbon, DI¹⁴C, available to date and a suite of ocean general circulation models in an inverse mode we recalculate the ocean inventory of bomb-produced DI¹⁴C in the global ocean and confirm that there is a 25% decrease from previous estimates using older DI¹⁴C data sets. Additionally, we find a 33% lower globally averaged gas transfer velocity for CO₂ compared to previous estimates (Wanninkhof, 1992) using the NCEP/NCAR Reanalysis 1 1954�2000 where the global mean winds are 6.9 m s^-1. Unlike some earlier ocean radiocarbon studies, the implied gas transfer velocity finally closes the gap between small-scale deliberate tracer studies and global-scale estimates. Additionally, the total inventory of bomb-produced radiocarbon in the ocean is now in agreement with global budgets based on radiocarbon measurements made in the stratosphere and troposphere. Using the implied relationship between wind speed and gas transfer velocity ks = 0.27u²₁₀ 2 i(Sc/660)^-0.5 and standard partial pressure difference climatology of CO₂ we obtain an net air-sea flux estimate of 1.3 � 0.5 PgCyr^-1 for 1995. After accounting for the carbon transferred from rivers to the deep ocean, our estimate of oceanic uptake (1.8 � 0.5 PgCyr^-1) compares well with estimates based on ocean inventories, ocean transport inversions using ocean concentration data, and model simulations.
Yancheva, G., N. R. Nowaczyk, J. Mingram, P. Dulski, G. Schettler, F. W. Negendank, J. Liu, Daniel Sigman, L. C. Peterson, and G. H. Haug, 2007: Influence of the Intertropical Convergence Zone on the East Asian Monsoon. Nature, 445, doi:10.1038/nature05431 74-77
[ Abstract ]
The Asian�Australian monsoon is an important component of the Earth�s climate system that influences the societal and economic activity of roughly half the world�s population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the B�lling�Aller�d warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period AD 700 to 900, suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.
Yang, C.-J., and Michael Oppenheimer, 2007: A �Manhattan Project� for Climate Change? Climatic Change, 80(3-4), doi:10.1007/S10584-006-9202-7 199-204
[ Abstract ]
Climate change is a chronic yet unprecedented threat to civilization. Large scale abatement of greenhouse-gas emissions would require not only replacing carbon-intensive fuels (like coal and oil) with low-emission or carbon-free energy alternatives, but also replacing much of the infrastructure that uses primary and secondary energy. As a political issue, the scale of the problem makes carbon mitigation unique and difficult to resolve. Its chronic nature is another obstacle to implementation of policy in the near term. It would take decades to displace fossil fuels even if the technologies to do so were available. Furthermore, disagreement has arisen on whether currently available technologies are sufficient to significantly reduce emissions over the next several decades (Pacala and Socolow 2004; Hoffert et al. 2002). The notion of developing new technologies before mandating emissions reductions has gained currency in response to these complexities. The Bush Administration climate policy favors this line of thinking, rejecting any Kyoto-style arrangement involving mandatory targets and proposing the development of new technologies as an alternative (Bush 2005). Here we argue that such approaches are based on the misconception that innovations needed for carbon mitigation can be effectively and efficiently developed without carbon regulations.
Battle, M., S. E. Mikaloff-Fletcher, Michael Bender, R. F. Keeling, A. C. Manning, N. Gruber, P. P. Tans, M. B. Hendricks, D. T. Ho, C. Simonds, R. Mika, and B. Paplawsky, 2006: Atmospheric potential oxygen: New observations and their implications for some atmospheric and oceanic models. Global Biogeochemical Cycles, 20(GB1010), doi:10.1029/2005GB002534
[ Abstract ]
Measurements of atmospheric O₂/N₂ ratios and CO₂ concentrations can be combined into a tracer known as atmospheric potential oxygen (APO ≈ O₂/N₂ + CO₂) that is conservative with respect to terrestrial biological activity. Consequently, APO reflects primarily ocean biogeochemistry and atmospheric circulation. Building on the work of Stephens et al. (1998), we present a set of APO observations for the years 1996�2003 with unprecedented spatial coverage. Combining data from the Princeton and Scripps air sampling programs, the data set includes new observations collected from ships in the low-latitude Pacific. The data show a smaller interhemispheric APO gradient than was observed in past studies, and different structure within the hemispheres. These differences appear to be due primarily to real changes in the APO field over time. The data also show a significant maximum in APO near the equator. Following the approach of Gruber et al. (2001), we compare these observations with predictions of APO generated from ocean O₂ and CO₂ flux fields and forward models of atmospheric transport. Our model predictions differ from those of earlier modeling studies, reflecting primarily the choice of atmospheric transport model (TM3 in this study). The model predictions show generally good agreement with the observations, matching the size of the interhemispheric gradient, the approximate amplitude and extent of the equatorial maximum, and the amplitude and phasing of the seasonal APO cycle at most stations. Room for improvement remains. The agreement in the interhemispheric gradient appears to be coincidental; over the last decade, the true APO gradient has evolved to a value that is consistent with our time-independent model. In addition, the equatorial maximum is somewhat more pronounced in the data than the model. This may be due to overly vigorous model transport, or insufficient spatial resolution in the air-sea fluxes used in our modeling effort. Finally, the seasonal cycles predicted by the model of atmospheric transport show evidence of an excessive seasonal rectifier in the Aleutian Islands and smaller problems elsewhere.
Behrenfeld, M. J., R. T. O'Malley, D. A. Siegel, C. R. McClain, Jorge Sarmiento, G. C. Feldman, A. J. Milligan, P. G. Falkowski, R. M. Letelier, and E. S. Boss, 2006: Climate driven trends in contemporary ocean productivity. Nature, 444, doi:10.1038/nature05317 752-755
[ Abstract ]
Contributing roughly half of the biosphere�s net primary production (NPP), photosynthesis by oceanic phytoplankton is a vital link in the cycling of carbon between living and inorganic stocks. Each day, more than a hundred million tons of carbon in the form of CO₂ are fixed into organic material by these ubiquitous, microscopic plants of the upper ocean, and each day a similar amount of organic carbon is transferred into marine ecosystems by sinking and grazing. The distribution of phytoplankton biomass and NPP is defined by the availability of light and nutrients (nitrogen, phosphate, iron). These growth-limiting factors are in turn regulated by physical processes of ocean circulation, mixed-layer dynamics, upwelling, atmospheric dust deposition, and the solar cycle. Satellite measurements of ocean colour provide a means of quantifying ocean productivity on a global scale and linking its variability to environmental factors. Here we describe global ocean NPP changes detected from space over the past decade. The period is dominated by an initial increase in NPP of 1,930 teragrams of carbon a year (Tg C yr ^-1 ), followed by a prolonged decrease averaging 190 Tg C yr ^-1 . These trends are driven by changes occurring in the expansive stratified low-latitude oceans and are tightly coupled to coincident climate variability. This link between the physical environment and ocean biology functions through changes in upper-ocean temperature and stratification, which influence the availability of nutrients for phytoplankton growth. The observed reductions in ocean productivity during the recent post-1999 warming period provide insight on how future climate change can alter marine food webs.
Bohlman, S. A., and S. T. O'Brien, 2006: Allometry, adult stature and regeneration requirement of 65 species on Barro Colorado Island, Panama. Journal of Tropical Ecology, 22(02), doi:10.1017/S0266467405003019 123-136
[ Abstract ]
This study provides a community-level analysis of how regeneration requirement and adult stature are related to tree allometry (diameter, height and crown size) throughout post-seedling ontogeny on Barro Colorado Island, Panama. Comparing 65 species, gap species are taller, have higher diameter growth rates and occupy more low-canopy sites (≤10m canopy height) than shade species at small diameters (≤10 cm dbh). For trees >10 cm dbh, diameter-height relationships and growth rates no longer differ between gap and shade species, but shade species have larger, particularly deeper, crowns than gap species. Species with tall adult stature have more slender stems with larger crowns compared with treelet and mid-canopy species starting at 5 cmdbh. From 10 to 40 cm dbh, diameter growth rate is also significantly greater for tall species. The consistent allometric differences between functional groups on a community level will, in part, determine vertical and horizontal stand structure.
Crevoisier, C., M. N. Gloor, E. Gloaguen, L. W. Horowitz, Jorge Sarmiento, C. Sweeney, and P. P. Tans, 2006: A direct carbon budgeting approach to infer carbon sources and sinks. Design and synthetic application to complement the NACP observation network. Tellus, 58(5), doi:10.1111/j.1600-0889.2006.00214.x 366-375
[ Abstract ]
In order to exploit the upcoming regular measurements of vertical carbon dioxide (CO₂) profiles over North America implemented in the framework of the North American Carbon Program (NACP), we design a direct carbon budgeting approach to infer carbon sources and sinks over the continent using model simulations. Direct budgeting puts a control volume on top of North America, balances air mass in- and outflows into the volume and solves for the surface fluxes. The flows are derived from the observations through a geostatistical interpolation technique called Kriging combined with transport fields from weather analysis. The use of CO₂ vertical profiles simulated by the atmospheric transport model MOZART-2 at the planned 19 stations of the NACP network has given an estimation of the error of 0.39 GtC yr^-1 within the model world. Reducing this error may be achieved through a better estimation of mass fluxes associated with convective processes affecting North America. Complementary stations in the north-west and the north-east are also needed to resolve the variability of CO₂ in these regions. For instance, the addition of a single station near 52�N; 110�W is shown to decrease the estimation error to 0.34 GtC yr^-1.
De Lorenzo, L., and Robert H. Socolow, June 2006: Modeling Technology Choice under Alternative CO₂ Policies. Proceedings of the 8th International Conference on Greenhouse Gas Control Technologies (GHGT-8),
[ Abstract ]
Our work addresses the interaction between CO₂ policy and coal technology over the next 25 years. Coal power is a particularly attractive sector from which to seek CO₂ emission reductions because the emissions are from large point sources and several strategies are available to lower emissions. The electric industry currently contributes approximately 40% of global CO₂ emissions, and the coal electric industry about 30% of global CO₂ emissions. We develop a linear programming formalism that allows a high-level analysis of three kinds of competition: 1) between several kinds of new coal plants with and without CO₂ capture, each becoming more efficient and cheaper over time; 2) between retiring old coal plants, retrofitting them and constructing new ones; and 3) between building CO₂ capture capability into a new coal plant in two stages (the first stage being a �capture-ready� plant) and building the capability all at once. These competitions are examined under three matched pairs of trajectories of the CO₂ tax that result in three tax levels in 2030 ($100/tC, $200/tC and $300/tC): �sudden-change,� where the tax is increased suddenly at around 2020, and �gradual-change,� where the tax is increased gradually from 2005 to 2030 (fig.1). We find that: i) a �sudden-change� carbon tax induces more retrofitting of vintage plants than a policy with �gradual-change�; ii) all retrofit options considered appear at least once in the scenarios explored; iii) the case for capture-ready plants is weak with current cost numbers available from literature.
Delworth, T. L., A. J. Broccoli, A. Rosati, R. J. Stouffer, V. Balaji, J. A. Beesley, W. F. Cooke, K. W. Dixon, J. P. Dunne, K. A. Dunne, J. Durachta, and K. L. Findell, et al., 2006: GFDL�s CM2 Global Coupled Climate Models. Part 1: Formulation and Simulation Characteristics. Journal of Climate, 19, doi:10.1175/JCLI3629.1 643-674
[ Abstract ]
The formulation and simulation characteristics of two new global coupled climate models developed at NOAA�s Geophysical Fluid Dynamics Laboratory (GFDL) are described. The models were designed to simulate atmospheric and oceanic climate and variability from the diurnal time scale through multicentury climate change, given our computational constraints. In particular, an important goal was to use the same model for both experimental seasonal to interannual forecasting and the study of multicentury global climate change, and this goal has been achieved.
Two versions of the coupled model are described, called CM2.0 and CM2.1. The versions differ primarily in the dynamical core used in the atmospheric component, along with the cloud tuning and some details of the land and ocean components. For both coupled models, the resolution of the land and atmospheric components is 2� latitude X 2.5� longitude; the atmospheric model has 24 vertical levels. The ocean resolution is 1� in latitude and longitude, with meridional resolution equatorward of 30� becoming progressively finer, such that the meridional resolution is 1/3� at the equator. There are 50 vertical levels in the ocean, with 22 evenly spaced levels within the top 220 m. The ocean component has poles over North America and Eurasia to avoid polar filtering. Neither coupled model employs flux adjustments.
The control simulations have stable, realistic climates when integrated over multiple centuries. Both models have simulations of ENSO that are substantially improved relative to previous GFDL coupled models. The CM2.0 model has been further evaluated as an ENSO forecast model and has good skill (CM2.1 has not been evaluated as an ENSO forecast model). Generally reduced temperature and salinity biases exist in CM2.1 relative to CM2.0. These reductions are associated with 1) improved simulations of surface wind stress in CM2.1 and associated changes in oceanic gyre circulations; 2) changes in cloud tuning and the land model, both of which act to increase the net surface shortwave radiation in CM2.1, thereby reducing an overall cold bias present in CM2.0; and 3) a reduction of ocean lateral viscosity in the extratropics in CM2.1, which reduces sea ice biases in the North Atlantic.
Both models have been used to conduct a suite of climate change simulations for the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment report and are able to simulate the main features of the observed warming of the twentieth century. The climate sensitivities of the CM2.0 and CM2.1 models are 2.9 and 3.4 K, respectively. These sensitivities are defined by coupling the atmospheric components of CM2.0 and CM2.1 to a slab ocean model and allowing the model to come into equilibrium with a doubling of atmospheric CO₂. The output from a suite of integrations conducted with these models is freely available online (see http://nomads.gfdl.noaa.gov/).
Greenblatt, J. B., Robert H. Socolow, and K. Riahi, June 2006: Wedge decomposition analysis: Application to SRES and Post-SRES Scenarios. Proceedings of the 8th International Conference on Greenhouse Gas Control Technologies (GHGT-8),
[ Abstract ]
We introduce a general methodology for displaying the gross assumptions behind any carbon emissions trajectory, relative to a reference trajectory, and we apply this methodology to a limited number of IPCC SRES scenarios [1]. These scenarios have been used widely for climate change analysis. We examine four scenarios (A1B, A2, B1, B2) together with three paired "post-SRES" scenarios [2, 3] that achieve CO₂ stabilization at 550 ppm by 2100. Our analysis is guided by the concept of the "stabilization wedge" introduced in a recent paper by Pacala and Socolow [4], which measures the quantitative contributions of specific technologies and strategies over the next 50 years in units of 1 GtC/yr reductions in 2050. We find that autonomous carbon-emissions reduction activity in the SRES scenarios account for a large number of "virtual" wedges, ranging from 8 to 35 in 2050. Roughly half of the virtual wedges in each scenario is due to energy efficiency improvements and structural change in the economy; most of the remaining half is due to high penetrations of non-fossil energy technologies. Post-SRES scenarios require only 2 to 4 "real" wedges in 2050, accounted for largely by greater non-fossil energy, greater energy efficiency, and CO₂ sequestration. Our results reveal that the SRES and post-SRES scenarios share a number of common assumptions. In particular we find that the baseline development path, i.e., the number of virtual wedges and "autonomous" trends in absence of any climate policies, play a central role in determining the mitigation effort needed for achieving climate stabilization.
Guo, Z., P. A. Dirmeyer, R. D. Koster, G. Bonan, E. Chan, P. Cox, C. T. Gordon, S. Kanae, E. Kowalczyk, D. Lawrence, P. Liu, C.-H. Lu, and S. Malyshev, et al., 2006: GLACE: The Global Land-Atmosphere Coupling Experiment. 2. Analysis In , 7, doi:10.1175/JHM511.1 611-625
[ Abstract ]
The 12 weather and climate models participating in the Global Land�Atmosphere Coupling Experiment (GLACE) show both a wide variation in the strength of land�atmosphere coupling and some intriguing commonalities. In this paper, the causes of variations in coupling strength�both the geographic variations within a given model and the model-to-model differences�are addressed. The ability of soil moisture to affect precipitation is examined in two stages, namely, the ability of the soil moisture to affect evaporation, and the ability of evaporation to affect precipitation. Most of the differences between the models and within a given model are found to be associated with the first stage�an evaporation rate that varies strongly and consistently with soil moisture tends to lead to a higher coupling strength. The first-stage differences reflect identifiable differences in model parameterization and model climate. Intermodel differences in the evaporation� precipitation connection, however, also play a key role.
Hurtt, G. C., S. Frolking, M. G. Fearon, B. Moore III, E. Shevliakova, S. Malyshev, Stephen W. Pacala, and R. A. Houghton, 2006: The underpinnings of land-use history: three centuries of global gridded landuse transitions, wood-harvest activity, and resulting secondary lands. Global Change Biology, 12(7), doi:10.1111/j.1365-2486.2006.01150.x 1208-1299
[ Abstract ]
To accurately assess the impacts of human land use on the Earth system, information is needed on the current and historical patterns of land-use activities. Previous global studies have focused on developing reconstructions of the spatial patterns of agriculture. Here, we provide the first global gridded estimates of the underlying land conversions (land-use transitions), wood harvesting, and resulting secondary lands annually, for the period 1700�2000. Using data-based historical cases, our results suggest that 42�68% of the land surface was impacted by land-use activities (crop, pasture, wood harvest) during this period, some multiple times. Secondary land area increased 10�44 X 10⁶km²; about half of this was forested. Wood harvest and shifting cultivation generated 70�90% of the secondary land by 2000; permanent abandonment and relocation of agricultural land accounted for the rest. This study provides important new estimates of globally gridded land-use activities for studies attempting to assess the consequences of anthropogenic changes to the Earth�s surface over time.
Jin, X., N. Gruber, J. P. Dunne, Jorge Sarmiento, and R. A. Armstrong, 2006: Diagnosing the contribution of phytoplankton functional groups to the production and export of particulate organic carbon, CaCO₃, and opal from global nutrient and alkalinity distributions. Global Biogeochemical Cycles, 20(GB2015), doi:10.1029/2005GB002532
[ Abstract ]
We diagnose the contribution of four main phytoplankton functional groups to the production and export of particulate organic carbon (POC), CaCO₃, and opal by combining in a restoring approach global oceanic observations of nitrate, silicic acid, and alkalinity with a simple size-dependent ecological/biogeochemical model. In order to determine the robustness of our results, we employ three different variants of the ocean general circulation model (OGCM) required to transport and mix the nutrients and alkalinity into the upper ocean. In our standard model, the global export of CaCO₃ is diagnosed as 1.1 PgC yr^-1 (range of sensitivity cases 0.8 to 1.2 PgC yr^-1) and that of opal as 180 Tmol Si yr^-1 (range 160 to 180 Tmol Si yr^-11). CaCO₃ export is found to have three maxima at approximately 40�S, the equator, and around 40�N. In contrast, the opal export is dominated by the Southern Ocean with a single maximum at around 60�S. The molar export ratio of inorganic to organic carbon is diagnosed in our standard model to be about 0.09 (range 0.07 to 0.10) and found to be remarkably uniform spatially. The molar export ratio of opal to organic nitrogen varies substantially from values around 2 to 3 in the Southern Ocean south of 45�S to values below 0.5 throughout most of the rest of the ocean, except for the North Pacific. Irrespective of which OGCM is used, large phytoplankton dominate the export of POC, with diatoms alone accounting for 40% of this export, while the contribution of coccolithophorids is only about 10%. Small phytoplankton dominate net primary production (NPP) with a fraction of ≈70%. Diatoms and coccolithophorids account for about 15% and less than 2% of NPP, respectively. These diagnosed contributions of the main phytoplankton functional groups to NPP are also robust across all OGCMs investigated. Correlation and regression analyses reveal that the variations in the relative contributions of diatoms and coccolithophorids to NPP can be predicted reasonably well on the basis of a few key parameters.
Koster, R. D., Z. Guo, P. A. Dirmeyer, G. Bonan, E. Chan, P. Cox, H. Davies, C. T. Gordon, S. Kanae, E. Kowalczyk, D. Lawrence, and P. Liu, et al., 2006: GLACE: The Global Land-Atmosphere Coupling Experiment. 1. Overview. Journal of Hydrometeorology, 7, doi:10.1175/JHM510.1 590-610
[ Abstract ]
The Global Land�Atmosphere Coupling Experiment (GLACE) is a model intercomparison study focusing on a typically neglected yet critical element of numerical weather and climate modeling: land� atmosphere coupling strength, or the degree to which anomalies in land surface state (e.g., soil moisture) can affect rainfall generation and other atmospheric processes. The 12 AGCM groups participating in GLACE performed a series of simple numerical experiments that allow the objective quantification of this element for boreal summer. The derived coupling strengths vary widely. Some similarity, however, is found in the spatial patterns generated by the models, with enough similarity to pinpoint multimodel �hot spots� of land�atmosphere coupling. For boreal summer, such hot spots for precipitation and temperature are found over large regions of Africa, central North America, and India; a hot spot for temperature is also found over eastern China. The design of the GLACE simulations are described in full detail so that any interested modeling group can repeat them easily and thereby place their model�s coupling strength within the broad range of those documented here.
Kunkel, C., R. Hallberg, and Michael Oppenheimer, 2006: Coral Reefs Reduce Tsunami Impact in Model Simulations. Geophysical Research Letters, 33(L23612), doi:10.1029/2006GL027892
[ Abstract ]
Significant buffering of the impact of tsunamis by coral reefs is suggested by limited observations and some anecdotal reports, particularly following the 2004 Indian Ocean tsunami. Here we simulate tsunami run-up on idealized topographies in one and two dimensions using a nonlinear shallow water model and show that a sufficiently wide barrier reef within a meter or two of the surface reduces run-up on land on the order of 50%. We studied topographies representative of volcanic islands (islands with no continental shelf) but our conclusions may pertain to other topographies. Effectiveness depends on the amplitude and wavelength of the incident tsunami, as well as the geometry and health of the reef and the offshore distance of the reef. Reducing the threat to reefs from anthropogenic nutrients, sedimentation, fishing practices, channelbuilding, and global warming would help to protect some islands against tsunamis.
Laurian, A., A. Lazar, G. Reverdin, K. B. Rodgers, and P. Terray, 2006: Poleward propagation of spiciness anomalies in the North Atlantic Ocean. Geophysical Research Letters, 33(L13603), doi:10.1029/2006GL026155
[ Abstract ]
Recent modelling results suggest that subsurface salinity anomalies propagating from the tropics can reach and precondition the deep-water formation regions, thus modulating the THC variability. The forcing and propagative aspects of this mechanism are presented in the North Atlantic Ocean over 1948 -2002 using an OGCM. Density compensated salinity anomalies of 0.1 up to 0.35 psu along σ = 26 kg.m^-3 are generated in the salinity maximum region at interannual to decadal frequency. The relation between subsurface conditions and late winter sea surface salinity variability supports the subduction mechanism. They circulate over isopycnals ranging from 25.6 σ to 26.2 σ at current speed between 150 m and 250 m depth toward Cape Hatteras via the Gulf of Mexico on a typical 6-year transit. Although mixing along the pathway reduces the amplitude of salinity anomalies by about 66%, they largely determine the subsurface spiciness of the Gulf Stream up to 30�N, upstream of the outcrop region.
Lin, Li-Hung, P.-L. Wang, D. Rumble, J. Lippmann-Pipke, E. Boice, L. Pratt, B. S. Lollar, E. L. Brodie, T. C. Hazen, G. L. Andersen, T. Z. DeSantis, D. Moser, D. Kershaw, and T. C. Onstott, 2006: Long term biosustainability in a high energy, low diversity crustal biome In , 314, doi:10.1126/science.1127376 479-482
[ Abstract ]
Geochemical, microbiological, and molecular analyses of alkaline saline groundwater at 2.8 kilometers depth in Archaean metabasalt revealed a microbial biome dominated by a single phylotype affiliated with thermophilic sulfate reducers belonging to Firmicutes. These sulfate reducers were sustained by geologically produced sulfate and hydrogen at concentrations sufficient to maintain activities for millions of years with no apparent reliance on photosynthetically derived substrates.
Marinov, I., A. Gnanadesikan, J. R. Toggweiler, and Jorge Sarmiento, 2006: The Southern Ocean biogeochemical divide. Nature, 441, doi:10.1038/nature04883 964-967
[ Abstract ]
Modeling studies have demonstrated that the nutrient and carbon cycles in the Southern Ocean play a central role in setting the air-sea balance of CO₂ and global biological production. Box model studies first pointed out that an increase in nutrient utilization in the high latitudes results in a strong decrease in the atmospheric carbon dioxide partial pressure (pCO₂ ). This early research led to two important ideas: high latitude regions are more important in determining atmospheric (pCO₂ than low latitudes, despite their much smaller area, and nutrient utilization and atmospheric (pCO₂ are tightly linked. Subsequent general circulation model simulations show that the Southern Ocean is the most important high latitude region in controlling preindustrial atmospheric CO₂ because it serves as a lid to a larger volume of the deep ocean. Other studies point out the crucial role of the Southern Ocean in the uptake and storage of anthropogenic carbon dioxide and in controlling global biological production. Here we probe the system to determine whether certain regions of the Southern Ocean are more critical than others for air-sea CO₂ balance and the biological export production, by increasing surface nutrient drawdown in an ocean general circulation model. We demonstrate that atmospheric CO₂ and global biological export production are controlled by different regions of the Southern Ocean. The air�sea balance of carbon dioxide is controlled mainly by the biological pump and circulation in the Antarctic deep-water formation region, whereas global export production is controlled mainly by the biological pump and circulation in the Subantarctic intermediate and mode water formation region. The existence of this biogeochemical divide separating the Antarctic from the Subantarctic suggests that it may be possible for climate change or human intervention to modify one of these without greatly altering the other.
Mignone, B. K., A. Gnanadesikan, Jorge Sarmiento, and R. D. Slater, 2006: Central role of southern hemisphere winds and eddies in modulating the oceanic uptake of anthropogenic carbon. Geophysical Research Letters, 33(L01604), doi:10.1029/2005GL024464
[ Abstract ]
Although the world ocean is known to be a major sink of anthropogenic carbon dioxide, the exact processes governing the magnitude and regional distribution of carbon uptake remain poorly understood. Here we show that Southern Hemisphere winds, by altering the Ekman volume transport out of the Southern Ocean, strongly control the regional distribution of anthropogenic uptake in an ocean general circulation model, while winds and isopycnal thickness mixing together, by altering the volume of light, actively-ventilated ocean water, exert strong control over the absolute magnitude of anthropogenic uptake. These results are provocative in suggesting that climate-mediated changes in pycnocline volume may ultimately control changes in future carbon uptake.
Mikaloff-Fletcher, S. E., N. Gruber, A. R. Jacobson, S. C. Doney, S. Dutkiewicz, M. Gerber, M. Follows, F. Joos, K. Lindsay, D. Menemenlis, A. Mouchet, S. A. M�ller, and Jorge Sarmiento, 2006: Inverse estimates of anthropogenic CO₂ uptake, transport, and storage by the ocean. Global Biogeochemical Cycles, 20(GB2002), doi:10.1029/2005GB002530
[ Abstract ]
Regional air-sea fluxes of anthropogenic CO₂ are estimated using a Green�s function inversion method that combines data-based estimates of anthropogenic CO₂ in the ocean with information about ocean transport and mixing from a suite of Ocean General Circulation Models (OGCMs). In order to quantify the uncertainty associated with the estimated fluxes owing to modeled transport and errors in the data, we employ 10 OGCMs and three scenarios representing biases in the data-based anthropogenic CO₂ estimates. On the basis of the prescribed anthropogenic CO₂ storage, we find a global uptake of 2.2 � 0.25 Pg C yr^-1, scaled to 1995. This error estimate represents the standard deviation of the models weighted by a CFC-based model skill score, which reduces the error range and emphasizes those models that have been shown to reproduce observed tracer concentrations most accurately. The greatest anthropogenic CO₂ uptake occurs in the Southern Ocean and in the tropics. The flux estimates imply vigorous northward transport in the Southern Hemisphere, northward cross-equatorial transport, and equatorward transport at high northern latitudes. Compared with forward simulations, we find substantially more uptake in the Southern Ocean, less uptake in the Pacific Ocean, and less global uptake. The large-scale spatial pattern of the estimated flux is generally insensitive to possible biases in the data and the models employed. However, the global uptake scales approximately linearly with changes in the global anthropogenic CO₂ inventory. Considerable uncertainties remain in some regions, particularly the Southern Ocean.
Moorcroft, P. R., Stephen W. Pacala, and M. A. Lewis, 2006: Potential role of natural enemies during tree range expansions following climate change. Journal of Theoretical Biology, 241(3), doi:10.1016/j.jtbi.2005.12.019 601-616
[ Abstract ]
Recent investigations have shown how chance, long-range dispersal events can allow tree populations to migrate rapidly in response to changes in climate. However, this apparent solution to Reid�s paradox applies solely within the context of single species models, while the rapid migration rates seen in pollen records occurred within multispecies communities. Ecologists are therefore presented with a new challenge: reconciling the macroscopic dynamics of spread seen in the pollen record with the rules and interactions governing plant community assembly. A case that highlights this issue is the rapid spread of Beech during the Holocene into a landscape already dominated by a close competitor, Hemlock. In this study, we analyse a simple model of plant community assembly incorporating competition for space and dispersal dynamics, showing how, even when a species is capable of rapid migration into an empty landscape, the presence of an ecologically similar competitor causes Reid�s paradox to re-emerge because of the dramatic slowing effect of competitive interactions on a species� rate of spread. We then show how the answer to the question of how tree species dispersed rapidly into occupied landscapes may lie in secondary interactions with host-specific pathogens and parasites. Inclusion of host-specific pathogens into the simple community assembly model illustrates how tree species undergoing range expansions can temporarily outstrip specialist predators, giving rise to a transient Jansen�Connell effect, in which the invader acts as temporary �super-species� that spreads rapidly into communities already occupied by competitors at rates consistent with those observed in the paleo-record.
Muller-Landau, H. C., R. C. Condit, J. Chave, S. C. Thomas, S. A. Bohlman, S. Bunyavejchewin, S. Davies, R. Foster, S. Gunatilleke, N. Gunatilleke, K. E. Harms, and T. Hart, et al., 2006: Testing metabolic ecology theory for allometric scaling of tree size, growth, and mortality in tropical forests. Ecology Letters, 9(5), doi:10.1111/j.1461-0248.2006.00904.x 575-588
[ Abstract ]
The theory of metabolic ecology predicts specific relationships among tree stem diameter, biomass, height, growth and mortality. As demographic rates are important to estimates of carbon fluxes in forests, this theory might offer important insights into the global carbon budget, and deserves careful assessment. We assembled data from 10 oldgrowth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to test the theory�s predictions. We also developed a set of alternative predictions that retained some assumptions of metabolic ecology while also considering how availability of a key limiting resource, light, changes with tree size. Our results show that there are no universal scaling relationships of growth or mortality with size among trees in tropical forests. Observed patterns were consistent with our alternative model in the one site where we had the data necessary to evaluate it, and were inconsistent with the predictions of metabolic ecology in all forests.
Naegler, T., P. Ciais, K. B. Rodgers, and I. Levin, 2006: Excess radiocarbon constraints on air-sea gas exchange and the uptake of CO₂ by the oceans. Geophysical Research Letters, 33(L11802), doi:10.1029/2005GL025408
[ Abstract ]
We re-assess the constraints that estimates of the global ocean excess radiocarbon inventory (I^E) place on air-sea gas exchange. We find that the gas exchange scaling parameter aq cannot be constrained by I^E alone. Non-negligible biases in different global wind speed data sets require a careful adaptation of a_q to the wind field chosen. Furthermore, aq depends on the spatial and temporal resolution of the wind fields. We develop a new wind speed-and inventory-normalized gas exchange parameter a_q^N which takes into account these biases and which is easily adaptable to any new estimate of I^E. Our study yields an average estimate of a_q of 0.32 � 0.05 for monthly mean winds, lower than the previous estimate (0.39) from Wanninkhof (1992). We calculate a global annual average piston velocity for CO₂ of 16.7 � 2.9 cm/hr and a gross CO₂ flux between atmosphere and ocean of 73 � 10 PgC/yr, significantly lower than results from previous studies.
Naik, V., D. L. Mauzerall, L. W. Horowitz, M. D. Schwarzkopf, V. Ramaswamy, and Michael Oppenheimer, 2006: Net radiative forcing due to changes in regional emissions of tropospheric ozone precursors. Journal of Geophysical Research, 110(D24306), doi:10.1029/2005JD005908
[ Abstract ]
The global distribution of tropospheric ozone (O₃) depends on the emission of precursors, chemistry, and transport. For small perturbations to emissions, the global radiative forcing resulting from changes in O₃ can be expressed as a sum of forcings from emission changes in different regions. Tropospheric O₃ is considered in present climate policies only through the inclusion of indirect effect of CH₄ on radiative forcing through its impact on O₃ concentrations. The short-lived O₃ precursors (NO_x, CO, and NMHCs) are not directly included in the Kyoto Protocol or any similar climate mitigation agreement. In this study, we quantify the global radiative forcing resulting from a marginal reduction (10%) in anthropogenic emissions of NO_x alone from nine geographic regions and a combined marginal reduction in NO_x, CO, and NMHCs emissions from three regions. We simulate, using the global chemistry transport model MOZART-2, the change in the distribution of global O₃ resulting from these emission reductions. In addition to the short-term reduction in O₃, these emission reductions also increase CH₄ concentrations (by decreasing OH); this increase in CH₄ in turn counteracts part of the initial reduction in O₃ concentrations. We calculate the global radiative forcing resulting from the regional emission reductions, accounting for changes in both O₃ and CH₄. Our results show that changes in O₃ production and resulting distribution depend strongly on the geographical location of the reduction in precursor emissions. We find that the global O₃ distribution and radiative forcing are most sensitive to changes in precursor emissions from tropical regions and least sensitive to changes from midlatitude and high-latitude regions. Changes in CH₄ and O₃ concentrations resulting from NO_x emission reductions alone produce offsetting changes in radiative forcing, leaving a small positive residual forcing (warming) for all regions. In contrast, for combined reductions of anthropogenic emissions of NO_x, CO, and NMHCs, changes in O₃ and CH₄ concentrations result in a net negative radiative forcing (cooling). Thus we conclude that simultaneous reductions of CO, NMHCs, and NO_x lead to a net reduction in radiative forcing due to resulting changes in tropospheric O₃ and CH₄ while reductions in NO_x emissions alone do not.
O'Neill, B., P. Crutzen, A. Grübler, M. H. Duong, Klaus Keller, C. Kolstad, A. Lange, M. Obersteiner, Michael Oppenheimer, W. Pepper, W. Sanderson, and M. Schlesinger, et al., 2006: Learning and Climate Change. Climate Policy, http://www.geosc.psu.edu/~kkeller/O%27Neill_cp_07.pdf, 6,
[ Abstract ]
Learning � i.e. the acquisition of new information that leads to changes in our assessment of uncertainty � plays a prominent role in the international climate policy debate. For example, the view that we should postpone actions until we know more continues to be influential. The latest work on learning and climate change includes new theoretical models, better informed simulations of how learning affects the optimal timing of emissions reductions, analyses of how new information could affect the prospects for reaching and maintaining political agreements and for adapting to climate change, and explorations of how learning could lead us astray rather than closer to the truth. Despite the diversity of this new work, a clear consensus on a central point is that the prospect of learning does not support the postponement of emissions reductions today.
Onstott, T. C., D. McGown, J. Kessler, B. S. Lollar, K. K. Lehman, and S. M. Clifford, 2006: Martian CH₄: sources, flux and detection. Astrobiology, 6(2), doi:10.1089/ast.2006.6.377 377-395
[ Abstract ]
Recent observations have detected trace amounts of CH₄ heterogeneously distributed in the martian atmosphere, which indicated a subsurface CH₄ flux of �2 X 10⁵ to 2 X 10⁹ cm^-2 s^-1. Four different origins for this CH₄ were considered: (1) volcanogenic; (2) sublimation of hydrate- rich ice; (3) diffusive transport through hydrate-saturated cryosphere; and (4) microbial CH₄ generation above the cryosphere. A diffusive flux model of the martian crust for He, H₂, and CH₄ was developed based upon measurements of deep fracture water samples from South Africa. This model distinguishes between abiogenic and microbial CH₄ sources based upon their isotopic composition, and couples microbial CH₄ production to H₂ generation by H₂O radiolysis. For a He flux of �10⁵ cm^-2 s^-1 this model yields an abiogenic CH₄ flux and a microbial CH₄ flux of �10⁶ and �10⁹ cm^-2 s^-1, respectively. This flux will only reach the martian surface if CH₄ hydrate is saturated in the cryosphere; otherwise it will be captured within the cryosphere. The sublimation of a hydrate-rich cryosphere could generate the observed CH₄ flux, whereas microbial CH₄ production in a hypersaline environment above the hydrate stability zone only seems capable of supplying �10⁵ cm^-2 s^-1 of CH₄. The model predicts that He/H₂/CH₄/C₂H₆ abundances and the C and H isotopic values of CH₄ and the C isotopic composition of C₂H₆ could reveal the different sources. Cavity ring-down spectrometers represent the instrument type that would be most capable of performing the C and H measurements of CH₄ on near future rover missions and pinpointing the cause and source of the CH₄ emissions.
Onstott, T. C., Li-Hung Lin, M. Davidson, B. Mislowack, M. Borcsik, J. Hall, G. Slater, J. Ward, B. S. Lollar, J. Lippmann-Pipke, E. Boice, and L. Pratt, et al., 2006: The origin and age of biogeochemical trends in deep fracture water of the Witwatersrand Basin, South Africa. Geomicrobiology Journal, 12(6), doi:10.1080/01490450600875688 369-414
[ Abstract ]
Water residing within crustal fractures encountered during mining at depths greater than 500 meters in the Witwatersrand basin of South Africa represents a mixture of paleo-meteoric water and 2.0�2.3 Ga hydrothermal fluid. The hydrothermal fluid is highly saline, contains abiogenic CH>sub>4 and hydrocarbon, occasionally N₂, originally formed at ∼250�300°C and during cooling isotopically exchanged O and H with minerals and accrued H₂, ⁴He and other radiogenic gases. The paleo-meteoric water ranges in age from ∼10 Ka to >1.5 Ma, is of low salinity, falls along the global meteoric water line (GMWL) and is CO₂ and atmospheric noble gas-rich. The hydrothermal fluid, which should be completely sterile, has probably been mixing with paleo-meteoric water for at least the past∼100 Myr, a process which inoculates previously sterile environments at depths >2.0 to 2.5 km. Free energy flux calculations suggest that sulfate reduction is the dominant electron acceptor microbial process for the high salinity fracture water and that it is 10⁷ times that normally required for cell maintenance in lab cultures. Flux calculations also indicate that the potential bio available chemical energy increases with salinity, but because the fluence of bioavailable C, N and P also increase with salinity, the environment remains energy-limited. The ⁴He concentrations and theoretical calculations indicate that the H₂ that is sustaining the subsurface microbial communities (e.g. H₂-utilizing SRB and methanogens) is produced by water radiolysis at a rate of ∼1nMyr⁻¹. Microbial CH₄ mixes with abiogenicCH₄ to produce the observed isotopic signatures and indicates that the rate of methanogenesis diminishes with depth from∼100 at < 1 kmbls, to <0.01nMyr⁻¹ at >3 kmbls. Microbial Fe(III) reduction is limited due to the elevated pH. The δ¹³C of dissolved inorganic carbon is consistent with heterotrophy rather than autotrophy dominating the deeper, more saline environments. One potential source of the organic carbon may be microfilms present on the mineral surfaces.
Oppenheimer, Michael, 2006: Science and Environmental Policy: The Role of Nongovernmental Organizations. Social Research, http://findarticles.com/p/articles/mi_m2267/is_3_73/ai_n27052540/,
[ Abstract ]
THIS PAPER ADDRESSES THE ROLE OF NONGOVERNMENTAL ORGANIZATIONS, or NGOs, in the science-policy nexus. I shall draw on my 21 years of experience working for a nongovernmental organization, Environmental Defense, my earlier experience as a research scientist, and my recent experience as a professor, the latter two positions at large universities. I hope this quasi-anecdotal approach is informative, but in addition, it is a necessity because there have been relatively few academic studies of nongovernmental advocacy organizations.
Patra, P. K., K. R. Gurney, A. S. Denning, S. T. Maksyutov, T. Nakazawa, D. Baker, P. Bousquet, L. Bruhwiler, Y.-H. Chen, P. Ciais, S. Fan, I. Y. Fung, and M. N. Gloor, et al., 2006: Sensitivity of inverse estimation of annual mean CO₂ sources and sinks to ocean-only sites versus allsites observational networks. Geophysical Research Letters, 33(L05814), doi:10.1029/2005GL025403
[ Abstract ]
Inverse estimation of carbon dioxide (CO₂) sources and sinks uses atmospheric CO₂ observations, mostly made near the Earth�s surface. However, transport models used in such studies lack perfect representation of atmospheric dynamics and thus often fail to produce unbiased forward simulations. The error is generally larger for observations over the land than those over the remote/marine locations. The range of this error is estimated by using multiple transport models (16 are used here). We have estimated the remaining differences in fluxes due to the use of ocean-only versus all-sites (i.e., over ocean and land) observations of CO₂ in a time-independent inverse modeling framework. The fluxes estimated using the ocean-only networks are more robust compared to those obtained using all-sites networks. This makes the global, hemispheric, and regional flux determination less dependent on the selection of transport model and observation network.
Sarmiento, Jorge, and N. Gruber, 2006: Ocean Biogeochemical Dynamics. Ocean Biogeochemical Dynamics, Princeton University Press, ISBN:13:978-0-691-01,
[ Abstract ]
Ocean Biogeochemical Dynamics provides a broad theoretical framework upon which graduate students and upper-level undergraduates can formulate an understanding of the processes that control the mean concentration and distribution of biologically utilized elements and compounds in the ocean. Though it is written as a textbook, it will also be of interest to more advanced scientists as a wide-ranging synthesis of our present understanding of ocean biogeochemical processes.
The first two chapters of the book provide an introductory overview of biogeochemical and physical oceanography. The next four chapters concentrate on processes at the airsea interface, the production of organic matter in the upper ocean, the remineralization of organic matter in the water column, and the processing of organic matter in the sediments. The focus of these chapters is on analyzing the cycles of organic carbon, oxygen, and nutrients.
The next three chapters round out the authors' coverage of ocean biogeochemical cycles with discussions of silica, dissolved inorganic carbon and alkalinity, and CaCO₃. The final chapter discusses applications of ocean biogeochemistry to our understanding of the role of the ocean carbon cycle in interannual to decadal variability, paleoclimatology, and the anthropogenic carbon budget. The problem sets included at the end of each chapter encourage students to ask critical questions in this exciting new field. While much of the approach is mathematical, the math is at a level that should be accessible to students with a year or two of college level mathematics and/or physics.
Socolow, Robert H., and Stephen W. Pacala, 2006: A Plan to Keep Carbon in Check. Scientific American, http://www.scientificamerican.com/carbon/0906050.pdf, 295(3), 50-57
[ Abstract ]
Humanity can emit only so much carbon dioxide into the atmosphere before the climate enters a state unknown in recent geologic history and goes haywire. Climate scientists typically see the risks growing rapidly as CO₂ levels approach a doubling of their pre-18thcentury value. To make the problem manageable, the required reduction in emissions can be broken down into �wedges��an incremental reduction of a size that matches available technology.
Socolow, Robert H., 2006: Stabilization Wedges: An Elaboration of the Concept. Avoiding Dangerous Climate Change, Schellnhuber, H.J., et al., eds., Cambridge University Press, Cambridge, MA, http://homepage.mac.com/marty.hoffert/filechute/SocolowRedux.pdf, Chapter 36, 347-354
[ Abstract ]
We have earlier introduced the stabilization wedge as a useful unit for discussing climate stabilization. A wedge is 1GtC/yr or emissions savings in 2055, achieved by a single strategy that will not occur without deliberate attention to global carbon. Implementing seven wedges should place humanity, approximately, on a path to stabilizing the climate at a concentration less than double the pre-industrial concentration, leaving those at the helm in the following 50 years in a position to drive CO₂ emissions to net zero emissions; arguably, the tasks of the two half-centuries are comparably difficult. We elaborate on the concept of the stabilization wedge that is achieved through carbon policy by introducing the "virtual" wedge that is achieved as a result of the continued decarbonization of the global economy even in the absence of carbon policy. Virtual wedges are already embedded in almost all "baseline" scenarios, because the decarbonization of the global economy is a robust historical trend. Thus, the stabilization wedges must be achieved over and above the structural shifts, evergy efficiency gains, and energy system decarbonization that are likely to occur in the next 50 years even without carbon policy. We discuss stabilization wedges of energy efficiency, calling attention to the importance of avoiding investments in durable capital facilities, like power plants and apartment buildings, that are energy-inefficient or carbon-wasteful. We briefly explore wedges of capture and storage, nuclear energy, and renewable energy. The wedges framework highlights the importance of early involvement of the developing countries in mitigation activity. The wedges framework, therefore, may be able to contribute new elements to global carbon policy, by aligning the concept of differentiated responsibilities across countries with a global commitment to the internationally coordinated commercialization of low-carbon technology.
Socolow, Robert H., et al., June 2006: Tributes to Amulya Reddy. Energy for Sustainable Development, 10(2), doi:10.1016/S0973-0826(08)60526-8 15
[ Abstract ]
With Amulya Reddy�s passing we have lost a dear friend and colleague. In our collaboration that came to be known as �The Gang of Four� and spanned nearly three decades, we learned much from each other that we were able to transform into a global strategy to put energy on a track that promotes sustainable development. Amulya will continue to live on in our hearts and minds as a result of this collectively evolved strategy that would be very incomplete without Amulya�s imprint. Though others know much more about the impacts of his activities at the local, state, and national levels in India, we would like to share with colleagues a history of our collaboration that highlights Amulya�s legacy at the international level.
Succar, Samir, J. B. Greenblatt, D. C. Denkenberger, and Robert H. Williams, 2006: An Integrated Optimization Of Large-Scale Wind With Variable Rating Coupled To Compressed Air Energy Storage. Proceedings of the AWEA Windpower 2006, Pittsburgh, PA, http://www.princeton.edu/~ssuccar/recent/Succar_AWEAPaper_June06.pdf,
[ Abstract ]
A methodology is presented for jointly optimizing the wind turbine specific rating and the storage configuration for a large-scale wind farm coupled to compressed air energy storage (CAES). By allowing the wind-storage system to be optimized in an integrated, variable rating framework the overall cost of energy (COE) can be reduced substantially. These changes also enhance the capacity factor of the wind array, reduce the storage capacity requirements of the baseload plant and reduce the greenhouse gas emission rate of the overall system relative to a separately optimized wind farm couple to CAES. The results of this analysis could have important implications for th ecompetitiveness of large-scale remote wind and the applicability of energy storage as a baseload wind strategy in a carbon constrained world.
Tiwari, Y. K., M. N. Gloor, R. J. Engelen, F. Chevallier, C. Rödenbeck, S. Korner, P. Peylin, B. H. Brasswell, and M. Heimann, 2006: Comparing CO₂ retrieved from Atmospheric Infrared Sounder with model predictions: implications for constraining surface fluxes and lower�to-upper troposphere transport. Journal of Geophysical Research, 111(D17106), doi:10.1029/2005JD006681
[ Abstract ]
Large-scale carbon sources and sinks can be estimated by combining atmospheric CO₂ concentration data with atmospheric transport inverse modeling. This approach has been limited by sparse spatiotemporal tropospheric sampling. CO₂ estimates from space using observations on recently launched satellites (Atmospheric Infrared Sounder (AIRS)), or platforms to be launched (Infrared Atmospheric Sounding Interferometer (IASI), Orbiting Carbon Observatory (OCO)) have the potential to fill some of these gaps. Here we assess the realism of initial AIRS-based mid-to-upper troposphere CO₂ estimates from European Centre for Medium-Range Weather Forecasts by comparing them with simulations of two transport models (TM3 and Laboratoire Meteorologie Dynamique Zoom (LMDZ)) forced with one data-based set of surface fluxes. The simulations agree closer with one another than with the retrievals. Nevertheless, there is good overall agreement between all estimates of seasonal cycles and north-south gradients within the latitudinal band extending from 30°S to 30°N, but not outside this region. At smaller spatial scales, there is a contrast in the satellite-based retrievals above continents versus above oceans that is absent in the model predictions. Hovmoeller diagrams indicate that in the models, high Northern Hemisphere winter CO₂ concentrations propagate toward the tropical upper troposphere via Northern Hemisphere high latitudes, while in retrievals, elevated winter CO₂ appears instantaneously throughout the Northern Hemisphere. This raises questions about lower-to-upper troposphere transport pathways. Prerequisites for use of retrievals to provide an improved constraint on surface fluxes are therefore further improvements in retrievals and better understanding/validation of lower-to-upper troposphere transport and its modeling. This calls for more independent upper troposphere transport tracer data like SF₆ and CO₂.
Tol, R.S.J., Robert H. Socolow, and Stephen W. Pacala, 2006: Understanding Long-Term Energy Use and Carbon Dioxide Emissions in the USA. Fondazione Eni Enrico Mattei Working Papers, doi:10.1016/j.jpolmod.2008.12.002
[ Abstract ]
We compile a database of energy uses, energy sources, and carbon dioxide emissions for the USA for the period 1850-2002. We use a model to extrapolate the missing observations on energy use by sector. Overall emission intensity rose between 1850 and 1917, and fell between 1917 and 2002. The leading cause for the rise in emission intensity was the switch from wood to coal, but population growth, economic growth, and electrification contributed as well. After 1917, population growth, economic growth and electrification pushed emissions up further, and there was no net shift from fossil to non-fossil energy sources. From 1850 to 2002, emissions were reduced by technological and behavioural change (particularly in transport, manufacturing and households), structural change in the economy, and a shift from coal to oil and gas. These trends are stronger than electrification, explaining the fall in emissions relative to GDP.
Balaji, V., J. Anderson, I. Held, M. Winton, J. Durachta, S. Malyshev, and R. J. Stouffer, May 2005: The Exchange Grid: a mechanism for data exchange between Earth System components on independent grids. Parallel Computational Fluid Dynamics 2005 - Theory and Applications, Elsevier, http://www.gfdl.noaa.gov/~vb/pdf/xgridpaper.pdf, 179-188
[ Abstract ]
We present a mechanism for exchange of quantities between components of a coupled Earth system model, where each component is independently discretized. The exchange grid is formed by overlaying two grids, such that each exchange grid cell has a unique parent cell on each of its antecedent grids. In Earth System models in particular, processes occurring near component surfaces require special surface boundary layer physical processes to be represented on the exchange grid. The exchange grid is thus more than just a stage in a sequence of regridding between component grids. We present the design and use of a 2-dimensional exchange grid on a horizontal planetary surface in the GFDL Flexible Modeling System (FMS), highlighting issues of parallelism and performance.
Bender, Michael, D. T. Ho, M. B. Hendricks, R. Mika, M. Battle, P. P. Tans, T. J. Conway, B. Sturtevant, and N. Cassar, 2005: Atmospheric O₂/N₂ changes, 1993�2002: Implications for the partitioning of fossil fuel CO₂ sequestration. Global Biogeochemical Cycles, 19(GB4017), doi:10.1029/2004GB002410
[ Abstract ]
Improvements made to an established mass spectrometric method for measuring changes in atmospheric O₂/N₂ are described. With the improvements in sample handling and analysis, sample throughput and analytical precision have both increased. Aliquots from duplicate flasks are repeatedly measured over a period of 2 weeks, with an overall standard error in each flask of 3�4 per meg, corresponding to 0.6�0.8 ppm O₂ in air. Records of changes in O₂/N₂ from six global sampling stations (Barrow, American Samoa, Cape Grim, Amsterdam Island, Macquarie Island, and Syowa Station) are presented. Combined with measurements of CO₂ from the same sample flasks, land and ocean carbon uptake were calculated from the three sampling stations with the longest records (Barrow, Samoa, and Cape Grim). From 1994�2002, We find the average CO₂ uptake by the ocean and the land biosphere was 1.7 � 0.5 and 1.0 � 0.6 GtC yr^-1 respectively; these numbers include a correction of 0.3 Gt C yr^-1 due to secular outgassing of ocean O₂. Interannual variability calculated from these data shows a strong land carbon source associated with the 1997�1998 El Nin�o event, supporting many previous studies indicating that high atmospheric growth rates observed during most El Ninõ events reflect diminished land uptake. Calculations of interannual variability in land and ocean uptake are probably confounded by non-zero annual air sea fluxes of O₂. The origin of these fluxes is not yet understood.
Bohlman, S. A., and D. Lashlee, 2005: High spatial and spectral resolution remote sensing of Panama Canal Zone watershed forests: An applied example mapping tropical tree species. The Rio Chagres: A Multidisciplinary Profile of a Tropical Watershed, 52, doi:10.1007/1-4020-3297-8_16 245-258
[ Abstract ]
High spatial resolution airborne and satellite sensors have been used with varying degrees of success to measure deciduousness, canopy structure, and light interception, and to identify tree species in the Panama Canal Watershed. Results reported to date indicate that remotely sensed data have a high degree of accuracy in measuring deciduousness and leaf density in the upper canopy, but less accuracy than in temperate systems in measuring canopy light interception for semi-deciduous lowland tropical forests in the canal watershed. Of particular relevance to evergreen forests like the upper R�o Chagres basin, this work examines whether high spectral resolution data, like that collected by the HYDICE system, can separate canopy species based on hyperspectral signatures in the 0.4 to 2.5-μm wavelength region. If a few well-selected spectral bands could accurately differentiate species, tropical canopies in remote and rugged terrain could be mapped using relatively simple, but optimized sensor systems.
Donner, S. D., W. J. Skirving, C. M. Little, Michael Oppenheimer, and O. Hoegh-Guldberg, 2005: Global assessment of coral bleaching and required rates of adaptation under climate change. Global Change Biology, 11(12), doi:10.1111/j.1365-2486.2005.01073.x 2251-2265
[ Abstract ]
Elevated ocean temperatures can cause coral bleaching, the loss of colour from reefbuilding corals because of a breakdown of the symbiosis with the dinoflagellate Symbiodinium. Recent studies have warned that global climate change could increase the frequency of coral bleaching and threaten the long-term viability of coral reefs. These assertions are based on projecting the coarse output from atmosphere�ocean general circulation models (GCMs) to the local conditions around representative coral reefs. Here, we conduct the first comprehensive global assessment of coral bleaching under climate change by adapting the NOAA Coral ReefWatch bleaching prediction method to the output of a low- and high-climate sensitivity GCM. First, we develop and test algorithms for predicting mass coral bleaching with GCM-resolution sea surface temperatures for thousands of coral reefs, using a global coral reef map and 1985�2002 bleaching prediction data. We then use the algorithms to determine the frequency of coral bleaching and required thermal adaptation by corals and their endosymbionts under two different emissions scenarios. The results indicate that bleaching could become an annual or biannual event for the vast majority of the world�s coral reefs in the next 30�50 years without an increase in thermal tolerance of 0.2 � 1.0°C per decade. The geographic variability in required thermal adaptation found in each model and emissions scenario suggests that coral reefs in some regions, like Micronesia and western Polynesia, may be particularly vulnerable to climate change. Advances in modelling and monitoring will refine the forecast for individual reefs, but this assessment concludes that the global prognosis is unlikely to change without an accelerated effort to stabilize atmospheric greenhouse gas concentrations.
Dunne, J. P., R. A. Armstrong, A. Gnanadesikan, and Jorge Sarmiento, 2005: Empirical and mechanistic models for the particle export ratio. Global Biogeochemical Cycles, 19(GB40226), doi:10.1029/2004GB002390
[ Abstract ]
We present new empirical and mechanistic models for predicting the export of organic carbon out of the surface ocean by sinking particles. To calibrate these models, we have compiled a synthesis of field observations related to ecosystem size structure, primary production and particle export from around the globe. The empirical model captures 61% of the observed variance in the ratio of particle export to primary production (the pe ratio) using sea-surface temperature and chlorophyll concentrations (or primary productivity) as predictor variables. To describe the mechanisms responsible for pe-ratio variability, we present size-based formulations of phytoplankton grazing and sinking particle export, combining them into an alternative, mechanistic model. The formulation of grazing dynamics, using simple power laws as closure terms for small and large phytoplankton, reproduces 74% of the observed variability in phytoplankton community composition wherein large phytoplankton augment small ones as production increases. The formulation for sinking particle export partitions a temperature-dependent fraction of small and large phytoplankton grazing into sinking detritus. The mechanistic model also captures 61% of the observed variance in pe ratio, with large phytoplankton in high biomass and relatively cold regions leading to more efficient export. In this model, variability in primary productivity results in a biomass-modulated switch between small and large phytoplankton pathways.
Edmonds, J., F. Joos, N. Nakicenovic, R. G. Richels, and Jorge Sarmiento, 2005: Scenarios, targets, gaps, and costs. The Global Carbon Cycle, Washington, D.C., Island Press, http://www.climate.unibe.ch/~joos/OUTGOING/publications/edmonds03scope_finalproofs_11-30-03.pd, 62, 77-102
[ Abstract ]
This paper explores the connection between human activities and the concentration of carbon dioxide in the atmosphere. It explores the implication of the wide range of emissions scenarios developed by the IPCC in the Special Report on Emissions Scenarios and concludes that a robust finding is that major changes will be required in the global energy system if the concentration of carbon dioxide is eventually to be stabilized.
Fiore, A. M., L. W. Horowitz, D. W. Purves, H. Levy II, M. J. Evans, Y. Wang, Y. Li, and R. M. Yantosca, 2005: Evaluating the contribution of changes in isoprene emissions to surface ozone trends over the eastern United States. Journal of Geophysical Research, 110(D12303), doi:10.1029/2004JD005485
[ Abstract ]
Reducing surface ozone (O₃) to concentrations in compliance with the national air quality standard has proven to be challenging, despite tighter controls on O₃ precursor emissions over the past few decades. New evidence indicates that isoprene emissions changed considerably from the mid-1980s to the mid-1990s owing to land-use changes in the eastern United States (Purves et al., 2004). Over this period, U.S. anthropogenic VOC (AVOC) emissions decreased substantially. Here we apply two chemical transport models (GEOS-CHEM and MOZART-2) to test the hypothesis, put forth by Purves et al. (2004), that the absence of decreasing O₃ trends over much of the eastern United States may reflect a balance between increases in isoprene emissions and decreases in AVOC emissions. We find little evidence for this hypothesis; over most of the domain, mean July afternoon (1300�1700 local time) surface O₃ is more responsive (ranging from -9 to +7 ppbv) to the reported changes in anthropogenic NO_x emissions than to the concurrent isoprene (-2 to +2 ppbv) or AVOC (-2 to 0 ppbv) emission changes. The estimated magnitude of the O₃ response to anthropogenic NO_x emission changes, however, depends on the base isoprene emission inventory used in the model. The combined effect of the reported changes in eastern U.S. anthropogenic plus biogenic emissions is insufficient to explain observed changes in mean July afternoon surface O₃ concentrations, suggesting a possible role for decadal changes in meteorology, hemispheric background O₃, or subgrid-scale chemistry. We demonstrate that two major uncertainties, the base isoprene emission inventory and the fate of isoprene nitrates (which influence surface O₃ in the model by -15 to +4 and +4 to +12 ppbv, respectively), preclude a well-constrained quantification of the present-day contribution of biogenic or anthropogenic emissions to surface O₃ concentrations, particularly in the high-isopreneemitting southeastern United States. Better constraints on isoprene emissions and chemistry are needed to quantitatively address the role of isoprene in eastern U.S. air quality.
Gruner, Sol M., Pierre A. Piroue, and Robert H. Socolow, October 2005: George T. Reynolds (an obituary). Physics Today, http://www.physicstoday.org,
Hastings, M. G., Daniel Sigman, and E. J. Steig, 2005: Glacial/interglacial changes in the isotopes of nitrate from the Greenland Ice Sheet Project 2 (GISP2) ice core. Global Biogeochemical Cycles, 7, doi:10.1029/2005GB002502 611-625
[ Abstract ]
The ¹⁵N/¹⁴N and ¹⁸O/¹⁶O ratios of nitrate in the Greenland Ice Sheet Project 2 (GISP2) (Summit, Greenland) ice core are much higher in ice from the last glacial period than in the pre-industrial Holocene, despite the lack of a significant glacial/interglacial change in nitrate concentration. While both the ¹⁵N/¹⁴N and ¹⁸O/¹⁶O records are anticorrelated with snow accumulation rate, neither is satisfactorily explained by accumulation changes or post-depositional processes. The similarity in the glacial/ interglacial change in ¹⁵N/¹⁴N from several different Greenland ice cores and the large amplitude of this change relative to observed seasonal variation raise the possibility that the isotopes of nitrate in ice cores indicate a large-scale glacial/interglacial change in the isotopic composition of atmospheric NO_x. The glacial/interglacial change in ¹⁸O/¹⁶O is best explained by a greater contribution of HNO₃ production from hydrolysis of N₂O₅, which has implications for reconstruction of past atmospheric oxidant levels. Although isotope effects associated with NO_x photochemistry and nitrate scavenging have not been fully characterized, the ¹⁵N/¹⁴N data may indicate glacial/interglacial changes in the relative contributions from different natural sources of NO_x on a hemispheric or global scale.
Haug, G. H., A. Ganopolski, Daniel Sigman, A. Rosell-Mele, G.E.A. Swann, R. Tiedemann, S. L. Jaccard, J. Bollman, R. J. Matear, M. J. Leng, and G. Eglinton, 2005: North Pacific seasonality and the glaciation of North America 2.7 million years ago. Nature, 433, doi:10.1038/nature03332 821-825
[ Abstract ]
In the context of gradual Cenozoic cooling, the timing of the onset of significant Northern Hemisphere glaciation 2.7 million years ago is consistent with Milankovitch�s orbital theory, which posited that ice sheets grow when polar summertime insolation and temperature are low. However, the role of moisture supply in the initiation of large Northern Hemisphere ice sheets has remained unclear. The subarctic Pacific Ocean represents a significant source of water vapour to boreal North America, but it has been largely overlooked in efforts to explain Northern Hemisphere glaciation. Here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic Pacific Ocean, indicating that 2.7 million years ago latesummer sea surface temperatures in this ocean region rose in response to an increase in stratification. At the same time, winter sea surface temperatures cooled, winter floating ice became more abundant and global climate descended into glacial conditions. We suggest that the observed summer warming extended into the autumn, providing water vapour to northern North America, where it precipitated and accumulated as snow, and thus allowed the initiation of Northern Hemisphere glaciation.
Jaccard, S. L., G. H. Haug, Daniel Sigman, T. F. Pedersen, H. R. Thierstein, and U. Röhl, 2005: Glacial/interglacial changes in subarctic North Pacific stratification. Science, 308, doi:10.1126/science.1108696 1003-1006
[ Abstract ]
Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.
Kaiser, J., M. K. Reuer, B. Barnett, and Michael Bender, 2005: Marine productivity estimates from continuous oxygen/argon ratio measurements by membrane inlet mass spectrometry. Geophysical Research Letters, 32(L19605), doi:10.1029/2005GL023459
[ Abstract ]
Dissolved oxygen/argon (O₂/Ar) ratios in the oceanic mixed layer are indicative of net community production (NCP) because O₂ and Ar share similar physical solubility properties, but only O₂ is biologically produced and consumed. We describe a membrane inlet mass spectrometer (MIMS) that allows continuous high-precision shipboard analysis of O₂/Ar ratios and eventually other gases, calibrated with discrete samples analyzed in the laboratory. We also present O₂/Ar data from the eastern equatorial Pacific. Shortterm reproducibilities of 0.05% were achieved. Meridional gradients and small-scale phenomena were clearly resolved. O₂/Ar undersaturations around the equator reflect the interaction of biological and physical forcings. Mixed-layer NCP estimated from wind speed-gas exchange parameterizations was near zero north of 2.75�N, and about 12 mmol m^-2 d^-1 south of 6.75�S. Ar supersaturations, calculated from MIMS O₂/Ar measurements and accompanying O₂ concentration measurements, ranged from -0.8 to +3.0%.
Keller, Klaus, M. G. Hall, S.-R. Kim, David F. Bradford, and Michael Oppenheimer, 2005: Avoiding dangerous anthropogenic interference with the climate system. Climatic Change, 73(3), doi:10.1007/s10584-005-0426-8 227-238
[ Abstract ]
The UN Framework Convention on Climate Change calls for the avoidance of �dangerous anthropogenic interference with the climate system�. Among the many plausible choices, dangerous interference with the climate system may be interpreted as anthropogenic radiative forcing causing distinct and widespread climate change impacts such as a widespread demise of coral reefs or a disintegration of the West Antarctic ice sheet. The geological record and numerical models suggest that limiting global warming below critical temperature thresholds significantly reduces the likelihood of these eventualities. Here we analyze economically optimal policies that may ensure this risk-reduction. Reducing the risk of a widespread coral reef demise implies drastic reductions in greenhouse gas emissions within decades. Virtually unchecked greenhouse gas emissions to date (combined with the inertia of the coupled natural and human systems) may have already committed future societies to a widespread demise of coral reefs. Policies to reduce the risk of a West Antarctic ice sheet disintegration allow for a smoother decarbonization of the economy within a century and may well increase consumption in the long run.
Kieft, T. L., S. M. McCuddy, T. C. Onstott, M. Davidson, Li-Hung Lin, B. Mislowack, L. Pratt, E. Boice, B. S. Lollar, J. Lippmann-Pipke, S. M. Pfiffner, and T. J. Phelps, et al., 2005: Geochemically Generated, Energy-Rich Substrates and Indigenous Microorganisms in Deep, Ancient Groundwater. Geomicrobiology Journal, 22(6), doi:10.1080/01490450500184876 325-355
[ Abstract ]
Recent studies have shown that the biosphere extends to depths that exceed 3 km, raising questions regarding the age of the microbes in these deep ecosystems and their sources of energy for metabolism. Abiogenic energy sources that are derived from in situ, purely geochemical sources and thus independent from photosynthesis have been suggested.We sampled saline fracture water emanating from a 3.1-km deep borehole in a Au mine in the Witwatersrand Basin of South Africa and characterized the chemical constituents (including stable isotopes), groundwater age, and indigenous microorganisms. Salinity data and ratios of dissolved noble gases indicate that extremely ancient (2.0 Ga) saline fracture water has mixed with meteoric water to yield an average subsurface residence time of 20�160 Ma, the oldest age of any waters collected to date in the Witwatersrand Basin. H₂ isotope data suggest the water originated from a depth of 4 to 5 km. Sulfur isotope fractionation indicates biological sulfate reduction. Calculations of free energies and steady state energy fluxes based on water chemistry data also support sulfate reduction as the dominant terminal electron accepting process. Lipid and flow cytometry data indicate a sparse microbial community (103 cells ml⁻¹), despite the presence of relatively high concentrations of energy-rich compounds (H₂, CH₄, CO, ethane, propane, butane, and acetate). The H₂ can be explained by radiolysis of water. Stable isotopic signatures of the CH₄ and short chain hydrocarbons indicate abiogenic synthesis. The persistence of energy-rich compounds suggests that other factors are limiting to microbial metabolism and growth, e.g., availability of an inorganic nutrient, such as Fe or phosphate.
Livnat, A., Stephen W. Pacala, and S. A. Levin, 2005: The Evolution of Intergenerational Discounting in Offspring Quality. American Naturalist, http://www.journals.uchicago.edu/doi/pdf/10.1086/428294?cookieSet=1, 165(3), 311-321
[ Abstract ]
Intergenerational effects occur when an individual�s actions affect not only its own survivorship and reproduction but also those of its offspring and possibly later descendants. In the presence of intergenerational effects, short-term and long-term measures of success (such as the expected numbers of surviving offspring and of farther descendants, respectively) may be in conflict. When such conflicts occur, life-history theory normally takes long-termmeasures to predict the outcome of selection. This ignores the fact that, because traits change in time�through mutation, sex, and recombination� long-term relations disintegrate. We study this issue with numerical simulations and analytical models combining intergenerational effects and evolutionary change. In the models, the parental investment per offspring, as well as the total reproductive effort, stand for investments in future generations. The models show that the rate of evolutionary change determines the level of those investments. Higher rates of mutation and of sexual as opposed to parthenogenetic reproduction favor lower parental investment per offspring and lower total reproductive effort. It follows that the level of investment of ancestors in descendants responds to the genetic relatedness between the generations of the lineage, in a manner unaccounted for by preexisting theory.
Oppenheimer, Michael, and A. Petsonk, 2005: Article 2 of the UNFCCC: Historical Origins, Recent Interpretations. Climatic Change, 73(3), doi:10.1007/s10584-005-0434-8 195-226
[ Abstract ]
Article 2 of the UN Framework Convention on Climate Change (UNFCCC), which states the treaty�s long-term objective, is the subject of a growing literature that examines means to interpret and implement this provision. Here we provide context for these studies by exploring the intertwined scientific, legal, economic, and political history of Article 2. We review proposed definitions for �dangerous anthropogenic interference� and frameworks that have been proposed for implementing these definitions. Specific examples of dangerous climate changes suggest limits on global warming ranging from 1 to 4°C and on concentrations ranging from 450 to 700 ppm CO₂ equivalents. The implications of Article 2 for near term restrictions on greenhouse-gas emissions, e.g., the Kyoto Protocol, are also discussed.
Oppenheimer, Michael, and R. B. Alley, 2005: Ice Sheets, Global Warming, and Article 2 of the UNFCCC. Climatic Change, 68(3), doi:10.1007/s10584-005-5372-y 257-267
[ Abstract ]
Rapid disintegration of the West Antarctic ice sheet (WAIS) was cited decades ago as a potentially severe consequence of global warming (Mercer, 1968, 1978; Revelle, 1983) and climate scientists have cast a wary eye toward the cryosphere ever since. Total loss of the West Antarctic or Greenland ice sheet (GIS) would cause eustatic sea level rise of 4�6 m and 7 m, respectively. The stability of the much larger East Antarctic ice sheet (EAIS) is sometimes questioned but it is likely that the two other ice sheets would disintegrate with less warming. Initially, WAIS was the main focus of concern because as a marine ice sheet, it was thought by many to be inherently unstable (Oppenheimer, 1998). That WAIS has undergone a large reduction in area and perhaps in mass since the Last Glacial Maximum (Bindschadler, 1998; Huybrechts, 2002) provides evidence of its vulnerability to global temperature and sea level variations. In contrast, GIS is estimated to have shrunken by about 30% from its LGM volume (Fleming and Lambeck, 2004). Disintegration ofWAIS may provide a plausible example of �dangerous anthropogenic interference with the climate system� under Article 2 of theUNFramework Convention on Climate Change. In this context, two recent studies proposed specific temperatures and greenhouse gas concentrations (O�Neill and Oppenheimer, 2002, Oppenheimer and Alley, 2004) to be avoided. A key issue is the degree to which warming can affect the rate of ice loss by altering the mass balance between precipitation rates on the one hand, and melting and ice discharge to the ocean through ice streams on the other.
Oppenheimer, Michael, 2005: Defining Dangerous Anthropogenic Interference: The Role of Science, the Limits of Science. Workshop Perspectives on Dangerous Climate Change, Tyndall Centre, Norwich, UK, 25(6), doi:10.1111/j.1539-6924.2005.00687.x 1399-1407
[ Abstract ]
Defining "dangerous anthropogenic interference" with the climate system in the context of Article 2 of the UN Framework Convention on Climate Change (UNFCCC) presents a complex challenge for those developing long-term climate policy. Natural science has a key role to play in quantifying vulnerabilities of elements of the Earth system and estimating the risks from a changing climate. But attempts to interpret Article 2 will inevitably draw on understanding from social science, psychology, law, and ethics. Here I consider the limits of science in defining climate "danger" by focusing on the potential disintegration of the major ice sheets as an example of an extreme impact. I show that considerations of timescale, uncertainty, and learning preclude a definition of danger drawn purely from natural science. Decision makers will be particularly challenged by one characteristic of global problems: answers to some scientific questions become less accurate over decadal timescales, meandering toward the wrong answer, a feature I call negative learning. I argue for a precautionary approach to Article 2 that would be based initially on current, limited scientific understanding of the future of the ice sheets.
Orr, J. C., V. J. Fabry, O. Aumont, L. Bopp, S. C. Doney, R. A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R. M. Key, and K. Lindsay, et al., 2005: Anthropogenic ocean acidification over the 21st century and its impact on marine calcifying organisms. Nature, 437, doi:10.1038/nature04095 681-686
[ Abstract ]
Today�s surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms�such as corals and some plankton�will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean�carbon cycle to assess calcium carbonate saturation under the IS92a �business-as-usual� scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.
Purves, D. W., and Stephen W. Pacala, 2005: Ecological drift in niche-structured communities: neutral pattern does not imply neutral process. Biotic Interactions in the Tropics, Chapter 5, 107-138
[ Abstract ]
We can define a neutral community as one in which all species, and so all individuals, are equivalent, in the sense that they are interchangeable at all times and under all conditions. In contrast, we can define a structured community as one in which species are not equivalent, and species-specified differences affect the population dynamics, and therefore the behaviour of the community. This distinction is an important one, because in a neutral community the biodiversity, as measured by species richness and abundance patterns, has nothing to do with the biogeochemical functioning of the community (e.g. carbon fixation and nutrient-cycling). In fact, in a truly neutral community one could eliminate all but one species without affecting the biogeochemical functioning of the community at all. In contrast, much of the species-specific variation in biological traits observed in reality has direct relevance for the functioning of the community. For example, the short-term carbon uptake of a forest depends on the growth rates of the individual trees, and the long-term carbon storage depends on adult life-span and wood density, and there is wide species-specific variation in these traits. In niche-structured communities, the biodiversity and functioning are intimately linked, and some combination of at least some species is required to maintain the functioning of the community. In the most highly structured community possible there is no equivalence between any of the species, which is the so-called �one species one niche� idea so prevalent in the history of ecology: in such a community, removing just one species has a significant impact on the dynamics and functioning of the community. Which of these two pictures of communities � neutral or structured � is nearer to the truth? Is it �one species one niche� or �all species one niche�? This is the neutral vs structure debate, and it continues apace because there is good evidence for both sides of the argument.
Purves, D. W., and J. Dushoff, 2005: Directed seed dispersal and metapopulation response to habitat loss and disturbance: application to Eichhornia paniculata. Journal of Ecology, 93(4), doi:10.1111/j.1365-2745.2005.00988.x 658-669
[ Abstract ]
1. Seed dispersal is often directed towards locations with particular characteristics, particularly where seeds are dispersed by animals. The potential importance of directed seed dispersal for the response of plant metapopulations to habitat loss and changes in disturbance rate is assessed, and illustrated with a case study of a metapopulation of an aquatic plant. 2. The Levins model is extended to include preferential dispersal towards suitable habitat and towards unoccupied patches. Both increase patch occupancy, decrease the minimum habitat cover required for persistence and increase the maximum allowable disturbance rate, while preferential dispersal towards unoccupied patches also makes reductions in abundance due to increased disturbance rates more threshold-like. 3. Applying classical metapopulation approaches, which assume random dispersal, to a species that features directed dispersal, is expected to give systematic errors in prediction. For example, where dispersal is directed towards suitable habitat regardless of occupancy, the Levins model will tend to overestimate the response to habitat loss, and where dispersal is directed towards unoccupied patches, the Levins model will tend to underestimate the response to changes in disturbance rate. 4. Eichhornia paniculata is an aquatic plant restricted to ephemeral pools. Seed dispersal is by waterfowl, and so is directed towards suitable habitat. Data on habitat cover and patch occupancy from Husband and Barrett in 1998 fit well with our model but deviate significantly from the predictions of the Levins model. The parameter estimates imply dispersal very strongly directed towards suitable habitat, and that without this the minimum density of pools required for persistence would be at least 10 times greater than the highest densities observed, implying that the species would go locally extinct. 5. To our knowledge, this is the first quantitative demonstration that the nature and strength of directed dispersal affects the robustness of fragmented plant populations to anthropogenic disturbance. This calls for increased attention to be paid to the behaviour of seed-dispersing animals, and how this behaviour varies between different plant communities.
Robinson, R. S., Daniel Sigman, P. J. DiFiore, M. M. Rohde, T. A. Mashiotta, and D. W. Lea, 2005: Diatombound ¹⁵N/¹⁴N: New support for enhanced nutrient consumption in the ice age Subantarctic. Paleoceanography, 20(PA303), doi:10.1029/2004PA001114
[ Abstract ]
Diatom-bound ¹⁵N/¹⁴N was used to reconstruct the glacial nutrient status of the Subantarctic Zone in the Southern Ocean. Down-core records from both the Pacific and Indian sectors show δ¹⁵N of 5 to 6% during the Last Glacial Maximum and a decrease, coincident with the glacial termination, to values as low as 2%. The effect of either diatom assemblage or physiological change on the diatom-bound ¹⁵N/¹⁴N is unknown and cannot yet be ruled out as a possible explanation for the observed change. However, the consistency between Indian and Pacific sector records and with other paleoceanographic data suggests that the glacial-interglacial difference in diatom-bound ¹⁵N/¹⁴N was driven by higher consumption of nitrate in the subantarctic surface during the last ice age. Such a change in nutrient consumption may have resulted from atmospheric iron fertilization and/or decreased glacial mixed layer depths associated with sea ice melting. Enhanced nutrient consumption in the glacial subantarctic would have worked to lower the concentration of CO₂ in the ice age atmosphere. It also would have reduced the preformed nutrient content of the low-latitude thermocline, leading to decreases in lowlatitude productivity, suboxia, and denitrification.
Sandin, S. A., and Stephen W. Pacala, 2005: Demographic theory of coral reef fish populations with stochastic recruitment: comparing sources of population regulation. American Naturalist, 165(1), doi:10.1086/426674 107-119
[ Abstract ]
The effects of three forms of density-dependent regulation were explored in model coral reef fish populations: top-down (predation), bottom-up (competition for food), and pelagic (non-reefbased mechanisms) control. We describe the demographic responses of both biomass and numbers of adult fish, predicting the mean and the variance of temporal fluctuations resulting from stochastic recruitment of juveniles. We find that top-down control acts by suppressing variability of numbers of fish, which in turn suppresses the variability of biomass. Bottom-up control has no effect on fluctuations of numbers of fish, though it strongly reduces fluctuations of biomass. Because fecundity of fish is directly linked to body mass, the regulation of biomass tightly regulates reproductive output independently of the number of individuals in the population. Finally, populations under pelagic control experience bounded fluctuations of biomass and numbers directly proportional to the bounded fluctuations of recruitment. The demographic signatures predicted from both bottom-up and pelagic control are consistent with current evidence supporting the recruitment limitation hypothesis in reef fish ecology. We propose tests to discriminate the dominant mode of density-dependent regulation using qualitative trends in time series demographic data across environmental clines.
Sandin, S. A., and Stephen W. Pacala, 2005: Fish aggregation results in inversely density dependent predation on continuous coral reefs. Ecology, 86(6), doi:10.1890/03-0654 1520-1530
[ Abstract ]
Spatially density-dependent predation is a leading hypothesis describing mechanisms of population regulation in coral reef fish. However, studies supporting this hypothesis predominantly have been conducted on small, isolated patch reefs. Here, we searched for evidence of spatially density-dependent predation on the continuous reefs of the Netherlands Antilles in a study of a dominant planktivore, the blue chromis (Chromis cyanea). Across space, we quantified both the patterns of loss from site-attached aggregations of C. cyanea through time and the behavioral reaction of predators to these aggregations. Looking across C. cyanea densities, we found that loss from aggregations was not characteristic of direct density dependence, but instead was commonly inversely related to density. Individual C. cyanea in larger aggregations were less likely to be lost from the group than were individuals in smaller aggregations. Thus, the observed density dependence increased spatial heterogeneity of C. cyanea. Predators showed behaviors that were consistent with these demographic patterns. Using remote videography, we quantified predator visitation and strike rates across a range of C. cyanea aggregation sizes. Predators consistently visited and struck at individuals in C. cyanea aggregations in a pattern that was strongly inversely density dependent, suggesting that aggregation is an effective means of minimizing per capita risk of predation for prey reef fish. Differences in spatial distribution of resources for predators (i.e., prey fish) between continuous and patch reef habitats may explain the difference between these results and those of previous studies on patch reefs.
Sigman, Daniel, J. Granger, P. J. DiFiore, K. K. Lehman, R. Ho, G. Cane, and A. van Geen, 2005: Coupled nitrogen and oxygen isotope measurements of nitrate along the eastern North Pacific margin. Global Biogeochemical Cycles, 19(GB4022), doi:10.1029/2005GB002458
[ Abstract ]
Water column depth profiles along the North Pacific margin from Point Conception to the tip of Baja California indicate elevation of nitrate (NO₃) ¹⁵N/¹⁴N and ¹⁸O/¹⁶O associated with denitrification in the oxygen-deficient thermocline waters of the eastern tropical North Pacific. The increase in δ¹⁸O is up to 3% greater than in δ¹⁵N, whereas our experiments with denitrifier cultures in seawater medium indicate a 1:1 increase in NO₃ δ¹⁸O and δ¹⁵N during NO₃ consumption. Moreover, the maximum in NO₃ δ¹⁸O is somewhat shallower than the maximum in NO₃ δ¹⁵N. These two observations can be summarized as an ��anomaly�� from the 1:1 δ¹⁸O-to-δ¹⁵N relationship expected from culture results. Comparison among stations and with other data indicates that this anomaly is generated locally. The anomaly has two plausible interpretations: (1) the addition of low-δ¹⁵N NO₃ to the shallow thermocline by the remineralization of newly fixed nitrogen, or (2) active cycling between NO₃ and NO₂ (coupled NO₃ reduction and NO₂ oxidation) in the suboxic zone.
Socolow, Robert H., 2005: Can We Bury Global Warming? Scientific American, http://www.princeton.edu/mae/people/faculty/socolow/socdoc/buryglobalwarming.pdf, 293(1), 49-55
[ Abstract ]
When William Shakespeare took a breath, 280 molecules out of every million entering his lungs were carbon dioxide. Each time you draw breath today, 380 molecules per million are carbon dioxide. That portion climbs about two molecules every year. No one knows the exact consequences of this upsurge in the atmosphere�s carbon dioxide (CO₂) concentration nor the effects that lie ahead as more and more of the gas enters the air in the coming decades - humankind is running an uncontrolled experiment on the world. Scientists know that carbon dioxide is warming the atmosphere, which in turn is causing sea level to rise, and that the CO₂ absorbed by the oceans is acidifying the water. But they are unsure of exactly how climate could alter across the globe, how fast sea level might rise, what a more acidic ocean could mean, which ecological systems on land and in the sea would be most vulnerable to climate change and how these developments might affect human health and well-being. Our current course is bringing climate change upon ourselves faster than we can learn how severe the changes will be.
Tohjima, Y., H. Mukai, T. Machida, Y. Nojiri, and M. N. Gloor, 2005: First measurements of the latitudinal atmospheric O₂ and CO₂ distributions across the Western Pacific. Geophysical Research Letters, 32(L17805), doi:10.1029/2005GL023311
[ Abstract ]
We examine the latitudinal distribution of the tracer ��atmospheric potential oxygen�� APO = O₂ + 1.1 X CO₂ between 40�S and 50�N using new atmospheric CO₂ and O₂ measurements from flask samples collected onboard cargo ships between Japan and the United States, and Japan and Australia (or New Zealand) during the period from December 2001 to August 2004. Because APO is unaltered during photosynthesis and respiration by land vegetation, its atmospheric distribution is tightly linked to the air-sea gas exchange of O₂ and CO₂ and the underlying processes. We find that the seasonal amplitude of APO increases towards high latitudes in both hemispheres and its minimum is located approximately 10-degree north of the equator. The latitudinal distribution of annual mean APO shows a maximum in the tropics, confirming the recent coupled ocean-atmosphere model predictions for this region.
Baidya Roy, S., Stephen W. Pacala, and R. L. Walko, 2004: Can large wind farms affect local meteorology? Journal of Geophysical Research, 109(D19101), doi:10.1029/2004JD004763
[ Abstract ]
The RAMS model was used to explore the possible impacts of a large wind farm in the Great Plains region on the local meteorology over synoptic timescales under typical summertime conditions. A wind turbine was approximated as a sink of energy and source of turbulence. The wind farm was created by assuming an array of such turbines. Results show that the wind farm significantly slows down the wind at the turbine hub-height level. Additionally, turbulence generated by rotors create eddies that can enhance vertical mixing of momentum, heat, and scalars, usually leading to a warming and drying of the surface air and reduced surface sensible heat flux. This effect is most intense in the early morning hours when the boundary layer is stably stratified and the hub-height level wind speed is the strongest due to the nocturnal low-level jet. The impact on evapotranspiration is small.
Deutsch, C., Daniel Sigman, R. C. Thunell, A. N. Meckler, and G. H. Haug, 2004: Isotopic constraints on glacial/interglacial changes in the oceanic nitrogen budget. Global Biogeochemical Cycles, 18(GB4012), doi:10.1029/2003GB002189
[ Abstract ]
We investigate the response of the ¹⁵N/¹⁴N of oceanic nitrate to glacial/interglacial changes in the N budget, using a geochemical box model of the oceanic N cycle that includes N₂ fixation and denitrification in the sediments and suboxic water column. This model allows us to quantify the isotopic response of different oceanic nitrate pools to deglacial increases in water column and sedimentary denitrification, given a range of possible feedbacks between nitrate concentration and N₂ fixation/denitrification. This response is compared to the available paleoceanographic data, which suggest an early deglacial maximum in nitrate ¹⁵N/¹⁴N in suboxic zones and no significant glacialto- late Holocene change in global ocean nitrate ¹⁵N/¹⁴N. Consistent with the work of Brandes and Devol [2002], we find that the steady state ¹⁵N/¹⁴N of oceanic nitrate is controlled primarily by the fraction of total denitrification that occurs in the water column. Therefore a deglacial peak in the ratio of water column-to-sediment denitrification, caused by either a strong feedback between water column denitrification and the N reservoir or by an increase in sediment denitrification due to sea level rise, can explain the observed deglacial ¹⁵N/¹⁴N maximum in sediments underlying water column denitrification zones. The total denitrification rate and the mean ocean nitrate concentration are also important determinants of steady state nitrate ¹⁵N/¹⁴N. For this reason, modeling a realistic deglacial ¹⁵N/¹⁴N maximum further requires that the combined negative feedbacks from N₂ fixation and denitrification are relatively strong, and N losses are relatively small. Our results suggest that the glacial oceanic N inventory was at most 30% greater than today�s and probably less than 10% greater.
Doney, S. C., K. Lindsay, K. Caldeira, J.-M. Campin, H. Drange, J. C. Dutay, M. Follows, Y. Gao, A. Gnanadesikan, N. Gruber, A. Ishida, and F. Joos, et al., 2004: Evaluating global ocean carbon models: The importance of realistic physics. Global Biogeochemical Cycles, 18(GB3017), doi:10.1029/2003GB002150
[ Abstract ]
A suite of standard ocean hydrographic and circulation metrics are applied to the equilibrium physical solutions from 13 global carbon models participating in phase 2 of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2). Model-data comparisons are presented for sea surface temperature and salinity, seasonal mixed layer depth, meridional heat and freshwater transport, 3-D hydrographic fields, and meridional overturning. Considerable variation exists among the OCMIP-2 simulations, with some of the solutions falling noticeably outside available observational constraints. For some cases, model-model and model-data differences can be related to variations in surface forcing, subgrid-scale parameterizations, and model architecture. These errors in the physical metrics point to significant problems in the underlying model representations of ocean transport and dynamics, problems that directly affect the OCMIP predicted ocean tracer and carbon cycle variables (e.g., air-sea CO₂ flux, chlorofluorocarbon and anthropogenic CO₂ uptake, and export production). A substantial fraction of the large model-model ranges in OCMIP-2 biogeochemical fields (�25�40%) represents the propagation of known errors in model physics. Therefore the model-model spread likely overstates the uncertainty in our current understanding of the ocean carbon system, particularly for transport-dominated fields such as the historical uptake of anthropogenic CO₂. A full error assessment, however, would need to account for additional sources of uncertainty such as more complex biological-chemical-physical interactions, biases arising from poorly resolved or neglected physical processes, and climate change.
Doney, S. C., C. J. Kucharik, and Michael Oppenheimer, 2004: The Influence of Climate on In-stream Removal of Nitrogen. Geophysical Research Letters, 31(L20509), doi:10.1029/2004GL020477
[ Abstract ]
Nitrogen (N) removal via benthic denitrification in large river systems can be a significant sink of terrestrial N and a source of nitrous oxide (N₂O) to the atmosphere. Recent studies have demonstrated the fraction of in-stream N removed from a river reach is related to the water residence time. We used the HYDRA aquatic transport model to examine the sensitivity of in-stream N removal and the associated N₂O emissions in the Mississippi River system to the interannual variability in climate. The results suggested an almost two-fold range in the percent of N removed in the Mississippi River system and a three-fold range in the associated N₂O emissions, with the lowest percent removed (10�33%) and the highest N₂O emissions (15.5�26.0 106 kg N) occurring in the wettest years. The results demonstrate the importance of considering climate variability and change in the management of nutrient export by large rivers.
Dutay, J. C., P. Jean-Baptiste, J.-M. Campin, A. Ishida, E. Maier-Reimer, R. J. Matear, A. Mouchet, I. J. Totterdell, Y. Yamanaka, K. B. Rodgers, G. Madec, and J. C. Orr, 2004: Evaluation of OCMIP-2 Ocean Models� Deep Circulation with Mantle Helium-3. Journal of Marine Systems, 48(1-4), doi:10.1016/j.jmarsys.2003.05.010 15-36
[ Abstract ]
We compare simulations of the injection of mantle helium-3 into the deep ocean from six global coarse resolution models which participated in the Ocean Carbon Model Intercomparison Project (OCMIP). We also discuss the results of a study carried out with one of the models, which examines the effect of the subgrid-scale mixing parameterization. These sensitivity tests provide useful information to interpret the differences among the OCMIP models and between model simulations and the data. We find that the OCMIP models, which parameterize subgrid-scale mixing using an eddy-induced velocity, tend to underestimate the ventilation of the deep ocean, based on diagnostics with δ³He. In these models, this parameterization is implemented with a constant thickness diffusivity coefficient. In future simulations, we recommend using such a parameterization with spatially and temporally varying coefficients in order to moderate its effect on stratification. The performance of the models with regard to the formation of AABW confirms the conclusion from a previous evaluation with CFC-11. Models coupled with a sea-ice model produce a substantial bottom water formation in the Southern Ocean that tends to overestimate AABW ventilation, while models that are not coupled with a sea-ice model systematically underestimate the formation of AABW. We also analyze specific features of the deep ³He distribution (³He plumes) that are particularly well depicted in the data and which put severe constraints on the deep circulation. We show that all the models fail to reproduce a correct propagation of these plumes in the deep ocean. The resolution of the models may be too coarse to reproduce the strong and narrow currents in the deep ocean, and the models do not incorporate the geothermal heating that may also contribute to the generation of these currents. We also use the context of OCMIP-2 to explore the potential of mantle helium-3 as a tool to compare and evaluate modeled deep-ocean circulations. Although the source function of mantle helium is known with a rather large uncertainty, we find that the parameterization used for the injection of mantle helium-3 is sufficient to generate realistic results, even in the Atlantic Ocean where a previous pioneering study [J. Geophys. Res. 100 (1995) 3829] claimed this parameterization generates inadequate results. These results are supported by a multi-tracer evaluation performed by considering the simulated distributions of both helium-3 and natural ¹⁴C, and comparing the simulated tracer fields with available data.
Gnanadesikan, A., J. P. Dunne, I. Aavatsmark, R. M. Key, Jorge Sarmiento, R. D. Slater, and P. S. Swathi, 2004: Oceanic ventilation and biogeochemical cycling: Understanding the physical mechanisms that produce realistic distributions of tracers and productivity. Global Biogeochemical Cycles, 18(GB4010), doi:10.1029/2003GB002097
[ Abstract ]
Differing models of the ocean circulation support different rates of ventilation, which in turn produce different distributions of radiocarbon, oxygen, and export production. We examine these fields within a suite of general circulation models run to examine the sensitivity of the circulation to the parameterization of subgridscale mixing and surface forcing. We find that different models can explain relatively high fractions of the spatial variance in some fields such as radiocarbon, and that newer estimates of the rate of biological cycling are in better agreement with the models than previously published estimates. We consider how different models achieve such agreement and show that they can accomplish this in different ways. For example, models with high vertical diffusion move young surface waters into the Southern Ocean, while models with high winds move more young North Atlantic water into this region. The dependence on parameter values is not simple. Changes in the vertical diffusion coefficient, for example, can produce major changes in advective fluxes. In the coarse-resolution models studied here, lateral diffusion plays a major role in the tracer budget of the deep ocean, a somewhat worrisome fact as it is poorly constrained both observationally and theoretically.
Greenblatt, J. B., and Jorge Sarmiento, 2004: Variability and climate feedback mechanisms in ocean uptake of CO₂. The Global Carbon Cycle, 62, Chapter 13, 257-278
[ Abstract ]
The major sinks of anthropogenic CO₂ are the oceans and terrestrial biosphere, which absorbed half the 6.3 ± 0.4 petagrams of carbon per year (PgC v^-1) emitted by fossil-fuel burning in the 1990s (Prentice et al. 2001). Because of the enormous size of these sinks, it is important to understand not only their mean size, but also their variation. Interannual variability appears to be significant for both the ocean and terrestrial sinks, though different methods currently yield conflicting results. In addition, global climate change resulting from emission of CO₂ can induce changes in the sizes of the ocean and terrestrial sinks. Those changes may have already begun, as evidenced by ocean temperature increases (Levitus et al. 2000), and changes in ocean carbon uptake (Prentice et al. 2001). Based on deep oceanic chlorofluorocarbon (CFC) and radiocarbon (&delta¹⁴C) measurements, Broecker et al (1999) suggest that ocean circulation may have changed in the past century, and time-series measurements of atmospheric and oceanic CO₂ concentrations point to changes already taking place in the ocean's buffering chemistry (Sarmiento et al. 1995). This chapter focuses on anthropogenic changes to the ocean carbon cycle, while Le Quéré and Metzl (Chapter 12) discuss natural processes regulating ocean CO₂ uptake, and Foley and Ramankutty (Chapter 14) treat the terrestrial carbon cycle. We begin with the current understanding of uptake variability, then explore the effects of climate change on the rates of CO₂ uptake, including long-term changes in uptake due to changing ocean chemistry. We also consider the potential effects of large-scale changes in ocean circulation, such as a collapse of the thermohaline circulation in the North Atlantic Ocean. We end with a discussion of future research needs.
Gummer MP, The Rt Hon John, C. Butler, E. Claussen, H. Cavalcanti, D. Dillon-Ridgley, D. Gyawali, S. Kato, L. Li, J. Marton-Lefèvre, S. Rayner, T. Smyth, Robert H. Socolow, Sir C. Tickell, and N. Witoszek FitzPatrick, April 2004: Oxford Commission on Sustainable Consumption Report In , Oxford, Mansfield College,
[ Abstract ]
The Commission was established in 1999 by the Oxford Centre for the Environment, Ethics and Society (OCEES), then a research institute of Mansfield College in the University of Oxford.
The report is the product of discussion among members of the Commission in the period 2000-2002, supported by studies by the staff of OCEES, the deliberations of a number of expert workshops and meetings, research projects in Brazil and Nepal, and studies in China, Japan and a number of other countries.
The subject of sustainable consumption was chosen because, although a question obviously important in itself, it has been given comparatively little attention either by international policymakers or by academics. This is despite the fact that it was considered of real relevance in the conclusions of the Rio Conference of 1992 and highlighted in the work of the Johannesburg Conference ten years later. Although there has been some significant work under the auspices of the United Nations Environment Programme and the Organisation for Economic Co-operation and Development, sustainable consumption needs a good deal of further work if satisfactory policies are to be developed.
Hastings, M. G., E. J. Steig, and Daniel Sigman, 2004: Seasonal variations in N and O isotopes of nitrate in snow at Summit, Greenland: Implications for the study of nitrate in snow and ice cores. Journal of Geophysical Research � Atmosphere, 109(D20306), doi:10.1029/2004JD004991
[ Abstract ]
Nitrogen and oxygen isotopes of NO₃ have been measured in snow and firn from Summit, Greenland. The ¹⁵N/¹⁴N and ¹⁸O/¹⁶O ratios of NO₃ in recently fallen snow are similar to those of surface snow. Diurnal variation is observed in ¹⁵N/¹⁴N of NO₃, and possibly ¹⁸O/¹⁶O, suggesting fractionating loss of NO₃ from snow during the day, which is subsequently recovered at night. A larger seasonal variation is observed, with higher ¹⁵N/¹⁴N and lower ¹⁸O/¹⁶O of NO₃ in summer than winter, which cannot be explained by postdepositional fractionation. The generally high ¹⁸O/¹⁶O of NO₃ in Greenland snow (δ¹⁸O versus VSMOW = 65.2 to 79.6%) indicates that oxygen atoms from ozone have been incorporated into NO_x that was subsequently deposited as HNO₃. The lower mean δ¹⁸O of NO₃ in summer snow relative to winter (68.9% in summer 2000 and 70.5% in summer 2001 versus 77.5% in winter 2000�01) is a result of summertime HNO₃ production via NO₂ reaction with hydroxyl radical (OH), which dilutes the high δ¹⁸O imparted on NO₂ from ozone. The higher mean ¹⁵N/¹⁴N of NO₃ observed in snow from spring (δ¹⁸O versus air N₂ = +5.9% in 2000 and -1.4% in 2001) and summer (+0.1% in 2000 and -0.8% in 2001) than fall (-9.2% in 2000) and winter( -10.0% in 2000�01) is more difficult to explain with seasonal photochemistry, given current knowledge. The seasonal ¹⁵N/¹⁴N change may reflect NO_X sources, with a greater fall and wintertime contribution from fossil fuel emissions relative to other inputs of NO_X (i.e., biogenic soil emissions, biomass burning, and lightning).
Hurtt, G. C., R. Dubayah, J. Drake, P. R. Moorcroft, Stephen W. Pacala, J. B. Blair, and M. G. Fearon, 2004: Beyond Potential Vegetation: Combining Lidar Data and a Height Structured Model for Carbon Studies. Ecological Applications, 14(3), doi:10.1890/02-5317 873-883
[ Abstract ]
Carbon estimates from terrestrial ecosystem models are limited by large uncertainties in the current state of the land surface. Natural and anthropogenic disturbances have important and lasting influences on ecosystem structure and fluxes that can be difficult to detect or assess with conventional methods. In this study, we combined two recent advances in remote sensing and ecosystem modeling to improve model carbon stock and flux estimates at a tropical forest study site at La Selva, Costa Rica (10�25' N, 84�00' W). Airborne lidar remote sensing was used to measure spatial heterogeneity in the vertical structure of vegetation. The ecosystem demography model (ED) was used to estimate the consequences of this heterogeneity for regional estimates of carbon stocks and fluxes. Lidar data provided substantial constraints on model estimates of both carbon stocks and net carbon fluxes. Lidar-initialized ED estimates of aboveground biomass were within 1.2% of regression-based approaches, and corresponding model estimates of net carbon fluxes differed substantially from bracketing alternatives. The results of this study provide a promising illustration of the power of combining lidar data on vegetation height with a heightstructured ecosystem model. Extending these analyses to larger scales will require the development of regional and global lidar data sets, and the continued development and application of height structured ecosystem models.
Keith, D. W., J. F. De Carolis, D. C. Denkenberger, D. H. Lenschow, S. Malyshev, Stephen W. Pacala, and P. J. Rasch, 2004: The Influence of Large-scale Wind-power on Global Climate. Proceedings of the National Academy of Sciences of the United States of America, 101(46), doi:10.1073/pnas.0406930101 16115-16120
[ Abstract ]
Large-scale use of wind power can alter local and global climate by extracting kinetic energy and altering turbulent transport in the atmospheric boundary layer. We report climate-model simulations that address the possible climatic impacts of wind power at regional to global scales by using two general circulation models and several parameterizations of the interaction of wind turbines with the boundary layer. We find that very large amounts of wind power can produce nonnegligible climatic change at continental scales. Although large-scale effects are observed, wind power has a negligible effect on global-mean surface temperature, and it would deliver enormous global benefits by reducing emissions of CO₂ and air pollutants. Our results may enable a comparison between the climate impacts due to wind power and the reduction in climatic impacts achieved by the substitution of wind for fossil fuels.
Marinov, I., and Jorge Sarmiento, 2004: The role of the oceans in the global carbon cycle: An overview. The Ocean Carbon Cycle and Climate, Ankara, Turkey, Kluwer Academic Publishers, 251-295
[ Abstract ]
Typical gases such as oxygen tend to be distributed mostly in the atmosphere (99.4%) and less so in the ocean (0.6%). Carbon dioxide is vastly different from such gases, with 98.5% of the pre-industrial CO₂ in the ocean and only 1.5% in the atmosphere. The reason that CO₂ is found preferentially in the ocean is because of its high solubility (thirty times that of oxygen) and because of the hydrolysis reaction it undergoes to form carbonate and bicarbonate ions. The oceanic carbon inventory of total dissolved inorganic carbon (DIC ) is also influenced by a combination of biologically mediated processes (the biological pump) and physical and chemical processes (the solubility pump). Both the biological and solubility pumps contribute to a higher concentration of DIC in the deep ocean, which reduces atmospheric CO₂ relative to what it would be otherwise. The fact that the largest part of the total carbon inventory is in the ocean suggests that the ocean exerts a dominant control on atmospheric CO₂. Section 1 introduces the carbon pumps and their role in modulating pCO_2atm on the glacial-interglacial time scale. Human activities such as fossil fuel burning, production of cement, and land use change (e.g., tropical deforestation, land conversion for crops) have led to an increase in emissions of carbon dioxide, three quarters of which is due to fossil fuel burning. As a consequence, the partial pressure of carbon dioxide in the atmosphere has increased from 280± 10 ppm before the industrial revolution to 373 ppm in 2002, the highest CO₂ level recorded in the past 20 million years. This spectacular increase is similar to the change that occurred in going from glacial to interglacial periods. However, the present increase has happened within less than 200 years, while glacial-interglacial variations occurred on a time scale of thousands of years.
Matsumoto, K., Jorge Sarmiento, R. M. Key, O. Aumont, J. L. Bullister, K. Caldeira, J.-M. Campin, S. C. Doney, H. Drange, J. C. Dutay, Y. Gao, A. Gnanadesikan, and N. Gruber, et al., 2004: Evaluation of ocean carbon cycle models with data-based metrics. Geophysical Research Letters, 31(L07303), doi:10.1029/2003GL018970
[ Abstract ]
New radiocarbon and chlorofluorocarbon-11 data from the World Ocean Circulation Experiment are used to assess a suite of 19 ocean carbon cycle models. We use the distributions and inventories of these tracers as quantitative metrics of model skill and find that only about a quarter of the suite is consistent with the new databased metrics. This should serve as a warning bell to the larger community that not all is well with current generation of ocean carbon cycle models. At the same time, this highlights the danger in simply using the available models to represent the state-of-the-art modeling without considering the credibility of each model.
Mignone, B. K., Jorge Sarmiento, R. D. Slater, and A. Gnanadesikan, 2004: Sensitivity of sequestration efficiency to mixing processes in the global ocean. Energy, 29(9-10), doi:10.1016/j.energy.2004.03.080 1467-1478
[ Abstract ]
A number of large-scale sequestration strategies have been considered to help mitigate rising levels of atmospheric carbon dioxide (CO₂). Here, we use an ocean general circulation model (OGCM) to evaluate the efficiency of one such strategy currently receiving much attention, the direct injection of liquid CO₂ into selected regions of the abyssal ocean. We find that currents typically transport the injected plumes quite far before they are able to return to the surface and release CO₂ through air�sea gas exchange. When injected at sufficient depth (well within or below the main thermocline), most of the injected CO₂ outgasses in high latitudes (mainly in the Southern Ocean) where vertical exchange is most favored. Virtually all OGCMs that have performed similar simulations confirm these global patterns, but regional differences are significant, leading efficiency estimates to vary widely among models even when identical protocols are followed. In this paper, we make a first attempt at reconciling some of these differences by performing a sensitivity analysis in one OGCM, the Princeton Modular Ocean Model. Using techniques we have developed to maintain both the modeled density structure and the absolute magnitude of the overturning circulation while varying important mixing parameters, we estimate the sensitivity of sequestration efficiency to the magnitude of vertical exchange within the low-latitude pycnocline. Combining these model results with available tracer data permits us to narrow the range of model behavior, which in turn places important constraints on sequestration efficiency.
O'Neill, B., and Michael Oppenheimer, 2004: Climate Change Impacts Sensitive to Path to Stabilization. Proceedings of the National Academy of Sciences of the United States of America, 101, doi:10.1073/pnas.0405522101 16411-16416
[ Abstract ]
Analysis of policies to achieve the long-term objective of the United Nations Framework Convention on Climate Change, stabilizing concentrations of greenhouse gases at levels that avoid ��dangerous�� climate changes, must discriminate among the infinite number of emission and concentration trajectories that yield the same final concentration. Considerable attention has been devoted to path-dependent mitigation costs, generally for CO₂ alone, but not to the differential climate change impacts implied by alternative trajectories. Here, we derive pathways leading to stabilization of equivalent CO₂ concentration (including radiative forcing effects of all significant trace gases and aerosols) with a range of transient behavior before stabilization, including temporary overshoot of the final value. We compare resulting climate changes to the sensitivity of representative geophysical and ecological systems. Based on the limited available information, some physical and ecological systems appear to be quite sensitive to the details of the approach to stabilization. The likelihood of occurrence of impacts that might be considered dangerous increases under trajectories that delay emissions reduction or overshoot the final concentration.
Oppenheimer, Michael, and R. B. Alley, 2004: The West Antarctic Ice Sheet and Long Term Climate Policy. Climatic Change, 64(1-2), doi:10.1023/B:CLIM.0000024792.06802.31 1-10
[ Abstract ]
Disintegration of the West Antarctic ice sheet (WAIS) has long served as a benchmark of dangerous climate change (Mercer, 1968, 1978; Revelle, 1983; Smith et al., 2001). Recent findings with implications for the future of the West Antarctic ice sheet in a warming world (Rott et al., 2002; De Angelis and Skvarca, 2003) may be of importance to policy makers and others (Berk et al., 2002) grappling with the meaning of Article 2 of the U.N. Framework Convention on Climate Change and its injunction to avoid �dangerous anthropogenic interference with the climate system.� These observations show acceleration of glaciers coupled to abrupt ice-shelf disintegration along the Antarctic Peninsula (Doake et al., 1998). The key issue is whether the main body of the ice sheet would behave similarly if its ice shelves were thinned or removed by a warming climate. The accompanying editorial essay by Dessai et al. (2004) argues �internal definitions of dangerous climate change ��danger as experienced� � warrants at least as much attention as external definitions � �danger as defined� �. We agree that the interpretation of Article 2 ought to expand beyond traditional approaches grounded in climatology, biology, economics and engineering. The editorial further states �it is not possible to make progress on defining dangerous climate change, or in developing sustainable responses to this global problem, without recognising the central role played by social or individual perceptions of danger.� There is a substantial risk in adopting the latter view. Addressing the psychological and much of the social dimension of dangerous climate change is in its infancy in comparison to the decades-old process of physical assessment. An equally prolonged discussion of the social and psychological dimension is in the offing. The continuing increase in greenhouse gas concentrations could make certain dangers unavoidable unless a preliminary interpretation of Article 2, based largely on the �external� framework, is implemented (O�Neill and Oppenheimer, 2002). In practice, such an approach already may be feasible for a handful of climate changes, such as the �large-scale discontinuities� (e.g. disintegration of WAIS, shutdown of the thermohaline circulation) noted in the Third Assessment Report of the Intergovernmental Panel on Climate Change (Smith et al., 2001). The recent glaciological findings provide an opportunity to consider how a long-term objective consistent with Article 2 might be selected, because they shed new light on the range of climate change that may trigger disintegration of WAIS. Here we explore the key scientific issues and consider a long-term approach to limiting greenhouse gas concentrations based upon these observations, tied to the viability of the major West Antarctic ice shelves.We believe the consequences of a WAIS collapse would be so large that despite uncertainties, external considerations supplemented by a precautionary interpretation of the recent observations may be sufficient to define dangerous levels of climate change, and the corresponding greenhouse gas (ghg) concentrations.
Oppenheimer, Michael, 2004: Book Review: The Discovery of Global Warming. Journal of Environmental History, 9, 327-328
[ Abstract ]
As a scientific problem, global warming has a history dating back at least to Fourier in 1827. Its origins as a political issue are much more recent, with serious discussions of limiting greenhouse gas emissions beginning among scientists and economists only in the middle of the 1970s when the prospect of warming vied on an equal footing with the possibility of future cooling of the planet. Policy makers came to the table a decade later. The evolution of the climate question from science to politics and back and forth has been the subject of surprisingly few in-depth treatments. This void leads to a damaging lack of perspective in the public debate. Without the context of history, assertions like "not long ago, the same scientists who now warn us of warming were alarmists over global cooling" or "global warming is a left wing plot hatched by anti-capitalist environmentalists" too often go unchallenged. Spencer Weart's The Discovery of Global Warming goes a long way toward rectifying this situation. Weart, director of the Center for the History of Physics at the American Institute of Physics, is most effective at laying out the early scientific developments, and discussing how scientists moved the issue onto governmental research agendas. He is somewhat less effective in describing political developments once the issue veered squarely into the policy arena. Weart highlights the importance of the actions of networks of scientists in constructing a bridge from science to policy on an arcane issue of no apparent urgency to the general public. He correctly points to the key leadership role of Swedish climatologist Bert Bolin in shepherding his colleagues toward consensus, beginning in the late 1960s. Weart's exploration of the science-policy interaction in the 1970s, which focused largely on increasing support for research, is thorough. His discussion of scientists' activity after the mid-1980s, which helped build the road to the U.N. Framework Convention on Climate Change and the Kyoto Protocol, is more superficial. One of the most useful features of this book is the timeline of events following the last chapter. Oddly, it ends at 1988 because "the period since 1988 is too recent to identify historical milestones." Perhaps this is a valid assertion from a historian's professional viewpoint. But the importance of some events, like the signing of the Framework Convention in 1992, is likely to endure. In contrast, the author is quite willing to highlight scientific questions, like the potential importance of warming-induced shifts in the major ocean circulation, whose significance also may not become clear for decades. But never mind these shortcomings. The clear value of this book to scholars, reporters, and the interested public will hopefully spawn additional efforts that will fill these gaps, and lead to a greater understanding of scientists as political actors. The Discovery of Global Warming has done us all a great favor by pointing the way.
Oppenheimer, Michael, September 2004: Reinvigorating the Kyoto System and Beyond: Maintaining the Fundamental Architecture, Meeting Long-Term Goals. Leaders� Summit on Post-Kyoto Architecture: Toward an L20, http://www.princeton.edu/step/people/faculty/michael-oppenheimer/recent-publications/,
[ Abstract ]
While it is increasingly clear that anthropogenic emissions of greenhouse gases (GHGs) are causing potentially irreversible shifts in Earth's climate, efforts to craft a durable and effective architecture for addressing the problem remain stymied by deep divisions between north and south, between major emitting nations and those that will be most affected by global warming, between some nations that are heavily export-dependent on fossil fuels and the rest of the world. Even within governments, disagreements among different ministries with different mandates have stalled action. This delay is not without cost: every year that nations postpone action to reverse GHG emissions growth and bring forward a robust response, the time window for averting dangerous levels of climate change narrows. The L20 provides a potentially important forum that could offer much needed global leadership on innovative approaches for overcoming international divisions on this crucial challenge. In particular, L20 leaders' experience in strengthening the world's international financial architecture provides an important lens through which to view new approaches for the international market-based architecture to reduce GHG emissions. The following paper proposes, for L20 consideration, three approaches to rejuvenating the United Nations Framework Convention on Climate Change (UNFCCC) and its Kyoto process. We ground our argument in these integrated assumptions: The incentive-based architecture that was incorporated, if imperfectly, in the Kyoto Protocol provides an optimal basis to broaden participation and develop a viable long term approach to address climate change. Further, we assert that the Kyoto formulation of successive near-term (decade-scale) targets for limiting total emissions of greenhouse gases (GHGs) provides a necessary element for achieving the long-term goal of the UNFCCC (stated in its Article 2). Our analysis is motivated by three main objectives: 1) US participation, 2) developing country/non-Annex I participation,1 and 3) coupling near-term obligations of the Parties to an effective long-term strategy for limiting climate change.
Pacala, Stephen W., and J. P. Caspersen, et al., 2004: Forest Inventory Data Falsify Ecosystem Models of CO₂ Fertilization. ,
[ Abstract ]
We analyze tree growth data from Wisconsin forest inventories completed in 1968, 1983, 1996 and 2002. These show that the rate of forest growth decreased steadily over the period, in contrast to the increases predicted by CO₂ fertilization models. Measured growth rate changed an average of -0.27% y^-1 (95% confidence range: -0.05% to -0.49% y^-1), whereas the prediction for CO₂ fertilization is 0.16% y^-1 (corresponding to a � of 0.36). The high statistical precision is due both to large sample sizes and positive correlations among the growth rates from different time periods within the same plot. Decreased growth occurred in stands of all ages, and so our results are not caused by age-related declines in growth (although highly significant age-related declines were also detected).
Data allowing a direct examination of growth rates over several decades are available only for Wisconsin, but Caspersen et al. (2000) introduced an indirect method for detecting past changes in growth rate using only two sequential inventories. This method was criticized by Joos et al. (2002), who claimed that it lacked the statistical power to falsify state-of�the-art ecosystem models of CO₂ fertilization. We explain both the sound points and the critical errors in Joos et al.�s argument, introduce a transparent and analytically tractable version of Caspersen et al.�s method, and check its ability to detect the decreasing growth rates in the Wisconsin data. The results show that the indirect method accurately characterizes the past changes that actually occurred, and has sufficient statistical power to falsify CO₂ fertilization models, including the model in Joos et al. (2002).
We discuss the implications of decreasing Wisconsin growth rates, together with other reasons for skepticism about the future magnitude of CO₂ fertilization. In particular, the steep reductions in fossil fuel emissions required to stabilize atmospheric CO₂ at 500 ppm must begin more than a decade sooner if the predictions of the CO₂ fertilization models in the IPCC Third Assessment (Prentice et al. 2001) are incorrect. The difference between a terrestrial carbon sink that grows because of CO₂ fertilization, and one that shrinks because it is caused by recovery from past land use, is the difference between the luxury of a substantial delay and the need to act now.
Pacala, Stephen W., and Robert H. Socolow, 2004: Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies. Science, 305, doi:10.1126/science.1100103 968-972
[ Abstract ]
Humanity already possesses the fundamental scientific, technical, and industrial know-how to solve the carbon and climate problem for the next half-century. A portfolio of technologies now exists to meet the world�s energy needs over the next 50years and limit atmospheric CO₂ to a trajectory that avoids a doubling of the preindustrial concentration. Every element in this portfolio has passed beyond the laboratory bench and demonstration project; many are already implemented somewhere at full industrial scale. Although no element is a credible candidate for doing the entire job (or even half the job) by itself, the portfolio as a whole is large enough that not every element has to be used. The debate in the current literature about stabilizing atmospheric CO₂ at less than a doubling of the preindustrial concentration has led to needless confusion about current options for mitigation. On one side, the Intergovernmental Panel on Climate Change (IPCC) has claimed that �technologies that exist in operation or pilot stage today� are sufficient to follow a less-thandoubling trajectory �over the next hundred years or more� [(1), p. 8]. On the other side, a recent review in Science asserts that the IPCC claim demonstrates �misperceptions of technological readiness� and calls for �revolutionary changes� in mitigation technology, such as fusion, space-based solar electricity, and artificial photosynthesis (2). We agree that fundamental research is vital to develop the revolutionary mitigation strategies needed in the second half of this century and beyond. But it is important not to become beguiled by the possibility of revolutionary technology. Humanity can solve the carbon and climate problem in the first half of this century simply by scaling up what we already know how to do. 13
Purves, D. W., J. P. Caspersen, P. R. Moorcroft, G. C. Hurtt, and Stephen W. Pacala, 2004: Human-induced Changes in U.S. Biogenic Volatile Organic Compound Emissions: evidence from long-term forest inventory data. Global Change Biology, 10(10), doi:10.1111/j.1365-2486.2004.00844.x 1737-1755
[ Abstract ]
Volatile organic compounds (VOCs) emitted by woody vegetation influence global climate forcing and the formation of tropospheric ozone. We use data from over 250 000 re-surveyed forest plots in the eastern US to estimate emission rates for the two most important biogenic VOCs (isoprene and monoterpenes) in the 1980s and 1990s, and then compare these estimates to give a decadal change in emission rate. Over much of the region, particularly the southeast, we estimate that there were large changes in biogenic VOC emissions: half of the grid cells (1° X 1°) had decadal changes in emission rate outside the range -2.3% to +16.8% for isoprene, and outside the range 0.2�17.1% for monoterpenes. For an average grid cell the estimated decadal change in heatwave biogenic VOC emissions (usually an increase) was three times greater than the decadal change in heatwave anthropogenic VOC emissions (usually a decrease, caused by legislation). Leaf-area increases in forests, caused by anthropogenic disturbance, were the most important process increasing biogenic VOC emissions. However, in the southeast, which had the largest estimated changes, there were substantial effects of ecological succession (which decreased monoterpene emissions and had location-specific effects on isoprene emissions), harvesting (which decreased monoterpene emissions and increased isoprene emissions) and plantation management (which increased isoprene emissions, and decreased monoterpene emissions in some states but increased monoterpene emissions in others). In any given region, changes in a very few tree species caused most of the changes in emissions: the rapid changes in the southeast were caused almost entirely by increases in sweetgum (Liquidambar styraciflua) and a few pine species. Therefore, in these regions, a more detailed ecological understanding of just a few species could greatly improve our understanding of the relationship between natural ecological processes, forest management, and biogenic VOC emissions.
Robinson, R. S., B. G. Brunelle, and Daniel Sigman, 2004: Revisiting nutrient utilization in the glacial Antarctic: Evidence from a new method for diatom-bound N isotopic analysis. Paleoceanography, 19(PA3001), doi:10.1029/2003PA000996
[ Abstract ]
Isotopic measurements of diatom-bound nitrogen, using a wet chemical oxidation combined with the ��denitrifier�� method for nitrate analysis, show significant offsets from previously published combustion-based measurements. This offset is attributed to a gaseous nitrogen blank associated with the diatom�s opal frustule. Moreover, experimentation with multiple chemical cleaning protocols demonstrates that diatom microfossils from the clay-rich sediments of the glacial Antarctic are more difficult to clean than Holocene materials. New downcore profiles from the Antarctic show no change in the diatom-bound N ¹⁵N/¹⁴N between the last glacial and the Holocene in the Atlantic sector, and the elevation of glacial diatom-bound ¹⁵N/¹⁴N relative to the Holocene in the Indian sector is smaller than in previous measurements. These data suggest no change in the degree of nitrate utilization in the Atlantic sector and at most a 20% increase (from ~ 25 to 45%) in the Indian sector. The new measurements suggest that, during the last ice age in the Atlantic sector of the Antarctic, the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below. Given the apparent spatial variability in the degree of nitrate drawdown, more work is required to develop an adequate picture of the glacial Antarctic nutrient field.
Rodgers, K. B., O. Aumont, G. Madec, and C. Menkes, 2004: Radiocarbon as a thermocline proxy in th eastern equatorial Pacific. Geophysical Research Letters, 31(L14314), doi:10.1029/2004GL019764
[ Abstract ]
An ocean model is used to test the idea that sea surface Δ¹⁴C behaves as a thermocline proxy in the eastern equatorial Pacific. The ORCA2 model, which includes Δ¹⁴C as a passive tracer, has been forced with reanalysis fluxes over 1948 � 1999, and the output is compared with a previously reported Galapagos Δ¹⁴C record. The model reproduces the abrupt increase in the seasonally minimum Δ¹⁴C in 1976/77 found in the data. This increase is associated with neither a shift of thermocline depth over the NINO3 region, nor a change in the relative proportion of Northern/Southern source waters. Rather, it is due to a decrease in the Sub-Antarctic Mode Water (SAMW) component of the upwelling water, thereby representing a decrease in entrainment of water from below the base of the directly ventilated thermocline.
Rodgers, K. B., P. Friedrichs, and M. Latif, 2004: Tropical Pacific Decadal Variability and Its Relation to Decadal Modulations of ENSO. Journal of Climate, 17(19), doi:10.1175/1520-0442(2004)017<3761:TPDVAI>2.0.CO;2 3761-3774
[ Abstract ]
A 1000-yr integration of a coupled ocean�atmosphere model (ECHO-G) has been analyzed to describe decadal to multidecadal variability in equatorial Pacific sea surface temperature (SST) and thermocline depth (Z20), and their relationship to decadal modulations of El Nin�o�Southern Oscillation (ENSO) behavior. Although the coupled model is characterized by an unrealistically regular 2-yr ENSO period, it exhibits significant modulations of ENSO amplitude on decadal to multidecadal time scales. The authors� main finding is that the structures in SST and Z20 characteristic of tropical Pacific decadal variability (TPDV) in the model are due to an asymmetry between the anomaly patterns associated with the model�s El Nin�o and La Nin�a states, with this asymmetry reflecting a nonlinearity in ENSO variability. As a result, the residual (i.e., the sum) of the composite El Nin�o and La Nin�a patterns exhibits a nonzero dipole structure across the equatorial Pacific, with positive perturbation values in the east and negative values in the west for SST and Z20. During periods when ENSO variability is strong, this difference manifests itself as a rectified change in the mean state. For comparison, a similar analysis was applied to a gridded SST dataset spanning the period 1871�1999. The data confirms that the asymmetry between the SST anomaly patterns associated with El Nin�o and La Nin�a for the model is realistic. However, ENSO in the observations is weaker and not as regular as in the model, and thus the changes due to ENSO asymmetries for the observations can only be detected in the Nin�o-12 region.
Rodgers, K. B., S. Charbit, M. Kageyama, G. Philippon, G. Ramstein, C. Ritz, J. H. Yin, G. Lohmann, S. J. Lorenz, and M. Khodri, 2004: Sensitivity of Northern Hemispheric continental ice sheets to tropical SST during deglaciation. Geophysical Research Letters, 31(L02206), doi:10.1029/2003GL018375
[ Abstract ]
A thermomechanical ice sheet model (ISM) is used to investigate the sensitivity of the Laurentide and Fennoscandian ice sheets to tropical sea surface temperature (SST) perturbations during deglaciation. The ISM is driven by surface temperature and precipitation fields from three different atmospheric general circulation models (AGCMs). For each AGCM, the responses in temperature and precipitation over the ice sheets nearly compensate, such that ice sheet mass balance is not strongly sensitive to tropical SST boundary conditions. It was also found that there is significant variation in the response of the ISM to the different AGCM output fields.
Sandin, S. A., and Stephen W. Pacala, 2004: Regulation in populations of coral reef fish: an exploration of models and data. Proceedings of the Ninth International Coral Reef Symposium, Bali, Indonesia, http://cmbc.ucsd.edu/content/1/docs/Sandin_Pacala_final_9ICRS.pdf, 455-462
[ Abstract ]
The study of population regulation in reef fish populations is confounded by large amounts of stochasticity obscuring patterns in the field. We analyze a series of population models, comparing equilibrial solutions under conditions of top-down and bottom-up regulation. We also treat patterns of population variance that will be expected as recruitment variance is propagated through to adult populations. We find that predators affect reef fish populations by absorbing recruitment variance across space and through time. Food limitation will instead reduce fluctuations of adult fish biomass through time. Our model suggests that the study of regulation cannot be conducted through counting fish alone, but requires measurement of biomass simultaneously. By surveying fish across natural and human-created clines of recruitment and mortality, we can focus fieldwork on testing focused predictions of regulation on coral reefs.
Sarmiento, Jorge, R. D. Slater, R. Barber, L. Bopp, S. C. Doney, A. C. Hirst, J. Kleypas, R. J. Matear, U. Mikolajewicz, P. Monfray, V. Soldatov, S. A. Spall, and R. J. Stouffer, 2004: Response of ocean ecosystems to climate warming. Global Biogeochemical Cycles, GB3003, doi:10.1029/2003GB002134
[ Abstract ]
We examine six different coupled climate model simulations to determine the ocean biological response to climate warming between the beginning of the industrial revolution and 2050. We use vertical velocity, maximum winter mixed layer depth, and sea ice cover to define six biomes. Climate warming leads to a contraction of the highly productive marginal sea ice biome by 42% in the Northern Hemisphere and 17% in the Southern Hemisphere, and leads to an expansion of the low productivity permanently stratified subtropical gyre biome by 4.0% in the Northern Hemisphere and 9.4% in the Southern Hemisphere. In between these, the subpolar gyre biome expands by 16% in the Northern Hemisphere and 7% in the Southern Hemisphere, and the seasonally stratified subtropical gyre contracts by 11% in both hemispheres. The low-latitude (mostly coastal) upwelling biome area changes only modestly. Vertical stratification increases, which would be expected to decrease nutrient supply everywhere, but increase the growing season length in high latitudes. We use satellite ocean color and climatological observations to develop an empirical model for predicting chlorophyll from the physical properties of the global warming simulations. Four features stand out in the response to global warming: (1) a drop in chlorophyll in the North Pacific due primarily to retreat of the marginal sea ice biome, (2) a tendency toward an increase in chlorophyll in the North Atlantic due to a complex combination of factors, (3) an increase in chlorophyll in the Southern Ocean due primarily to the retreat of and changes at the northern boundary of the marginal sea ice zone, and (4) a tendency toward a decrease in chlorophyll adjacent to the Antarctic continent due primarily to freshening within the marginal sea ice zone. We use three different primary production algorithms to estimate the response of primary production to climate warming based on our estimated chlorophyll concentrations. The three algorithms give a global increase in primary production of 0.7% at the low end to 8.1% at the high end, with very large regional differences. The main cause of both the response to warming and the variation between algorithms is the temperature sensitivity of the primary production algorithms. We also show results for the period between the industrial revolution and 2050 and 2090.
Sarmiento, Jorge, N. Gruber, M. A. Brezeinski, and J. P. Dunne, 2004: High latitude controls of thermodine nutrients and low latitude biological productivity. Nature, 427, doi:10.1038/nature02127 56-60
[ Abstract ]
The ocean�s biological pump strips nutrients out of the surface waters and exports them into the thermocline and deep waters. If there were no return path of nutrients from deep waters, the biological pump would eventually deplete the surface waters and thermocline of nutrients; surface biological productivity would plummet. Here we make use of the combined distributions of silicic acid and nitrate to trace the main nutrient return path from deep waters by upwelling in the Southern Ocean1 and subsequent entrainment into subantarctic mode water. We show that the subantarctic mode water, which spreads throughout the entire Southern Hemisphere 2,3 and North Atlantic Ocean3, is the main source of nutrients for the thermocline. We also find that an additional return path exists in the northwest corner of the Pacific Ocean, where enhanced vertical mixing, perhaps driven by tides4, brings abyssal nutrients to the surface and supplies them to the thermocline of the North Pacific. Our analysis has important implications for our understanding of large-scale controls on the nature and magnitude of low-latitude biological productivity and its sensitivity to climate change.
Sigman, Daniel, S. L. Jaccard, and G. H. Haug, 2004: Polar ocean stratification in a cold climate. Nature, 428, doi:10.1038/nature02357 59-63
[ Abstract ]
The low-latitude ocean is strongly stratified by the warmth of its surface water. As a result, the great volume of the deep ocean has easiest access to the atmosphere through the polar surface ocean. In the modern polar ocean during the winter, the vertical distribution of temperature promotes overturning, with colder water over warmer, while the salinity distribution typically promotes stratification, with fresher water over saltier. However, the sensitivity of seawater density to temperature is reduced as temperature approaches the freezing point, with potential consequences for global ocean circulation under cold climates1,2. Here we present deep-sea records of biogenic opal accumulation and sedimentary nitrogen isotopic composition from the Subarctic North Pacific Ocean and the Southern Ocean. These records indicate that vertical stratification increased in both northern and southern high latitudes 2.7 million years ago, when Northern Hemisphere glaciation intensified in association with global cooling during the late Pliocene epoch. We propose that the cooling caused this increased stratification by weakening the role of temperature in polar ocean density structure so as to reduce its opposition to the stratifying effect of the vertical salinity distribution. The shift towards stratification in the polar ocean 2.7 million years ago may have increased the quantity of carbon dioxide trapped in the abyss, amplifying the global cooling.
Socolow, Robert H., R. Hotinski, J. B. Greenblatt, and Stephen W. Pacala, December 2004: Solving the Climate Problem: Technologies Available to Curb CO₂ Emissions. Environment, http://www.princeton.edu/~cmi/resources/CMI_Resources_new_files/Environ_08-21a.pdf, 46(10), 8-19
[ Abstract ]
The atmosphere�s concentration of carbon dioxide (CO₂) has increased by more than 30 percent over the last 250 years, largely due to human activity. Two-thirds of that rise has occurred in the past 50 years.1 Unless there is a change, the world will see much higher CO₂ levels in the future�levels that are predicted to lead to damaging climate change. Fortunately, many carbon mitigation strategies are available to set the world on a new path, one that leads to a lower rate of CO₂ emissions than is currently expected. The environmental community is currently playing a prominent role in the development of the CO₂ policies that will elicit these strategies. Until a few years ago, the environmental community was almost exclusively interested in policies that promote renewable energy, conservation, and natural sinks. More recently, it has begun to explore alliances with traditional energy supply industries on the grounds that to establish the pace required to achieve environmental goals, parallel action on many fronts is required.
Socolow, Robert H., 2004: co-author, The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs. Board of Energy and Environmental Systems, Washington, DC, National Academy Press, (ISBN - 10:0-309-0916),
[ Abstract ]
The announcement of a hydrogen fuel initiative in the President�s 2003 State of the Union speech substantially increased interest in the potential for hydrogen to play a major role in the nation�s long-term energy future. Prior to that event, DOE asked the National Research Council to examine key technical issues about the hydrogen economy to assist in the development of its hydrogen R&D program. Included in the assessment were the current state of technology; future cost estimates; CO₂ emissions; distribution, storage, and end use considerations; and the DOE RD&D program. The report provides an assessment of hydrogen as a fuel in the nation�s future energy economy and describes a number of important challenges that must be overcome if it is to make a major energy contribution. Topics covered include the hydrogen end-use technologies, transportation, hydrogen production technologies, and transition issues for hydrogen in vehicles.
Socolow, Robert H., Stephen W. Pacala, and J. B. Greenblatt, September 2004: Wedges: Early Mitigation with Familiar Technology. Proceedings of the 7th International Conference on Greenhouse Gas Control Technologies, (GHGT-7), http://www.princeton.edu/~cmi/research/Vancouver04/socolow%20poster.pdf,
[ Abstract ]
If the world is willing to accept a tripling of the pre-industrial atmospheric CO₂ concentration, significant carbon mitigation can be delayed for most of the next half century. If the world is to be put on a path to avoid a doubling, however, a monumental mitigation effort needs to start now. To convey the magnitude of the effort, we introduce the �wedge� as the unit of mitigation: a wedge is an activity that creates 1 GtC/y of carbon emission reductions in 2054, relative to a world unconcerned about global carbon emissions. To pursue 500 ppm stabilization, the task for the next 50 years is to achieve about seven wedges by avoiding about 175 billion tons of carbon emissions.
Baidya Roy, S., G. C. Hurtt, C. P. Weaver, and Stephen W. Pacala, 2003: Impact of historical land cover change on the July climate of the United States. Journal of Geophysical Research, 108(D24), doi:10.1029/2003JD003565
[ Abstract ]
We used the Regional Atmospheric Modeling System (RAMS) model to investigate the possible impact of land cover change on the July climate of the coterminous United States over the last 290 years. Vegetation data were estimated using the Ecosystem Demography model. The observed change in land cover leads to a weak warming along the Atlantic coast and a strong cooling of more than 1 K over the Midwest and the Great Plains region. The precipitation signal is weaker and shows some reduction in the Midwest because of changes in the patterns of large-scale moisture advection.
Bender, Michael, 2003: Climate-biosphere interactions on glacial-interglacial timescales. Global Biogeochemical Cycles, 17(3), doi:10.1029/2002GB001932
[ Abstract ]
Potential positive feedbacks of the biosphere on glacial-interglacial climate change have been extensively investigated in recent years. In this paper, we summarize these feedbacks and the evidence that they may play a quantitatively significant role. We then attempt to assess the role of biosphere feedbacks in glacial/interglacial climate change by evaluating five lines of empirical evidence: (1) synchroneity of warming during the last glacial termination (expected if the biosphere is important, because of short response times); (2) changes in the δ¹⁸O of O₂, which may reflect the relative fertility of the land and ocean biospheres, (3) changes in the triple isotope composition of O₂, which constrain global rates of photosynthesis in the past; (4) the relationship between atmospheric CO₂ and dust accumulation at Vostok, and (5) indications for the occurrence or absence of Pleistocene-style glacial cycles before the evolution of the land biosphere. The evidence is compatible with a significant role for the biosphere in driving glacial-interglacial change, but unambiguous empirical support is not yet in hand.
Bolker, B. M., Stephen W. Pacala, and C. Neuhauser, 2003: Spatial dynamics in model plant communities: what do we really know? American Naturalist, 162(2), doi:10.1086/376575 135-148
[ Abstract ]
A variety of models have shown that spatial dynamics and small-scale endogenous heterogeneity (e.g., forest gaps or local resource depletion zones) can change the rate and outcome of competition in communities of plants or other sessile organisms. However, the theory appears complicated and hard to connect to real systems. We synthesize results from three different kinds of models: interacting particle systems, moment equations for spatial point processes, and metapopulation or patch models. Studies using all three frameworks agree that spatial dynamics need not enhance coexistence nor slow down dynamics; their effects depend on the underlying competitive interactions in the community. When similar species would coexist in a nonspatial habitat, endogenous spatial structure inhibits coexistence and slows dynamics. When a dominant species disperses poorly and the weaker species has higher fecundity or better dispersal, competition-colonization tradeoffs enhance coexistence. Even when species have equal dispersal and per-generation fecundity, spatial successional niches where the weaker and faster-growing species can rapidly exploit ephemeral local resources can enhance coexistence. When interspecific competition is strong, spatial dynamics reduce founder control at large scales and short dispersal becomes advantageous. We describe a series of empirical tests to detect and distinguish among the suggested scenarios.
Gao, Y., S.-M. Fan, and Jorge Sarmiento, 2003: Aeolian iron input to the ocean through precipitation scavenging: a modeling perspective and its implication for natural iron fertilization in the ocean. Journal of Geophysical Research, 108((D7)4221), doi:10.1029/2002JD002420
[ Abstract ]
Aeolian dust input may be a critical source of dissolved iron for phytoplankton growth in some oceanic regions. We used an atmospheric general circulation model (GCM) to simulate dust transport and removal by dry and wet deposition. Model results show extremely low dust concentrations over the equatorial Pacific and Southern Ocean. We find that wet deposition through precipitation scavenging accounts for ~40% of the total deposition over the coastal oceans and ~60% over the open ocean. Our estimates suggest that the annual input of dissolved Fe by precipitation scavenging ranges from 0.5 to 4 X 10¹² g yr^-1, which is 4 � 30% of the total aeolian Fe fluxes. Dissolved Fe input through dry deposition is significantly lower than that by wet deposition, accounting for only 0.6 � 2.4 % of the total Fe deposition. Our upper limit estimate on the fraction of dissolved Fe in the total atmospheric deposition is thus more than three times higher than the value of 10% currently considered as an upper limit for dissolved Fe in Aeolian fluxes. As iron input through precipitation may promote episodic phytoplankton growth in the ocean, measurements of dissolved iron in rainwater over the oceans are needed for the study of oceanic biogeochemical cycles.
Gnanadesikan, A., Jorge Sarmiento, and R. D. Slater, 2003: Effects of patchy ocean fertilization on atmospheric carbon dioxide and biological production. Global Biogeochemical Cycles, 17(2), doi:10.1029/2002GB001940
[ Abstract ]
Increasing oceanic productivity by fertilizing nutrient-rich regions with iron has been proposed as a mechanism to offset anthropogenic emissions of carbon dioxide. Earlier studies examined the impact of large-scale fertilization of vast reaches of the ocean for long periods of time. We use an ocean general circulation model to consider more realistic scenarios involving fertilizing small regions (a few hundred kilometers on a side) for limited periods of time (of order 1 month). A century after such a fertilization event, the reduction of atmospheric carbon dioxide is between 2% and 44% of the initial pulse of organic carbon export to the abyssal ocean. The fraction depends on how rapidly the surface nutrient and carbon fields recover from the fertilization event. The modeled recovery is very sensitive to the representation of biological productivity and remineralization. Direct verification of the uptake would be nearly impossible since changes in the air-sea flux due to fertilization would be much smaller than those resulting from natural spatial variability. Because of the sensitivity of the uptake to the long-term fate of the iron and organic matter, indirect verification by measurement of the organic matter flux would require high vertical resolution and long-term monitoring. Finally, the downward displacement of the nutrient profile resulting from an iron-induced productivity spurt may paradoxically lead to a long-term reduction in biological productivity. In the worst-case scenario, removing 1 ton of carbon from the atmosphere for a century is associated with a 30-ton reduction in biological export of carbon.
Gurney, K. R., R. M. Law, A. S. Denning, P. J. Rayner, D. Baker, P. Bousquet, L. Bruhwiler, Y.-H. Chen, P. Ciais, Y. Fan, I. Y. Fung, and M. N. Gloor, 2003: TransCom 3 CO₂ inversion intercomparison: 1. Annual mean control results and sensitivity to transport and prior flux information. Tellus, Series B, International Meteorological Institute in Stockholm, 55(2), doi:10.1034/j.1600-0889.2003.00049.x 555-579
[ Abstract ]
Spatial and temporal variations of atmospheric CO₂ concentrations contain information about surface sources and sinks, which can be quantitatively interpreted through tracer transport inversion. Previous CO₂ inversion calculations obtained differing results due to different data, methods and transport models used. To isolate the sources of uncertainty, we have conducted a set of annual mean inversion experiments in which 17 different transport models or model variants were used to calculate regional carbon sources and sinks from the same data with a standardized method. Simulated transport is a significant source of uncertainty in these calculations, particularly in the response to prescribed �background� fluxes due to fossil fuel combustion, a balanced terrestrial biosphere, and air�sea gas exchange. Individual model-estimated fluxes are often a direct reflection of their response to these background fluxes. Models that generate strong surface maxima near background exchange locations tend to require larger uptake near those locations. Models with weak surface maxima tend to have less uptake in those same regions but may infer small sources downwind. In some cases, individual model flux estimates cannot be analyzed through simple relationships to background flux responses but are likely due to local transport differences or particular responses at individual CO₂ observing locations. The response to the background biosphere exchange generates the greatest variation in the estimated fluxes, particularly over land in the Northern Hemisphere. More observational data in the tropical regions may help in both lowering the uncertain tropical land flux uncertainties and constraining the northern land estimates because of compensation between these two broad regions in the inversion. More optimistically, examination of the model-mean retrieved fluxes indicates a general insensitivity to the prior fluxes and the prior flux uncertainties. Less uptake in the Southern Ocean than implied by oceanographic observations, and an evenly distributed northern land sink, remain in spite of changes in this aspect of the inversion setup.
Hastings, M. G., Daniel Sigman, and R. Lipshultz, 2003: Isotopic evidence for source changes of nitrate in rain at Bermuda. Journal of Geophysical Research � Atmosphere, 108(D24), doi:10.1029/2003JD003789
[ Abstract ]
Rainwater collected on the island of Bermuda between January 2000 and January 2001 shows pronounced seasonal variation in the nitrogen and oxygen isotopic composition of nitrate. Higher ¹⁵N/¹⁴N and lower ¹⁸O/¹⁶O ratios are observed in the warm season (April�September) in comparison to the cool season (October�March): The mean d15N of nitrate for the warm and cool seasons is -2.1% and -5.9% (versus air N2), respectively, while the mean δ:¹⁸O is 68.6% and 76.9% (versus Vienna Standard Mean Ocean Water). The few cool season rain events that had high ¹⁵N/¹⁴N and low ¹⁸O/¹⁶O exhibited trajectory paths originating from the south, similar to those of warm season samples. Accordingly, the region from which air is transported to the island determines the ¹⁵N/¹⁴N and ¹⁸O/¹⁶O of the nitrate. The source region provides precursor nitrogen oxides (NO_x), influencing the ¹⁵N/¹⁴N of nitrate, and contributes to the chemistry that produces nitrate from NO_x, which determines the ¹⁸O/¹⁶O of nitrate. While the range in nitrate ¹⁵N/¹⁴N observed during the cool season is consistent with anthropogenic emissions from North America, the higher warm season ¹⁵N/¹⁴N suggests that lightning is a significant source of nitrate to Bermuda. The isotopic evidence for a significant southern source of nitrate to Bermuda helps to explain the previous observation of unexpectedly high nitrate concentrations in warm season rain. The ¹⁸O/¹⁶O of nitrate in rain at Bermuda is high throughout the year (δ:¹⁸O = 60.3 to 86.5%) as a result of interactions of precursor NO_x with ozone, which has a high ¹⁸O/¹⁶O ratio. The lower nitrate ¹⁸O/¹⁶O in the warm season and in cool season air masses from the south is consistent with elevated concentrations of hydroxyl radical (OH), which dilutes the isotopic signal of ozone. Our limited data set suggests that the relative importance of the OH sink for NO_x during the cool season varies spatially over as large a range as is observed between the warm and cool seasons.
Karsh, K. L., T. W. Trull, M. J. Lourey, and Daniel Sigman, 2003: Relationship of nitrogen isotope fractionation to phytoplankton size and iron availability during the SOIREE Southern Ocean Iron Release Experiment. Limnology and Oceanography, http://www.aslo.org/lo/toc/vol_48/issue_3/1058.pdf, 48(3), 1058-1068
[ Abstract ]
The ¹⁵N composition of sediments has been used as a proxy for nitrate utilization in surface waters to assess the role of Southern Ocean export production in glacial/interglacial changes in atmospheric CO₂ concentration. Interpretation has relied on a temporally constant isotope effect (ε) associated with uptake and assimilation of nitrate by phytoplankton. To investigate the reliability of this approach, we examined the relationships between the ¹⁵N compositions of dissolved nitrate, bulk and size-fractionated (200, 70, 20, 5, 1 �m) suspended particulate organic nitrogen (PON), and sinking particles obtained from sediment traps during the Southern Ocean iron release experiment (SOIREE). We found variations in phytoplankton nitrogen isotopic compositions with both cell size and iron availability. δ¹⁵N_PON increased by .2� with increasing size, both within and outside the iron enriched patch. In comparison to unfertilized waters, δ¹⁵N_PON within the iron-fertilized patch was a further 3�4� higher in those size fractions dominated by large diatoms (20�70, 70�200 �mm). We speculate that this iron response might result from (1) variation in � of nitrate utilization or (2) an iron-stimulated shift from ammoniumbased to nitrate-based production. Comparing the δ¹⁵N_PON of the large diatom�dominated size fractions to the δ¹⁵N_PON of nitrate suggests relatively low ε values of 4�5�, in contrast to estimated values of 7�10� from seasonal nitrate depletion and export production. This suggests that higher glacial δ¹⁵N in Southern Ocean sediments could, in part, reflect increases in iron availability, dominant cell size, and possibly growth rates, and these effects must be considered in any quantitative scaling of δ¹⁵N variations, including those of diatom-bound δ¹⁵N, to the extent of nitrate utilization.
Kinzig, A. P., D. Starrett, K. Arrow, S. Aniyar, B. Bolin, P. Dasgupta, P. Ehrlich, C. Folke, M. Hanemann, G. Heal, M. Hoel, and A. Jansson, et al., 2003: Coping with Uncertainty: A Call for a New Science-Policy Forum. Royal Swedish Academy of Sciences, http://ambio.allenpress.com/archive/0044-7447/32/5/pdf/i0044-7447-32-5-330.pdf, Ambio 32(5), 330-335
[ Abstract ]
The scientific and policy worlds have different goals, which can lead to different standards for what constitutes �proof� of a change or phenomena, and different approaches for characterizing and conveying uncertainty and risk. These differences can compromise effective communication among scientists, policymakers, and the public, and constrain the types of socially compelling questions scientists are willing to address. In this paper, we review a set of approaches for dealing with uncertainty, and illustrate some of the errors that arise when science and policy fail to coordinate correctly. We offer a set of recommendations, including restructuring of science curricula and establishment of science-policy forums populated by leaders in both arenas, and specifically constituted to address problems of uncertainty.
Kraepiel, A. M., Klaus Keller, H. B. Chin, E. G. Malcolm, and Francois Morel, 2003: Sources and Variations of Mercury in Tuna. Environmental Science and Technology, 37, doi:10.1021/es0340679 5551-5558
[ Abstract ]
While the bulk of human exposure to mercury is through the consumption of marine fish, most of what we know about mercury methylation and bioaccumulation is from studies of freshwaters. We know little of where and how mercury is methylated in the open oceans, and there is currently a debate whether methylmercury concentrations in marine fish have increased along with global anthropogenic mercury emissions. Measurements of mercury concentrations in Yellowfin tuna caught off Hawaii in 1998 show no increase compared to measurements of the same species caught in the same area in 1971. On the basis of the known increase in the global emissions of mercury over the past century and of a simple model of mercury biogeochemistry in the Equatorial and Subtropical Pacific ocean, we calculate that the methylmercury concentration in these surface waters should have increased between 9 and 26% over this 27 years span if methylation occurred in the mixed layer or in the thermocline. Such an increase is statistically inconsistent with the constant mercury concentrations measured in tuna. We conclude tentatively that mercury methylation in the oceans occurs in deep waters or in sediments.
Law, R. M., Y.-H. Chen, K. R. Gurney, and 3 Transcom, 2003: TransCom 3 CO₂ inversion intercomparison: 2. Sensitivity of annual mean results to data choices. Tellus, [B], 55(2), 580-595
[ Abstract ]
TransCom 3 is an intercomparison project for CO₂ source inversions. Annual mean CO₂ concentration data are used to estimate CO₂ sources using 16 different atmospheric transport models. Here we test the sensitivity of the inversion to the concentration data. We examine data network choice, time period of data, baseline data selection and the choice of data uncertainty used.We find that in most cases regional source estimates lie within the source uncertainty range of the control inversion. This indicates that the estimated sources are relatively insensitive to the changes in data that were tested. In the data network tests, only the Australian region source estimates varied over a much larger range than that given by the control case uncertainty estimate. For the other regions, the sensitivity to data network was within or close to the uncertainty range. Most of the sensitivity was found to be associated with a small number of sites (e.g. Darwin, Easter Island). These sites are often identified by the inability of the inversion to fit the data at these locations. The model-mean inversion values are mostly insensitive to the time period of data used, with the exception of temperate North America and the tropical Indian ocean. Data selection has a small impact on source estimates for the mean across models, but individual model sensitivity can be large. The magnitude of data uncertainties controls the relative magnitude of the estimated source uncertainty and the spread in model source estimates. Smaller data uncertainties lead to larger differences in source estimates between models. Overall, the data sensitivity tests performed here support the robustness of the control inversion source estimates presented in Gurney et al. (2003. Tellus 55B, this issue). The test results also provide guidance in setting up and interpreting other inversions.
Levin, S. A., and Stephen W. Pacala, 2003: Ecosystem Dynamics. Handbook of Environmental Economics, North Holland, Amsterdam, Elsevier, 1, doi:10.1016/S1574-0099(03)01007-6 61-95
[ Abstract ]
From ecosystems we derive food and fiber, fuel and pharmaceuticals. Ecosystems mediate local and regional climates, stabilize soils, purify water, and in general provide a nearly endless list of services essential to life as we know it. To understand how to manage these services it is essential to understand how ecological communities are organized and how to measure the biological diversity they contain. Ecological communities are comprised of many species, which are in turn made up of large numbers of individuals, each with their own separate ecological and evolutionary agendas. Not all species are equal as regards their role in maintaining the functioning of ecosystems or their resiliency in the face of stress. This chapter explains how ecosystems evolve and function as complex adaptive systems. It examines ecological systems at scales from the small to the large, from the individual to the collective to the community, from the leaf to the plant to the biosphere (including the global carbon cycle). It reviews theoretical and empirical models of ecosystem dynamics, which are highly nonlinear and contain the potential for qualitative and irreversible shifts. It considers applications to forests, fisheries, grasslands, and freshwater lakes.
Lourey, M. J., T. W. Trull, and Daniel Sigman, 2003: Sensitivity of δ15N of nitrate, surface suspended and deep sinking particulate nitrogen to seasonal nitrate depletion in the Southern Ocean. Global Biogeochemical Cycles, 17(3), doi:10.1029/2002GB001973
[ Abstract ]
We report measurements of the δ¹⁵N of nitrate, suspended particulate nitrogen (PN), and sinking PN from cruises and moored sediment traps in the Subantarctic Zone (SAZ) and Polar Frontal Zone (PFZ) south of Australia. As expected, surface water nitrate δ¹⁵N increased as nitrate was consumed during the spring/summer bloom. In contrast, the seasonal cycles of surface water suspended and sinking PN δ¹⁵N did not fit expectations from nitrate assimilation alone. Rather than increasing, the δ¹⁵N of surface suspended PN was relatively constant in the SAZ (at ~1%), and decreased during the summer in the PFZ (from ~0 to ~-4%), most likely due to the production of low ¹⁵N PN by summertime ammonium recycling. Deep sediment trap PN δ¹⁵N also displayed seasonal decreases (from ~4 to ~1% in the SAZ, and from ~3.5 to ~0.5% in the PFZ), which correlated with PON flux magnitude. During high-flux periods, exported PN δ¹⁵N values were close to expectations from nitrate-based export, but low-flux periods exhibited higher δ¹⁵N, consistent with either a reduction in the isotope effect of nitrate assimilation or more extensive isotopic alteration of the sinking material during low-flux periods. The mass balance between net nitrate supply and exported PN that links sinking flux δ¹⁵N to nitrate utilization requires only that the annually integrated (rather than the seasonally varying) sinking flux of PN δ¹⁵N correlates with nitrate depletion. While a correlation between annually integrated sinking PN δ¹⁵N to nitrate depletion was observed in both the SAZ and PFZ, the sensitivity of sinking PN δ¹⁵N to nitrate depletion was lower than expected. Moreover, the seasonal observations raise the possibility that loss of the summertime high-flux period represents an alternative explanation to increased nitrate utilization for the high sedimentary PN δ¹⁵N observed during glacial periods.
Maksyutov, S. T., T. Machida, H. Mukai, P. K. Patra, T. Nakazawa, G. Inoue, and 3 Transcom, 2003: Effect of recent observations on Asian CO₂ flux estimates with transport model inversions. Tellus, 55(2), 522-529
[ Abstract ]
We use an inverse model to evaluate the effects of the recent CO₂ observations over Asia on estimates of regional CO₂ sources and sinks. Global CO₂ flux distribution is evaluated using several atmospheric transport models, atmospheric CO₂ observations and a �time-independent� inversion procedure adopted in the basic synthesis inversion by the Transcom-3 inverse model intercomparison project. In our analysis we include airborne and tower observations in Siberia, continuous monitoring and airborne observations over Japan, and airborne monitoring on regular flights on Tokyo�Sydney route. The inclusion of the new data reduces the uncertainty of the estimated regional CO₂ fluxes for Boreal Asia (Siberia), Temperate Asia and South-East Asia. The largest effect is observed for the emission/sink estimate for the Boreal Asia region, where introducing the observations in Siberia reduces the source uncertainty by almost half. It also produces an uncertainty reduction for Boreal North America. Addition of the Siberian airborne observations leads to projecting extra sinks in Boreal Asia of 0.2 Pg C yr^-1, and a smaller change for Europe. The Tokyo�Sydney observations reduce and constrain the Southeast Asian source.
Mann, M. E., C. M. Ammann, R. S. Bradley, K. R. Briffa, T. J. Crowley, M. K. Hughes, P. D. Jones, Michael Oppenheimer, T. J. Osborn, J. T. Overpeck, S. Rutherford, K. E. Trenberth, and T.M.L. Wigley, 2003: On past temperatures and anomalous late-20th century warmth. EOS Trans. AGU, 84, doi:10.1029/2003EO270003 256
[ Abstract ]
Evidence from paleoclimatic sources and modeling studies support AGU's official position statement on "Climate Change and Greenhouse Gases," that there is a compelling basis for concern over future climate changes, including increases in global-mean surface temperatures, due to increased concentrations of greenhouse gases, primarily from fossil-fuel burning. More specifically, a number of reconstructions of large-scale temperature changes over the past millennium support the conclusion that late-20th century warmth was unprecedented over at least the past millennium. Modeling and statistical studies indicate that such anomalous warmth cannot be fully explained by natural factors but, instead, require a significant anthropogenic forcing of climate that emerged during the 19th and 20th centuries.
Two (nearly identical) recent papers [Soon and Baliunas, 2003 and Soon et al., 2003--henceforth both referred to as 'SB03'] challenge this view, and have been used to support the claim that recent hemispheric-scale warmth is not unprecedented in the context of the past millennium (see e.g. "20th Century Climate Not So Hot", press-release, Harvard-Smithsonian Center for Astrophysics, March 31, 2003: http://cfa-www.harvard.edu/press/pr0310.html). Such claims are inconsistent with the preponderance of scientific evidence. We therefore review these claims in the light of the fact that they have found their way into the media and have been read into the U.S. Senate record.
McKinley, G., R. J. Matear, R. M. Key, J. L. Bullister, and Jorge Sarmiento, 2003: Anthropogenic CO₂ uptake by the ocean based on the global chlorofluorocarbon dataset. Science, 299, doi:10.1126/science.1077429 235-239
[ Abstract ]
We estimated the oceanic inventory of anthropogenic carbon dioxide (CO₂) from 1980 to 1999 using a technique based on the global chlorofluorocarbon data set. Our analysis suggests that the ocean stored 14.8 petagrams of anthropogenic carbon from mid-1980 to mid-1989 and 17.9 petagrams of carbon from mid-1990 to mid-1999, indicating an oceanwide net uptake of 1.6 and 2.0 � 0.4 petagrams of carbon per year, respectively. Our results provide an upper limit on the solubility-driven anthropogenic CO₂ flux into the ocean, and they suggest that most ocean general circulation models are overestimating oceanic anthropogenic CO₂ uptake over the past two decades.
Oppenheimer, Michael, 2003: Atmospheric Pollution: History, Science, and Regulation. Physics Today, http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=p, 56, 65-66
[ Abstract ]
Scientific and political interest in atmospheric pollution, as well as attempts to regulate it, have expanded from local to regional to global scales over the three decades since the passage of the US Clean Air Act of 1970. Acid deposition, ozone depletion, regional-scale smog, and global warming � unknown or little understood before 1970 � are at the center of atmospheric research, domestic regulation, and international affairs. With regard to international affairs, witness the broad effect on US-European relations of the Bush administration�s rejection of the Kyoto Protocol on climate change.
Oppenheimer, Michael, and A. Petsonk, 2003: Global Warming: Formulating Long Term Goals. Climate Policy Beyond Kyoto: Meeting the Long Term Challenge of Global Warming, http://www.princeton.edu/~cmi/research/Policy/Papers/oppenheimer.pdf,
[ Abstract ]
In this paper we explore the origins and potential implementation of long term climate objectives and the particular concept of �dangerous anthropogenic interference with the climate system,� outlined in Article 2 of the Framework Convention. We show that the need for a long term perspective and also its specific framing in the form of Article 2 reflects views held on both sides of the Atlantic from the earliest days of the climate issue. We review the evolution of the concept of �dangerous� and the various proposals for implementing Article 2 as a regulatory regime. It is here that we find the greatest potential for transatlantic differences, arising from differing governmental views on risk and uncertainty. We argue that these potential differences need to be addressed quickly so that current conceptions of what constitutes �dangerous� can play a significant role in determining near term, as well as long-term, climate policy. That is, policy approaches that address �stabilization of concentrations� and those that address near term emissions limitations should be considered together.
Pacala, Stephen W., E. Bulte, J. A. List, and S. A. Levin, 2003: False Alarm over Environmental False Alarms. Science, 301, doi:10.1126/science.1086646 1187-1188
[ Abstract ]
We live in an uncertain world, in which action and prudence must be continually juggled. Caution can be costly, but indifference to serious risks can be disastrous. In all aspects of life, we weigh risks and benefits, invoking measures to insure against events that threaten what is most important to us, while gambling with those that can be tolerated. In matters of our environment, science has the responsibility to inform these decisions, and society must find ways to identify the appropriate level of circumspection. By any calculation, we must protect ourselves against a wide variety of events that individually have low probabilities of occurrence, and still feel good when they have not occurred. We must rely on environmental science to alert us to an even wider set of possible disasters, many of very low probability, so that we as citizens can decide which cause us most worry, and which mandate action.
Patra, P. K., S. T. Maksyutov, and 3 Transcom, 2003: Sensitivity of optimal extension of CO₂ observation networks to the model transport. Tellus, 55(2), 498-511
[ Abstract ]
Optimal extensions of the surface CO₂ observation network have been determined using 15 global transport models and a time-independent inverse model. The regional average CO₂ flux estimate uncertainty is minimized based on theTransCom-3 (level 1) framework.Anensemble model calculation shows that the regional average CO₂ flux uncertainties could be reduced to about 0.36, 0.32, 0.28 or 0.26 Gt C yr^-1 per region, from about 0.53 Gt C yr^-1 per region corresponding to the basic network, after adding 5, 10, 15 or 20 optimally located stations, respectively. The additional station locations are mostly found in continental South America and Africa. The distribution of the efficiency in estimation of flux uncertainty reduction per station tends to become more uniform with the extension of the network. We show that the multimodel approach to network design converges if a large enough extension is considered; about 20 stations in this inverse model framework. The reduction in the flux uncertainty for the first few stations depends on the model of atmospheric transport, and is nearly proportional to the simulated signal from local emissions in the surface layer. In addition, it is seen that the simulated spatial and temporal variability of CO₂ concentration has significant influence on the distribution of the additional stations as well as determining the regional flux estimate uncertainty.
Sigman, Daniel, and G. H. Haug, 2003: Biological Pump in the Past. Treatise On Geochemistry, Oxford, Elsevier Science, 6, doi:10.1016/B0-08-043751-6/06118-1 492-528
[ Abstract ]
It is easy to imagine that the terrestrial biosphere sequesters atmospheric carbon dioxide; the form and quantity of the sequestered carbon, living or dead organic matter, are striking. In the ocean, there are no aggregations of biomass comparable to the forests on land. Yet biological productivity in the ocean plays a central role in the sequestration of atmospheric carbon dioxide, typically overshadowing the effects of terrestrial biospheric carbon storage on timescales longer than a few centuries. In an effort to communicate the ocean's role in the regulation of atmospheric carbon dioxide, marine scientists frequently refer to the ocean's biologically driven sequestration of carbon as the "biological pump." The original and strict definition of the biological (or "soft-tissue") pump is actually more specific: the sequestration of carbon dioxide in the ocean interior by the biogenic flux of organic matter out of surface waters and into the deep sea prior to decomposition of that organic matter back to carbon dioxide (Volk and Hoffert, 1985) ( Figure 1). The biological pump extracts carbon from the "surface skin" of the ocean that interacts with the atmosphere, presenting a lower partial pressure of carbon dioxide (CO₂) to the atmosphere and thus lowering its CO₂ content.
Sigman, Daniel, S. J. Lehman, and D. W. Oppo, 2003: Evaluating mechanisms of nutrient depletion and ¹³ C enrichment in the intermediate-depth Atlantic during the last ice age. Paleoceanography, 18(3), doi:10.1029/2002PA000818
[ Abstract ]
Using an ocean box model, we have studied the effect of altered circulation on the oceanic distributions of phosphate (PO₄^-3) and the ¹³C/¹²C and ¹⁴C/¹²C of dissolved inorganic carbon to evaluate competing hypotheses for the cause of observed nutrient depletion and ¹³C enrichment at intermediate depths of the Atlantic during the last ice age. Because of ��nutrient trapping�� and limited air-sea carbon isotopic equilibration, the simple imposition of an intense meridional overturning cell in the Atlantic fails to simultaneously lower nutrient concentrations and raise ¹³C/¹²C to observed glacial levels. Export of intermediate water out of the Atlantic causes a basin-to-basin nutrient transfer, thus providing a more efficient mechanism of intermediate-depth Atlantic nutrient depletion and improved carbon isotopic equilibration at low temperatures (i.e., ¹³C enrichment). Although this export adds nutrients to the intermediate depths of the Pacific and Indian Oceans, the simulated glacial intermediate-depth Indo-Pacific is nevertheless moderately depleted in PO₄^-3 relative to the model�s interglacial control, in agreement with consensus paleoceanographic evidence. This Indo-Pacific PO₄^-3 depletion results from our use of a ��glacial base case�� in which nutrient-rich Antarctic Intermediate Water formation is absent as part of the elimination of the modern North-Atlantic-Deep-Water-based ��conveyor�� circulation.
Socolow, Robert H., 2003: Review of DOE�s Vision 21 Research and Development Program, Phase I (contributor) In , Washington, DC, National Academy Press, (ISBN-10: 0-309-08717),
[ Abstract ]
The Vision 21 Program is a relatively new research and development (R&D) program. It is funded through the U.S. Department of Energy�s (DOE�s) Office of Fossil Energy and its National Energy Technology Laboratory (NETL). The Vision 21 Program Plan anticipates that Vision 21 facilities will be able to convert fossil fuels (e.g., coal, natural gas, and petroleum coke) into electricity, process heat, fuels, and/or chemicals cost effectively, with very high efficiency and very low emissions, including of the greenhouse gas carbon dioxide (CO2) (DOE, 1999a). Planning for the program began to take shape in 1998 and 1999. Since then, workshops have been held, proposals for projects have been funded, and roadmaps have been developed for each of the key technologies considered to be part of the Vision 21 effort. Vision 21 is focused on the development of advanced technologies that would be ready for deployment in 2015.
Vision 21 as it currently stands is not per se a line item in the Office of Fossil Energy budget but, rather, a collection of projects that contribute to the technologies required for Vision 21 energy plants. Vision 21 management estimates that about $50 million was expended in fiscal year (FY) 2002 on Vision 21 projects and activities. These projects have come about not only as a result of a Vision 21 solicitation by DOE/NETL but also as an outgrowth of ongoing R&D activities in the traditional Office of Fossil Energy coal and power systems program. Ongoing activities that are oriented to achieving revolutionary rather than evolutionary improvements in performance and cost and that share common objectives with Vision 21 are considered to be part of the Vision 21 Program and activities. Thus, Vision 21 activities must be coordinated across a suite of activities in DOE and NETL programs contained in the Office of Fossil Energy�s R&D programs on coal and power systems. This coordination is partially achieved through a matrix management structure at NETL, and the responsibility for managing Vision 21 is vested in a small steering committee.
The goals of Vision 21 are extremely challenging and ambitious. As noted in the Vision 21 Technology Roadmap, if the program meets its goals, Vision 21 plants would essentially eliminate many of the environmental concerns traditionally associated with the conversion of fossil fuels into electricity and transportation fuels or chemicals (NETL, 2001). Given the importance of fossil fuels, and especially coal, to the economies of the United States and other countries and the need to utilize fossil fuels in an efficient and environmentally acceptable manner, the development of the technologies in the Vision 21 Program is a high priority.
This report contains the results of the second National Research Council (NRC) review of the Vision 21 R&D Program. The first review of the program was conducted by the NRC Committee on R&D Opportunities for Advanced Fossil-fueled Energy Complexes. It resulted in the report Vision 21, Fossil Fuel Options for the Future, which was published in the spring of 2000 (NRC, 2000). At that time, the Vision 21 Program was in an embryonic stage, having been initiated by DOE in 1998-1999. The NRC report contained a number of recommendations for DOE to consider as it moved forward with its program; DOE�s responses to many of these recommendations are considered in Chapter 3. Now, 2 years after the first review, DOE�s Deputy Assistant Secretary for Coal and Power Systems requested that the NRC again review progress and activities in the Vision 21 Program. In response, the NRC formed the Committee to Review DOE�s Vision 21 R&D Program�Phase I. Most of the members of this committee also served on the committee that wrote the earlier report (see Appendix A for committee biographical information).
The present report is organized into three chapters. Chapter 1 introduces the Vision 21 Program and presents background information. Chapter 2 presents strategic recommendations for the program as a whole. Chapter 3 focuses on the individual technologies. This Executive Summary brings forward from Chapter 2 three major issues that the committee believes are of the highest priority from a programwide strategic standpoint�namely, what the focus of the program should be, how it should be empowered to accomplish its goals, and what analytic capabilities it should have to evaluate technological approaches for reaching its goals. At the same time, it reiterates the five most important of the nine recommendations in that chapter. Also, based on the premise that some of the technologies in Chapter 3 are more essential than others to realizing Vision 21 goals, the committee selected five high-priority recommendations from that chapter and reiterates them here in the Executive Summary.
Socolow, Robert H., 2003: The Century-Scale Problem of Carbon Management. The Carbon Dioxide Dilemma: Promising Technologies and Policies. Proceedings of a Symposium, Washington, DC, The National Academies Press, (ISBN-10: 0-309-08921), 11-14
[ Abstract ]
There are six important things to remember about the greenhouse problem and carbon management. 1. The greenhouse problem is a century-scale problem. 2. From a one-century perspective, the characteristics of fossil fuel production look complex and unfamiliar. 3. Hydrogen is intimately connected with carbon management. 4. Early action on the permitting of CO₂ storage sites will reveal many difficult, largely unresolved issues. 5. Carbon management is not a winner-take-all strategy. 6. Carbon management confronts us with ethical issues.
Socolow, Robert H., et al., June 2003: Responses to the invitation to a discussion on the Sao Paulo Declaration. Energy for Sustainable Development, 7(2), doi:10.1016/S0973-0826(08)60351-8 23-24
[ Abstract ]
The invitation in Volume VI No. 2 (June 2002) of Energy for Sustainable Development to readers to discuss the 1984 S�o Paulo Declaration (SPD) on Self-reliant Analysis and Planning was based on two hunches: (1) that in the intervening almost two decades, a large number of energy specialists would have entered the scene with new and interesting points of view on the topic; (2) that a number of new socio-economic and technical factors had emerged to influence the discourse. The extremely encouraging response to the invitation has proved both these hunches right. Even without a comprehensive campaign, 20 comments have been received before going to press and at least another 5 would have made it given another week or so. Without any deliberate planning, ESD has acted as a forum for energy professionals to discuss a topic of widespread concern. At the same time, the responses have identified a number of new developments that necessitate an amendment and/or extension of the original declaration. What follows below is a synthesis based on the responses and almost wholly consisting of excerpts[1] from them. The full text of the individual comments follows in Part II. In addition, the original text of ��Invitation to join a discussion on self-reliance�� with the appended ��Declaration on Self-reliant Energy Analysis and Planning��, published in Volume VI No. 2 of ESD, is reprinted here in full to enable readers to appreciate better the responses contained here.
Toggweiler, J. R., A. Gnanadesikan, and S. Carson, 2003: Representation of the carbon cycle in box models and GCMs: 1. Solubility pump. Global Biogeochemical Cycles, 17(1), doi:10.1029/2001GB001401
[ Abstract ]
Bacastow [1996], Broecker et al. [1999], and Archer et al. [2000] have called attention recently to the fact that box models and general circulation models (GCMs) represent the thermal partitioning of CO₂ between the warm surface ocean and cold deep ocean in different ways. They attribute these differences to mixing and circulation effects in GCMs that are not resolved in box models. The message that emerges from these studies is that box models have overstated the importance of the ocean�s polar regions in the carbon cycle. A reduced role for the polar regions has major implications for the mechanisms put forth to explain glacial - interglacial changes in atmospheric CO₂. In parts 1 and 2 of this paper, a new analysis of the ocean�s carbon pumps is carried out to examine these findings. This paper, part 1, shows that unresolved mixing and circulation effects in box models are not the main reason for box model-GCM differences. The main factor is very different kinds of restrictions on gas exchange in polar areas. Polar outcrops in GCMs are much smaller than in box models, and they are assumed to be ice covered in an unrealistic way. This finding does not support a reduced role for the ocean�s polar regions in the cycling of organic carbon, the subject taken up in part 2.
Toggweiler, J. R., R. Murnane, S. Carson, A. Gnanadesikan, and Jorge Sarmiento, 2003: Representation of the carbon cycle in box models and GCMs: 2. Organic pump. Global Biogeochemical Cycles, 17(1), doi:10.1029/2001GB001841
[ Abstract ]
Box models of the ocean/atmosphere CO₂ system rely on mechanisms at polar outcrops to alter the strength of the ocean�s organic carbon pump. GCM-based carbon system models are reportedly less sensitive to the same processes. Here we separate the carbon pumps in a three-box model and the GCM-based Princeton Ocean Biogeochemistry Model to show how the organic pumps operate in the two kinds of models. The organic pumps are found to be quite different in two respects. Deep water in the three-box model is relatively well equilibrated with respect to the pCO₂ of the atmosphere while deep water in the GCM tends to be poorly equilibrated. This makes the organic pump inherently stronger in the GCM than in the three-box model. The second difference has to do with the role of polar nutrient utilization. The organic pump in the GCM is shown to have natural upper and lower limits that are set by the initial PO₄ concentrations in the deep water formed in the North Atlantic and Southern Ocean. The strength of the organic pump can swing between these limits in response to changes in deep-water formation that alter the mix of northern and southern deep water. Thus, unlike the situation in the three-box model, the organic pump in the GCM can become weaker or stronger without changes in polar nutrient utilization.
Watson, A. J., and J. C. Orr, 2003: Carbon dioxide fluxes in the global ocean. Ocean Biogeochemistry: A JGOFS Synthesis, Springer-Verlag Publishers, http://lgmacweb.env.uea.ac.uk/ajw/Watson_and_Orr_2002.pdf,
[ Abstract ]
Atmospheric carbon dioxide concentration is one of the key variables of the �Earth system� -- the web of interactions between the atmosphere, oceans, soils and living things that determines conditions at the Earth surface. Atmospheric CO₂ plays several roles in this system. For example, it is the carbon source for nearly all terrestrial green plants, and the source of carbonic acid to weather rocks. It is also an important greenhouse gas, with a central role to play in modulating the climate of the planet. During the five thousand years prior to the industrial revolution, we know (from measurements of air trapped in firn ice and ice cores) that atmospheric CO₂ varied globally by less than 10ppm from a concentration of 280ppm (Indermuhle et al. 1999). During the late Quaternary glaciations, the regular advance and retreat of the ice was accompanied by, and to some extent at least driven by (Li et al. 1998; Shackleton 2000), an oscillation in atmospheric CO₂ of about 80ppm. Evidence from the geologically recent past indicates therefore, that quite small changes in atmospheric carbon dioxide have big effects on planetary climate. Conversely, a stable concentration of CO₂ is necessary for a stable climate. By this reasoning, we can be fairly certain that human activities will have a major effect on the climate of the planet in the near future, given that we have raised CO₂ by 90ppm in the last 150 years and it is projected to double from the pre-industrial concentration during the coming century. This gives our investigations into sources and sinks of carbon dioxide a special urgency. For reasons that are made clear below, the oceans occupy a central role in the global carbon cycle and the processes influencing the concentration of CO₂ in the atmosphere. The JGOFS program represented the first sustained global effort to document the present state of the oceanic carbon cycle, and to test our understanding by comparing that state with the predictions of increasingly sophisticated numerical models. In the subsequent sections, we first discuss the role of the oceans in setting global atmospheric CO₂. JGOFS has made a major contribution to our estimate of the size of the present net flux of CO₂ from atmosphere to ocean, and we next review our estimates of this �sink� and how it may change in the future. This leads us to a discussion of the advances made in understanding the processes involved in setting that flux. Finally we summarize what we have learned during JGOFS and what the major topics of research are likely to be in the next 10 years.
Bender, Michael, 2002: Orbital tuning chronology for the Vostok climate record supported by trapped gas composition. Earth and Planetary Science Letters, 204(1-2), doi:10.1016/S0012-821X(02)00980-9 275-289
[ Abstract ]
We present data on the O₂/N₂ ratios of trapped gas samples for the entire length of the Vostok climate record. As in other cores, O₂/N₂ ratios in these samples are less than the atmospheric ratio, by a small and variable amount, because O₂ is selectively excluded during the gas trapping process, and because O₂ is also preferentially lost in poorly preserved core samples. Samples younger than 150ka have large and variable O₂ depletions. Samples older than 200 ka have O₂/N₂ ratios that replicate well and vary smoothly with depth. We plot O₂/N₂ ratios of well replicated samples older than 160ka, using a chronology derived by matching the δ¹⁸O of paleoatmospheric O₂ (δ¹⁸O_atm) to northern hemisphere June insolation. On this timescale, O₂/N₂ varies coherently with local (78�S) summertime insolation. Based on time series analysis of the O₂/N₂ record and the dynamics of snow metamorphism at the surface, we conclude that summertime insolation influences physical properties of ice grains that control the degree of O₂ exclusion during bubble closeoff. O₂/N₂ in Vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core. We show that the δ¹⁸O_atm chronology, supported by the coincidence of O₂/N₂ ratios with insolation, is also compatible with recent radiometric dating of corals from high sea stands. We further successfully test the N18Oatm tuning chronology by showing that it predicts a chronology for the GISP2 core which is essentially indistinguishable from the standard GISP2 chronology and, therefore, in excellent agreement with the radiometric chronology of Hulu Cave, China. An accurate chronology for the Vostok ice core is now in place.
Blunier, T., B. Barnett, Michael Bender, and M. B. Hendricks, 2002: Biological oxygen productivity during the last 60,000 years from triple oxygen isotope measurements. Global Biogeochemical Cycles, 16(3), doi:10.1029/2001GB001460
[ Abstract ]
The oxygen isotope signature of atmospheric O₂ is linked to the isotopic signature of seawater (H₂O) through photosynthesis and respiration. Fractionation during these processes is mass dependent, affecting δ ¹⁷O about half as much as δ ¹⁸O. An ��anomalous�� fractionation process, which changes δ ¹⁷O and δ ¹⁸O of O₂ about equally, takes place during isotope exchange between O₂ and CO₂ in the stratosphere. The relative rates of biologic O₂ production and stratospheric processing determine the relationship between δ ¹⁷O and δ ¹⁸O of O₂ in the atmosphere. Variations of this relationship thus allow us to estimate changes in the rate of mass-dependent O₂ production by photosynthesis versus the rate of O₂-CO₂ exchange in the stratosphere with about equal fractionations of δ ¹⁷O and δ ¹⁸O. In this study we reconstruct total oxygen productivity for the last glacial, the last glacial termination, and the early Holocene from the triple isotope composition of atmospheric oxygen trapped in ice cores.With a box model we estimate that total biogenic productivity was only ~76�83% of today for the glacial and was probably lower than today during the glacial-interglacial transition and the early Holocene. Depending on how reduced the oxygen flux from the land biosphere was during the glacial, the oxygen flux from the glacial ocean biosphere was 88�140% of its present value.
Brezeinski, M. A., C. J. Pride, V. M. Franck, Daniel Sigman, Jorge Sarmiento, K. Matsumoto, and N. Gruber, 2002: A switch from Si(OH)₄ to NO₃ depletion in the glacial Southern Ocean. Geophysical Research Letters, 29(12), doi:10.1029/2001GL014349 1564
[ Abstract ]
Phytoplankton in the Antarctic deplete silicic acid (Si(OH)₄) to a far greater extent than they do nitrate (NO₃). This pattern can be reversed by the addition of iron which dramatically lowers diatom Si(OH)₄: NO₃ uptake ratios. Higher iron supply during glacial times would thus drive the Antarctic towards NO₃ depletion with excess Si(OH)₄ remaining in surface waters. New δ³⁰SI and δ ¹⁵N records from Antarctic sediments confirm diminished Si(OH)₄ use and enhanced NO₃ depletion during the last three glaciations. The present low-Si(OH)₄ water is transported northward to at least the subtropics. We postulate that the glacial high-Si(OH)₄ water similarly may have been transported to the subtropics and beyond. This input of Si(OH)₄ may have caused diatoms to displace coccolithophores at low latitudes, weakening the carbonate pump and increasing the depth of organic matter remineralization. These effects may have lowered glacial atmospheric pCO₂ by as much as 60 ppm.
Carrillo, J. H., M. G. Hastings, Daniel Sigman, and B. J. Huebert, 2002: Atmospheric deposition of inorganic and organic nitrogen and base cations in Hawaii. Global Biogeochemical Cycles, 16(4), doi:10.1029/2002GB001892
[ Abstract ]
Atmospheric deposition of nitrogen (N) and base cations was measured for 5�7 years on the island of Hawaii and for 1.5 years on Kauai. On Hawaii, mean annual fluxes of K⁺, Mg²⁺, and Ca²⁺ were 15, 17, and 13 kg ha^-1 yr^-1, respectively. Fog interception was the largest deposition pathway. Sea salt contributed the majority of cations, although biomass burning and Asian dust were significant sources for some years. Total N deposition (inorganic and organic) averaged 17 kg N ha^-1 yr^-1. Fog interception was also the largest source of N, depositing 16 kg N ha^-1 yr^-1. Precipitation deposition was 1.0 and 0.2 kg N ha^-1 yr^-1, respectively on Hawaii and Kauai. Dry deposition on Hawaii was 0.1 kg N ha^-1 yr^-1. Organic N averaged 16 and 12% of total N in rain and fog, respectively. The δ¹⁵N values for NO₃-N are consistent with long-range transport of N from Asia in the spring/summer and from North America in the fall/winter as nonvolcanic sources. Atmospheric deposition on Hawaii may completely account for a previously identified soil N imbalance.
Casciotti, K. L., Daniel Sigman, M. G. Hastings, J. K. Böhlke, and A. Hilkert, 2002: Measurement of the oxygen isotopic composition of nitrate in seawater and freshwater using the denitrifier method. Analytical Chemistry, 74(19), doi:10.1021/ac020113w 4905-4912
[ Abstract ]
We report a novel method for measurement of the oxygen isotopic composition (¹⁸O/¹⁶O) of nitrate (NO₃ -) from both seawater and freshwater. The denitrifier method, based on the isotope ratio analysis of nitrous oxide generated from sample nitrate by cultured denitrifying bacteria, has been described elsewhere for its use in nitrogen isotope ratio (¹⁵N/¹⁴N) analysis of nitrate.1 Here, we address the additional issues associated with ¹⁸O/¹⁶O analysis of nitrate by this approach, which include (1) the oxygen isotopic difference between the nitrate sample and the N₂O analyte due to isotopic fractionation associated with the loss of oxygen atoms from nitrate and (2) the exchange of oxygen atoms with water during the conversion of nitrate to N₂O. Experiments with ¹⁸O labeled water indicate that water exchange contributes less than 10%, and frequently less than 3%, of the oxygen atoms in the N₂O product for Pseudomonas aureofaciens. In addition, both oxygen isotope fractionation and oxygen atom exchange are consistent within a given batch of analyses. The analysis of appropriate isotopic reference materials can thus be used to correct the measured ¹⁸O/¹⁶O ratios of samples for both effects. This is the first method tested for ¹⁸O/¹⁶O analysis of nitrate in seawater. Benefits of this method, relative to published freshwater methods, include higher sensitivity (tested down to 10 nmol and 1 μM NO₃ -), lack of interference by other solutes, and ease of sample preparation.
Chesson, P., Stephen W. Pacala, and C. Neuhauser, 2002: Environmental Niches and Ecosystem Functioning. The Functional Consequences of Biodiversity: Empirical Progress and Theoretical Extensions (MPB-33), Princeton University Press - Princeton, NJ, http://eebweb.arizona.edu/faculty/chesson/Peter/Reprints/2001_Environ, 213-245
[ Abstract ]
The idea that the response of an organism to components of its physical environment, as distinct from the availability of resources, is an important component of its niche. Differences between species in their environmental niches may promote their coexistence. The coexistence mechanism involved is the storage effect, augmented in the case of spatial variation by fitness density covariance. Environmental niches are temporal niches if they refer to temporally varying aspects of the physical environment, or spatial niches if they refer to spatially varying aspects of the physical environment, or spatio-temporal niches, if they refer simultaneously to variation in both space and time.
Dutay, J. C., J. L. Bullister, S. C. Doney, J. C. Orr, R. G. Najjar, K. Caldeira, J.-M. Campin, H. Drange, M. Follows, Y. Gao, and N. Gruber, et al., 2002: Evaluation of ocean model ventilation with CFC-11: comparison of 13 global ocean models. Ocean Modelling, 4(2), doi:10.1016/S1463-5003(01)00013-0 89-120
[ Abstract ]
We compared the 13 models participating in the Ocean Carbon Model Intercomparison Project (OCMIP) with regards to their skill in matching observed distributions of CFC-11. This analysis characterizes the abilities of these models to ventilate the ocean on timescales relevant for anthropogenic CO₂
Galloway, J. N., E. B. Cowling, S. P. Seitzinger, and Robert H. Socolow, March 2002: Reactive Nitrogen: Too Much of a Good Thing? Special Issue of Ambio:Optimizing Nitrogen Management in Food & Energy Productions, & Env Change, http://ambio.allenpress.com/archive/0044-7447/31/2/pdf/i0044-7447-31-2-60.pdf, 31(2), 60-63
[ Abstract ]
The 14^th element of the periodic table was named �nitrogene� by Jean Claude Chaptal in 1790 (1). Two centuries later, the role of nitrogen (N) in biogeochemical processes and its critical function as a necessary nutrient are well understood. We know that humans (and plants and animals) require N to survive. We know that the abundant supply of gaseous dinitrogen (N₂) in the atmosphere is in a chemical form that plants and animals cannot use directly. We know that only a few special microorganisms can transform (�fix�) atmospheric nitrogen into reactive nitrogen (Nr) (2) that plants and animals can use. We know that another small group of microorganisms can transform (denitrify) Nr back to N₂. Based on the constancy of the N₂O record, we know that N fixation and denitrification in pre-industrial times were approximately equal (3).
We also know that since the early 20th century, the amount of N fixed by unmanaged ecosystems has not been sufficient to meet human dietary needs. Fortunately, early in this period F. Haber and C. Bosch developed a process to tap the almost unlimited supply of nonreactive-N that exists in the atmosphere (1). This Haber-Bosch process made it possible to manufacture the Nr needed to meet the growing world food and fiber demand. Just as nitrogen is critical in human nutrition, it is also critical for all other plants and animals, from phytoplankton to elephants. The structure of whole ecosystems also is determined by Nr availability (4). As a result, Nr releases from food and energy production have the potential for significant unintended detrimental impacts on human health and both natural and managed ecosystems.
Globally, humans currently ingest ~ 20 Tg N yr^�1 in their food. All of this Nr enters the environment. The resulting environmental consequences are magnified substantially, however, because an additional ~ 100 Tg N yr^�1 that was involved in food production, but never entered human mouths, also was released to the environment. In addition to this total of ~ 120 Tg N yr^�1, another ~ 25 Tg N yr^�1 of Nr was created by fossil fuel combustion, and still another ~ 20 Tg N yr^�1 was created for other uses by the Haber-Bosch process, for a total of ~ 165 Tg N yr^�1. This amount is about twice the amount of reactive N created by biological nitrogen fixation (BNF) in natural terrestrial ecosystems (~ 90 Tg N y^�1) (5).
There is substantial regional variability in creation of Nr, its distribution, and its effects. Nr creation in Europe (6) and the United States (7) is dominated by both food and energy production; per-capita Nr creation rates are ~ 100 kg N capita^�1 yr^�1 and ~ 40 kg N capita�1 yr^�1, in North America and Europe, respectively. In Asia (8),
although total Nr creation is larger than in Europe and North America combined, the per capita Nr creation rate is much less: ~ 17 kg N capita^�1 yr^�1 (5). In the future, while Nr creation in Europe and North America might decrease, it most certainly will increase in Asia due to demands for food and energy by a growing human population with an increasing per capita use of nitrogen (8). Both the contrast between Nr production by humans and nature, and the potential environmental consequences of Nr production, have been recognized for more than 30 years (9). During the last 4 years especially, increased international attention has been focused on the complexities of human alteration of the N cycle and on how to optimize the production of food and energy while minimizing environmental consequences.
The First International Nitrogen Conference was held in March 1998 in The Netherlands. It documented the extent to which many of the world�s natural resources and environmental systems have been responding to Nr enrichment in recent decades (10). The Second International Nitrogen Conference was held in October 2001 in the USA and was attended by more than 400 participants from 30 countries on 6 continents. It provided a much-needed update on nitrogen science and policy 3 years after the First Conference. The Second Conference was designed to highlight policy relevant science. In addition, it provided an opportunity to focus on North America and to set the stage for a focus on Asia�the site of the Third International Nitrogen Conference in 2004.
The primary objectives of the Second Conference were to: � Increase scientific knowledge about Nr sources and effects on people and the environment;
� Stimulate communication among leaders involved in nitrogen production and consumption;
� Explore balanced strategies to increase food and energy production while decreasing impacts on people and the environment, thereby making progress toward the general theme of the Conference: �Optimizing Nitrogen Management in Food and Energy Production and Environmental Protection�.
The Second Conference produced 3 major products: i) A brief Conference Summary Statement (11); ii) the contributed papers of the Conference�130 peer-reviewed papers prepared by Conference participants and published in the The Scientific World in both electronic (12) and printed-book form (13); and iii) this AMBIO Special Issue on Reactive Nitrogen. This Issue is composed of 17 papers derived from the plenary presentations at the Conference. Most of the authors met for 2.5 days at the Erik Jonsson Center of the National Academy of Sciences in Woods Hole, Massachusetts in April 2001 to plan the integration of their diverse topics. Most papers were then distributed among the plenary authors prior to the Conference in October 2001. After the Conference, the papers were still further revised and improved in response to comments from other plenary authors, anonymous reviewers, and from us as editors.
The remainder of this introductory paper summarizes scientific highlights and recommendations for decision-makers derived from the Second Conference. As outlined in the Table of Contents for this AMBIO Special Issue on Reactive Nitrogen, these 17 plenary papers provide outstanding summaries of Nr science and policy.
Gnanadesikan, A., R. D. Slater, N. Gruber, and Jorge Sarmiento, 2002: Oceanic vertical exchange and new production: A comparison between models and observations. Deep Sea Research II, 49(1-3), doi:10.1016/S0967-0645(01)00107-2 363-401
[ Abstract ]
This paper explores the relationship between large-scale vertical exchange and the cycling of biologically active nutrients within the ocean. It considers how the parameterization of vertical and lateral mixing effects estimates of newproducti on (defined as the net uptake of phosphate). A baseline case is run with low vertical mixing in the pycnocline and a relatively lowlate ral diffusion coefficient. The magnitude of the diapycnal diffusion coefficient is then increased within the pycnocline, within the pycnocline of the Southern Ocean, and in the top 50 m; while the lateral diffusion coefficient is increased throughout the ocean. It is shown that it is possible to change lateral and vertical diffusion coefficients so as to preserve the structure of the pycnocline while changing the pathways of vertical exchange and hence the cycling of nutrients. Comparisons between the different models reveal that new production is very sensitive to the level of vertical mixing within the pycnocline, but only weakly sensitive to the level of lateral and upper ocean diffusion. The results are compared with two estimates of new production based on ocean color and the annual cycle of nutrients. On a global scale, the observational estimates are most consistent with the circulation produced with a low diffusion coefficient within the pycnocline, resulting in a new production of around 10 GtC yr¹: On a regional level, however, large differences appear between observational and model based estimates. In the tropics, the models yield systematically higher levels of new production than the observational estimates. Evidence from the Eastern Equatorial Pacific suggests that this is due to both biases in the data used to generate the observational estimates and problems with the models. In the North Atlantic, the observational estimates vary more than the models, due in part to the methodology by which the nutrient-based climatology is constructed. In the North Pacific, the modeled values of new production are all much lower than the observational estimates, probably as a result of the failure to form intermediate water with the right properties. The results demonstrate the potential usefulness of new production for evaluating circulation models.
Gruber, N., and Jorge Sarmiento, 2002: Large �scale biogeochemical-physical interactions in elemental cycles. The Sea, John Wiley & Sons, Inc., 12, 337-399
[ Abstract ]
Introduction Why is the distribution of most chemicals not uniform within the ocean? In the absence of sources and sinks the effect of ocean circulation and mixing would be to smooth the distribution of chemicals. An important reason for non-uniformity is the increase in concentration that occurs in regions of evaporation, and the reduction in concentration that occurs in regions of rainfall or river input at the ocean atmosphere interface. Evaporation, precipitation, and river input lead to concentration ranges usually well below 10% as evidenced in the oceanic variability of salinity. However, as Figure1 shows, many chemicals have concentration ranges much greater than this. The concentration of inorganic nitrogen, for example, is more than five times smaller near the surface compared to the deep ocean. Dissolved inorganic carbon shows a surface depletion that is also substantially larger than the 10% variation that could be induced by freshwater fluxes. The primary mechanism that drives such large concentration gradients is the use of dissolved inorganic chemicals by living organisms for formation of organic matter and inorganic solids. Photosynthetic organisms use the energy from light in the upper part of the ocean to produce both particulate and dissolved organic matter and a wide range of inorganic solids as well. These "biogenic" materials are often transported long distances before being converted back to dissolved inorganic chemicals by processes such as "remineralization" and dissolution. The largest such transports are vertical, giving rise to greatly reduced concentrations in the surface ocean, and enhanced concentrations in the abyss. A few chemicals, the most important being oxygen, are affected by these processes in the opposite direction. They are released during photosynthesis and consumed during remineralization. The wide range of biological and associated processes that affect such chemicals are referred to as "biogeochemical" processes. The view that therefore emerges with regard to the large scale distribution of chemicals in the ocean is one where biogeochemical processes are constantly creating spatial and temporal gradients in the chemicals, whereas ocean circulation and mixing are in general attempting to homogenize these gradients. The resulting distribution of the chemicals in the ocean can thus be understood as the result of a complex interplay between biogeochemical cycles and ocean physics. These large scale biogeochemical/physical interactions are the focus of this chapter. In particular, we are interested in determining the relative roles of the various ``gradient makers'' in creating the large-scale distribution of chemicals in the ocean. We will focus our discussion on the two most important biogeochemical elements, carbon and nitrogen. We will include the cycling of phosphorus and oxygen since they allow us to gain much additional information about carbon and nitrogen.
Gurney, K. R., R. M. Law, A. S. Denning, P. J. Rayner, D. Baker, P. Bousquet, L. Bruhwiler, Y.-H. Chen, P. Ciais, S. Fan, I. Y. Fung, and M. N. Gloor, et al., 2002: Towards robust regional estimates of CO₂ sources and sinks using atmospheric transport models. Nature, 415, doi:10.1038/415626a 626-630
[ Abstract ]
Information about regional carbon sources and sinks can be derived from variations in observed atmospheric CO₂ concentrations via inverse modeling with atmospheric tracer transport models. A consensus has not yet been reached regarding the size and distribution of regional carbon fluxes obtained using this approach, partly owing to the use of several different atmospheric transport models. Here we report estimates of surface atmosphere CO₂ fluxes from an intercomparison of atmospheric CO₂ inversion models (the TransCom 3 project), which includes 16transportmodelsandmodelvariants. We find an uptake of CO₂ in the southern extra tropical ocean less than that estimated from ocean measurements, a result that is not sensitive to transport models or methodological approaches. We also find a northern land carbon sink that is distributed relatively evenly among the continents of the Northern Hemisphere, but these results show some sensitivity to transport differences among models, especially in how they respond to seasonal terrestrial exchange of CO₂. Overall, carbon fluxes integrated over latitudinal zones are strongly constrained by observations in the middle to high latitudes. Further significant constraints to our understanding of regional carbon fluxes will therefore require improvements in transport models and expansion of the CO₂ observation network within the tropics. We estimate annual average fluxes for the 1992-96 period using each transport model and a common inversion set-up (see Methods). Methodological choices for this 'control' inversion have been selected on the basis of knowledge gained from a wide range of sensitivity tests (to be reported elsewhere). Performing the inversion with multiple transport models gives mean estimated fluxes that are relatively insensitive to reasonable variations in the set-up-and estimated uncertainties that represent a more complete estimate of the true uncertainty. The maximum number of Southern 0cean fluxes had been noted a decade ago. 0ur sensitivity tests find that the near-uniformity of observed concentration in the Southern Hemisphere and the small uncertainty associated with those measurements make this result robust to the choice of observing network, prior flux estimates, global ocean constraint, and transport (see Fig 2 in Supplementary Information). The discrepancy also cannot be explained by a systematic bias in transport models, as the north-south transport has been investigated in a recent intercomparison where successful simulations of the observed meridional gradient in SF₆ suggested reasonable veracity in gross interhemispheric transport. 0ne possible reconciliation between the pCO₂ database and the inverse result presented here is suggested by recent ocean measurements taken during January and August 2000 in the Indian Ocean.
Hixon, M. A., Stephen W. Pacala, and S. A. Sandin, 2002: Population regulation: historical context and contemporary challenges of open vs. closed systems. Ecology, 83(6), doi:10.1890/0012-9658(2002)083[1490:PRHCAC]2.0.CO;2 1490-1508
[ Abstract ]
By definition, a population is regulated if it persists for many generations with fluctuations bounded above zero with high probability. Regulation thus requires density- dependent negative feedback whereby the population has a propensity to increase when small and decrease when large. Ultimately, extinction occurs due to regulating mechanisms becoming weaker than various disruptive events and stochastic variation. Population regulation is one of the foundational concepts of ecology, yet this paradigm has often been challenged, during the first half of the 20th century when the concept was not clearly defined, and more recently by some who study demographically open populations. The history of ecology reveals that earlier manifestations of the concept focused mostly on competition as the mechanism of population regulation. Because competition is often not evident in nature, it was sometimes concluded that population regulation was therefore also absent. However, predation in the broadest sense can also cause density dependence. By the 1950s, the idea that demographic density dependence was essential (but not sufficient) for population regulation was well established, and since then, challenges to the general concept have been short lived. However, some now believe that metapopulations composed of demographically open local populations can persist without density dependence. In particular, some recent manifestations of the Recruitment Limitation Hypothesis all but preclude the possibility of regulation. The theory of locally open populations indicates that persistence always relies on direct demographic density dependence at some spatial and temporal scale, even in models reportedly demonstrating the contrary. There is also increasing empirical evidence, especially in marine systems where competition for space is not self evident, that local density dependence is more pervasive than previously assumed and is often caused by predation. However, there are currently insufficient data to test unequivocally whether or not any persistent metapopulation is regulated. The challenge for more complete understanding of regulation of metapopulations lies in combined empirical and theoretical studies that bridge the gap between smaller scale field experiments and larger scale phenomena that can presently be explored solely by theory.
Iglesias-Rodriguez, M., R. A. Armstrong, R. A. Feely, R. Hood, J. Kleypas, J. D. Milliman, C. L. Sabine, and Jorge Sarmiento, 2002: The Marine Calcium Carbonate Budget in a Changing Ocean. EOS Transactions, 83(34), 374-375
[ Abstract ]
Many of the uncertainties in diagnostic and prognostic marine carbon cycle models arise from an imperfect understanding of processes that control formation and dissolution of calcium carbonate (CaCO₃). On the production side of the equation, factors that control the abundances of calcifying phytoplankton (coccolithophorids) or zooplankton (foraminifera and pteropods) are largely unknown. On the dissolution side, changes in the depth of CaCO₃ saturation horizons (for both calcite and aragonite) may produce large-scale changes in dissolution of shelf and slope sediments and reefs, with potentially significant implications for atmospheric carbon dioxide concentration and climate change, and for coralline organisms themselves. In this article we summarize our present understanding of the marine CaCO₃ cycle, including information presented at the 2001 US JGOFS Workshop on Marine Calcification (http://usjgofs.whoi.edu/mzweb/caco3_rpt.html), and highlight gaps in our understanding of key mechanisms that may affect future changes in the CaCO₃ budget.
Karl, D., A. Michaels, B. Bergman, D. Capone, E. Carpenter, R. M. Letelier, F. Lipschultz, H. Paerl, Daniel Sigman, and L. Stal, 2002: Dinitrogen fixation in the world�s oceans. Biogeochemistry, 57/58, doi:10.1023/A:1015798105851 47-98
[ Abstract ]
The surface water of the marine environment has traditionally been viewed as a nitrogen (N) limited habitat, and this has guided the development of conceptual biogeochemical models focusing largely on the reservoir of nitrate as the critical source of N to sustain primary productivity. However, selected groups of Bacteria, including cyanobacteria, and Archaea can utilize dinitrogen (N₂) as an alternative N source. In the marine environment, these microorganisms can have profound effects on net community production processes and can impact the coupling of C-N-P cycles as well as the net oceanic sequestration of atmospheric carbon dioxide. As one component of an integrated 'Nitrogen Transport and Transformations' project, we have begun to re-assess our understanding of (1) the biotic sources and rates of N₂ fixation in the world's oceans, (2) the major controls on rates of oceanic N₂ fixation, (3) the significance of this N_x fixation for the global carbon cycle and (4) the role of human activities in the alteration of oceanic N₂ fixation. Preliminary results indicate that rates of N₂ fixation, especially in subtropical and tropical open ocean habitats, have a major role in the global marine N budget. Iron (Fe) bioavailability appears to be an important control and is, therefore, critical in extrapolation to global rates of N₂ fixation. Anthropogenic perturbations may alter N₂ fixation in coastal environments through habitat destruction and eutrophication, and open ocean N₂ fixation may be enhanced by warming and increased stratification of the upper water column. Global anthropogenic and climatic changes may also affect N₂ fixation rates, for example by altering dust inputs (i.e. Fe) or by expansion of subtropical boundaries. Some recent estimates of global ocean N₂ fixation are in the range of 100-200 Tg N (1-2 x 10¹⁴ g N) yr^-1, but have large uncertainties. These estimates are nearly an order of magnitude greater than historical, pre-1980 estimates, but approach modem estimates of oceanic denitrification.
Kinzig, A. P., Stephen W. Pacala, and G. D. Tilman, 2002: Looking Back, Peering Forward (editors. The Functional Consequences of Biodiversity: Experimental Progress and Theoretical Extensions, Princeton, NJ, Princeton University Press, 314-329
[ Abstract ]
Does biodiversity influence how ecosystems function? Might diversity loss affect the ability of ecosystems to deliver services of benefit to humankind? Ecosystems provide food, fuel, fiber, and drinkable water, regulate local and regional climate, and recycle needed nutrients, among other things. An ecosystem's ability to sustain functioning may depend on the number of species residing in the ecosystem--its biological diversity--but this has been a controversial hypothesis. There are many unanswered questions about how and why changes in biodiversity could alter ecosystem functioning. This volume, written by top researchers, synthesizes empirical studies on the relationship between biodiversity and ecosystem functioning and extends that knowledge using a novel and coordinated set of models and theoretical approaches. These experimental and theoretical analyses demonstrate that functioning usually increases with biodiversity, but also reveals when and under what circumstances other relationships between biodiversity and ecosystem functioning might occur. It also accounts for apparent changes in diversity-functioning relationships that emerge over time in disturbed ecosystems, thereby addressing a major controversy in the field. The volume concludes with a blueprint for moving beyond small-scale studies to regional ones--a move of enormous significance for policy and conservation but one that will entail tackling some of the most fundamental challenges in ecology. In addition to the editors, the contributors are Juan Armesto, Claudia Neuhauser, Andy Hector, Clarence Lehman, Peter Kareiva, Sharon Lawler, Peter Chesson, Teri Balser, Mary K. Firestone, Robert Holt, Michel Loreau, Johannes Knops, David Wedin, Peter Reich, Shahid Naeem, Bernhard Schmid, Jasmin Joshi, and Felix Schl�pfer.
Kreutz, Thomas, Robert H. Williams, Robert H. Socolow, P. Chiesa, and G. G. Lozza, September 2002: Production of Hydrogen and Electricity from Coal with CO₂ Capture. Proceedings of the 6th International Conference on Greenhouse Gas Control Technologies (GHGT-6), http://www.princeton.edu/pei/energy/publications/texts/Kreutz_Kyoto_02.pdf,
[ Abstract ]
This paper summarizes a series of studies examining the prospective performance and cost of facilities that convert coal to H₂, co-product electricity and a stream of concentrated CO₂ (for sequestration). Synthe-sis gas is produced via oxygen-blown, entrained flow coal gasification, quench cooled and shifted to (pri-marily) H₂ and CO₂ via sulfur-tolerant water-gas shift (WGS) reactors. Our focus is on separating H₂ from the syngas and processing the carbon-bearing raffinate/purge gas to produce electricity and CO₂. We explore the use of novel inorganic membrane reactors for H₂ separation and compare their performance and cost with conventional gas separation technologies: CO₂ capture via solvent absorption followed by H₂ purification using pressure swing adsorption (PSA). This work highlights potential economic benefits of high system pressure, low H₂ purity, and co-sequestering CO₂ with sulfur-bearing waste gases, H₂S and SO₂.
Matsumoto, K., Jorge Sarmiento, and M. A. Brezeinski, 2002: Silicic acid leakage from the Southern Ocean: A possible explanation for glacial atmospheric pCO₂. Global Biogeochemical Cycles, 16(3), doi:10.1029/2001GB001442
[ Abstract ]
Using a simple box model, we investigate the effects of a reduced Si:N uptake ratio by Antarctic phytoplankton on the marine silica cycle and atmospheric pCO₂. Recent incubation experiments demonstrate such a phenomenon in diatoms when iron is added [Hutchins and Bruland, 1998; Takeda, 1998; Franck et al., 2000]. The Southern Ocean may have supported diatoms with reduced Si:N uptake ratios compared to today during the dustier glacial times [Petit et al., 1999]. A similar reduction in the uptake ratio may be realized with an increased production of nondiatom phytoplankton such as Phaeocystis. Our model shows that reduced Si:N export ratios in the Southern Ocean create excess silicic acid, which may then be leaked out to lower latitudes. Any significant consumption of the excess silicic acid by diatoms that leads to an enhancement in their growth at the expense of coccolithophorids diminishes CaCO₃production and therefore diminishes the carbonate pump. In our box model the combination of a reduced carbonate pump and an open system carbonate compensation draw down steady state atmospheric CO₂ from the interglacial 277 to 230�242 ppm, depending on where the excess silicic acid is consumed. By comparison, the atmospheric pCO₂ sensitivity of general circulation models to carbonate pump forcing is �3.5�fold greater, which, combined with carbonate compensation, can account for peak glacial atmospheric pCO₂. We discuss the importance of the initial rain ratio of CaCO₃ to organic carbon on atmospheric pCO₂ and relevant sedimentary records that support and constrain this ��silicic acid leakage�� scenario.
O'Neill, B., and Michael Oppenheimer, 2002: Climate change - Dangerous climate impacts and the Kyoto protocol. Science, 296, doi:10.1126/science.1071238 1971-1972
[ Abstract ]
Defining a long-term goal for climate change policy remains a critical international challenge. Article 2 of the UN Framework Convention on Climate Change defines the long-term objective of that agreement as stabilization of greenhouse gas concentrations at a level that avoids �dangerous anthropogenic interference� with the climate system. �Dangerous interference� can be viewed from a variety of perspectives, and the choice will ultimately involve a mixture of scientific, economic, political, ethical, and cultural considerations, among others (1). In addition, the links among emissions, greenhouse gas concentrations, climate change, and impacts are uncertain. Furthermore, what might be considered dangerous could change over time. However, both proponents and detractors of the Kyoto Protocol, which was designed as an initial step to implement the Framework Convention, have begun to demand a definition of long-term objectives. For example, on 11 June 2001, U.S. President George W. Bush stated that the emissions targets embodied in the Kyoto Protocol �were arbitrary and not based upon science� and �no one can say with any certainty what constitutes a dangerous level of warming, and therefore what level must be avoided.� Here, we propose several plausible interpretations of dangerous interference in terms of particular environmental outcomes (2) and examine the consistency between the Kyoto Protocol and emissions changes over time that would avoid these outcomes. Although the emissions limits required by the Kyoto Protocol would reduce warming only marginally (3), we show that the accord provides a first step that may be necessary for avoiding dangerous interference.
Oppenheimer, Michael, 2002: Book Review - Jeremy Leffett, The Carbon War: Global Warming and the End of the Oil Era. Climatic Change, 54(4), doi:10.1023/A:1016135402292 497-505
[ Abstract ]
Jeremy Leggett: 2000, The Carbon War: Global Warming and the End of the Oil Era, Penguin Books, 342 pp., ISBN 0-14-028494-X
With the U.S. government rejecting further consideration of the Kyoto Protocol and the EU and other countries moving toward its ratification, it is far too early to write the definitive political history of the global warming problem. The public policy issue named Global Warming or Climate Change has many moving parts, with each at a different stage of development. Much is known about the geophysical and technological aspects of the issue and rather less about its biological and economic implications. Tomes have been written on each aspect, most notably the reports of the Intergovernmental Panel on Climate Change (IPCC).
However, on the political and diplomatic aspects of the issue, the literature, as voluminous as it is, leaves much to be desired. There are lots of questions and not enough credible answers. Is the UN Framework Convention on Climate Change a noble but ultimately toothless statement of purpose or a set of visionary principles? Is the Kyoto Protocol the first step on a long road or a time-consuming detour? Are the European countries heroes or hypocrites for savaging the U.S.�s demurral on Kyoto? What about the myriad technologies, policies, and mechanisms for abating greenhouse gases and their consequences, including emission taxes, emission trading, solar energy, nuclear energy, energy efficiency, sinks, geo-engineering, natural gas, and so on? What will work outside the think tanks in the real world of politics and people? Most important of all, when, if ever, will the developing countries agree to emissions limitation?
Have you been hammering your head against the wall on one side of this issue or another for longer than you care to remember? Have you had enough of the details? Do you want to relax with a good book? Allow me to recommend The Carbon War by Jeremy Leggett. Dr. Leggett, former oil geologist and former Greenpeace campaigner, is currently a solar energy entrepreneur. Leggett had a bright idea. By proselytizing insurance companies and other firms in the financial sector about the damage to insured property in a progressively less-predictable and potentially more-violent climate, he would try to convince them to lobby in favor of greenhouse gas reductions while altering their investment portfolios to favor solar energy. The Carbon War is a diary of those efforts. As in most interesting stories, there
Pacala, Stephen W., and A. P. Kinzig, 2002: Introduction to Theory and the Common Ecosystem Model. The Functional Consequences of Biodiversity: Experimental Progress and Theoretical Extensions, Princeton, NJ, Princeton University Press, 169-174
[ Abstract ]
Does biodiversity influence how ecosystems function? Might diversity loss affect the ability of ecosystems to deliver services of benefit to humankind? Ecosystems provide food, fuel, fiber, and drinkable water, regulate local and regional climate, and recycle needed nutrients, among other things. An ecosyste's ability to sustain functioning may depend on the number of species residing in the ecosystem--its biological diversity--but this has been a controversial hypothesis. There are many unanswered questions about how and why changes in biodiversity could alter ecosystem functioning. This volume, written by top researchers, synthesizes empirical studies on the relationship between biodiversity and ecosystem functioning and extends that knowledge using a novel and coordinated set of models and theoretical approaches. These experimental and theoretical analyses demonstrate that functioning usually increases with biodiversity, but also reveals when and under what circumstances other relationships between biodiversity and ecosystem functioning might occur. It also accounts for apparent changes in diversity-functioning relationships that emerge over time in disturbed ecosystems, thereby addressing a major controversy in the field. The volume concludes with a blueprint for moving beyond small-scale studies to regional ones--a move of enormous significance for policy and conservation but one that will entail tackling some of the most fundamental challenges in ecology. In addition to the editors, the contributors are Juan Armesto, Claudia Neuhauser, Andy Hector, Clarence Lehman, Peter Kareiva, Sharon Lawler, Peter Chesson, Teri Balser, Mary K. Firestone, Robert Holt, Michel Loreau, Johannes Knops, David Wedin, Peter Reich, Shahid Naeem, Bernhard Schmid, Jasmin Joshi, and Felix Schl�pfer.
Pacala, Stephen W., A. P. Kinzig, and G. D. Tilman, 2002: The Transition from Sampling to Complementarity. The Functional Consequences of Biodiversity: Experimental Progress and Theoretical Extensions, Princeton, NJ, Princeton University Press, 151-166
[ Abstract ]
Does biodiversity influence how ecosystems function? Might diversity loss affect the ability of ecosystems to deliver services of benefit to humankind? Ecosystems provide food, fuel, fiber, and drinkable water, regulate local and regional climate, and recycle needed nutrients, among other things. An ecosyste's ability to sustain functioning may depend on the number of species residing in the ecosystem--its biological diversity--but this has been a controversial hypothesis. There are many unanswered questions about how and why changes in biodiversity could alter ecosystem functioning. This volume, written by top researchers, synthesizes empirical studies on the relationship between biodiversity and ecosystem functioning and extends that knowledge using a novel and coordinated set of models and theoretical approaches. These experimental and theoretical analyses demonstrate that functioning usually increases with biodiversity, but also reveals when and under what circumstances other relationships between biodiversity and ecosystem functioning might occur. It also accounts for apparent changes in diversity-functioning relationships that emerge over time in disturbed ecosystems, thereby addressing a major controversy in the field. The volume concludes with a blueprint for moving beyond small-scale studies to regional ones--a move of enormous significance for policy and conservation but one that will entail tackling some of the most fundamental challenges in ecology. In addition to the editors, the contributors are Juan Armesto, Claudia Neuhauser, Andy Hector, Clarence Lehman, Peter Kareiva, Sharon Lawler, Peter Chesson, Teri Balser, Mary K. Firestone, Robert Holt, Michel Loreau, Johannes Knops, David Wedin, Peter Reich, Shahid Naeem, Bernhard Schmid, Jasmin Joshi, and Felix Schl�pfer.
Pacala, Stephen W., October 2002: Global Constraints on Reservoir Leakage. Proceedings of the 6th International Conference on Greenhouse Gas Control Technologies (GHGT-6), 267-272
[ Abstract ]
A crucial unresolved problem about geological sequestration is that some receptor reservoirs will leak stored CO₂. At local scales, leaks might endanger shallower drinking water supplies or public health. At global scales, leaks might be large enough to make sequestration ineffective. This paper focuses on the global-scale problem and uses models of carbon storage reservoirs and natural carbon sinks to calculate constraints on reservoir leakage. It assumes fossil fuel consumption at a level that would that would lead to an atmospheric CO₂ concentration of 750 ppm and then calculates the sequestration and leakage limits that would reduce the maximum concentration to 450 or 550 ppm. The surprising result is that leakage limits are much less severe than expected because of heterogeneity among reservoirs. In some cases, the reduction from 750 to 450 ppm would be possible even with a mean leakage rate of 1% per year or more. The results imply that economic considerations or local risks are likely to constrain allowable leakage rates more tightly than impacts of leakage on global atmospheric CO₂.
Pantoja, S., D. J. Repeta, J. P. Sachs, and Daniel Sigman, 2002: Stable isotope constraints on the nitrogen cycle of the Mediterranean Sea water column. Deep Sea Research I, 49(9), doi:10.1016/S0967-0637(02)00066-3 1609-1621
[ Abstract ]
We used the nitrogen isotope ratio of algae, suspended particles and nitrate in the water column to track spatial variations in the marine nitrogen cycle in the Mediterranean Sea. Surface PON (5�74 m) was more depleted in ¹⁵N in the eastern basin (-0.3 � 0.5%) than in the western basin (+2.4 � 1.4%), suggesting that nitrogen supplied by biological N₂ fixation may be an important source of new nitrogen in the eastern basin, where preformed nitrate from the Atlantic Ocean could have been depleted during its transit eastward. The δ¹⁵N of nitrate in the deep Mediterranean (~ 3%in the western-most Mediterranean and decreasing toward the east) is significantly lower than nitrate at similar depths from the North Atlantic (4.8�5%), also suggesting an important role for N2 fixation. The eastward decrease in the δ¹⁵N of surface PON is greater than the eastward decrease in the δ¹⁵N of the subsurface nitrate, implying that the amount of N2 fixation in the eastern Mediterranean is great enough to cause a major divergence in the δ¹⁵N of phytoplankton biomass from the δ¹⁵N of the nitrate upwelled from below. Variations in productivity associated with frontal processes, including shoaling of the nitracline, did not lead to detectable variations in the δ¹⁵N of PON. This indicates that no differential fertilization or productivity gradient occurred in the Almerian/Oran area. Our results are consistent with a lack of gradient in chlorophyll-a (chl-a) and nitrate concentration in the Alboran Sea. ¹⁵N enrichment in particles below 500m depth was detected in the Alboran Sea with respect to surface PON, reaching an average value of +7.470.7%. The δ¹⁵N in sinking particles caught at 100m depth (4.9�5.6%) was intermediate between suspended surface and suspended deep particles. We found a consistent difference in the isotopic composition of nitrogen in PON compared with that of chlorophyll (Δδ¹⁵N[PON-chlorin]=+6.4 � 1.4%) in the surface, similar to the offset reported earlier in cultures for cellular N and chl- a. This indicates that δ¹⁵N of phytoplankton biomass was retained in surface PON, and that alteration of the isotopic signal of PON at depth was due to heterotrophic activity.
Peylin, P., D. Baker, Jorge Sarmiento, P. Ciais, and P. Bousquet, 2002: Influence of transport uncertainty on annual mean and seasonal inversions of atmospheric CO₂ data. Journal of Geophysical Research, 107(D19), doi:10.1029/2001JD000857
[ Abstract ]
Inversion methods are often used to estimate surface CO₂ fluxes from atmospheric CO₂ concentration measurements, given an atmospheric transport model to relate the two. The published estimates disagree strongly on the location of the main sources and sinks, however. Are these differences due to the different time spans considered, or are they artifacts of the method and data used? Here we assess the uncertainty in such estimates due to the choice of time discretization of the measurements and fluxes, the spatial resolution of the fluxes, and the transport model. A suite of 27 Bayesian least squares inversions has been run, given by varying the number of flux regions solved for (7, 12, and 17), the time discretization (annual/annual, annual/monthly, and monthly/monthly for the fluxes/data), and the transport model (TM2, TM3, and GCTM), while holding all other inversion details constant. The estimated fluxes from this ensemble of inversions for the land + ocean sum are stable over large zonal bands, but the spread in the results increases when considering the longitudinal flux distribution inside these bands. On average for 1990� 1994 the inversions place a large CO₂ uptake north of 30°N (3.2 � 0.3 GtC yr^-1), mostly over the land regions, with more in Eurasia than North America. The ocean fluxes are generally smaller than given by Takahashi et al. [1999], especially south of 15°S and in the global total, where they are less than half as large. A small uptake is found for the tropical land regions, suggesting that growth more than compensates for deforestation there. The results for the different transport models are consistent with their known mixing properties; the longitudinal pattern of their land biosphere rectifier, in particular, strongly influences the regional partitioning of the flux in the north. While differences between the transport models contribute significantly to the spread of the results, an equivalent or even larger spread is due to the time discretization method used: Solving for annual mean fluxes with monthly mean measurements tended to give spurious land/ocean flux partition in the north.We suggest then that this time discretization method be avoided. Overall, the uncertainty quoted for the estimated fluxes should include not only the random error calculated by the inversion equations but also all the systematic errors in the problem, such as those addressed in this study.
Sarmiento, Jorge, J. P. Dunne, A. Gnanadesikan, R. M. Key, K. Matsumoto, and R. D. Slater, 2002: A new estimate of the CaCO₃ to organic carbon export ratio. Global Biogeochemical Cycles, 16(4), doi:10.1029/2002GB001919
[ Abstract ]
We use an ocean biogeochemical-transport box model of the top 100 m of the water column to estimate the CaCO₃ to organic carbon export ratio from observations of the vertical gradients of potential alkalinity and nitrate. We find a global average molar export ratio of 0.06 � 0.03. This is substantially smaller than earlier estimates of 0.25 on which a majority of ocean biogeochemical models had based their parameterization of CaCO₃ production. Contrary to the pattern of coccolithophore blooms determined from satellite observations, which show high latitude predominance, we find maximum export ratios in the equatorial region and generally smaller ratios in the subtropical and subpolar gyres. Our results suggest a dominant contribution to global calcification by low-latitude nonbloom forming coccolithophores or other organisms such as foraminifera and pteropods.
Sarmiento, Jorge, and N. Gruber, 2002: Sinks for anthropogenic carbon. Physics Today, http://www.gfdl.noaa.gov/bibliography/related_files/jls0202.pdf, 55, 30-36
[ Abstract ]
The ocean�s biological pump strips nutrients out of the surface waters and exports them into the thermocline and deep waters. If there were no return path of nutrients from deep waters, the biological pump would eventually deplete the surface waters and thermocline of nutrients; surface biological productivity would plummet. Here we make use of the combined distributions of silicic acid and nitrate to trace the main nutrient return path from deep waters by upwelling in the Southern Ocean1 and subsequent entrainment into subantarctic mode water. We show that the subantarctic mode water, which spreads throughout the entire Southern Hemisphere 2,3 and North Atlantic Ocean3, is the main source of nutrients for the thermocline. We also find that an additional return path exists in the northwest corner of the Pacific Ocean, where enhanced vertical mixing, perhaps driven by tides4, brings abyssal nutrients to the surface and supplies them to the thermocline of the North Pacific. Our analysis has important implications for our understanding of large-scale controls on the nature and magnitude of low-latitude biological productivity and its sensitivity to climate change.
Socolow, Robert H., 2002: The Century-Long Challenge of Fossil-Carbon Sequestration. U.S. Policy on Climate Change: What Next?, The Aspen Institute, Washington, D.C., http://www.princeton.edu/mae/people/faculty/socolow/century-long.pdf, 97-107
[ Abstract ]
The time scale of the Greenhouse problem is a century. This is an unfamiliar time scale for political action.
The Greenhouse problem arises if the global energy system is dominated by fossil fuels throughout this century. Such dominance is likely. But there is a fossil-fuel-based solution. It is conceivable that most of the carbon in the next hundred years of fossil fuels can be prevented from reaching (can be "sequestered" from) the atmosphere.
Fossil-carbon sequestration is conceptually entirely different from biological-carbon sequestration, yet, unfortunately, both kinds of sequestration are usually called, simply, "sequestration." Biological carbon sequestration removes carbon from the atmosphere.
The politics of fossil-carbon sequestration are unlike the politics of carbon management strategies designed to bring the fossil fuel era to a rapid close. The fossil fuel industries are willing participants, and they are showing leadership. So are many countries and portions of countries rich in fossil fuel resources The result should be new coalitions supportive of policies intended to mitigate climate change.
Tortell, P. D., G. R. Di Tullio, Daniel Sigman, and Francois Morel, 2002: CO₂ effects on taxonomic composition and nutrient utilization in an Equatorial Pacific phytoplankton assemblage. Marine Ecology Progress Series, 236, doi:10.3354/meps236037 37-43
[ Abstract ]
We report the results of a field incubation experiment demonstrating a substantial shift in the taxonomic composition of Equatorial Pacific phytoplankton assemblages exposed to CO₂ levels of 150 and 750 ppm (dissolved CO₂ ~3 to 25 μM). By the end of the experiment, the phytoplankton community in all samples was dominated by diatoms and Phaeocystis sp. However, the relative abundance of these phytoplankton taxa differed significantly between CO₂ treatments. Taxonomic pigment analysis and direct microscopic examination of samples revealed that the abundance of diatoms decreased by ~50% at low CO₂ relative to high CO₂, while the abundance of Phaeocystis sp. increased by ~60% at low CO₂. This CO₂-dependent shift was associated with a significant change in nutrient utilization, with higher ratios of nitrate:silicate (N:Si) and nitrate:phosphate (N:P) consumption by phytoplankton in the low CO₂ treatment. Despite the significant changes in taxonomic composition and nutrient consumption ratios, total biomass and primary productivity did not differ significantly between the CO₂ treatments. Our results suggest that CO₂ concentrations could potentially influence competition among marine phytoplankton taxa and affect oceanic nutrient cycling.
Deutsch, C., N. Gruber, R. M. Key, and Jorge Sarmiento, 2001: Denitrification and N₂ fixation in the Pacific Ocean. Global Biogeochemical Cycles, http://www.agu.org/journals/gb/v015/i002/2000GB001291/2000GB001291.pdf, 15(2), 483-506
[ Abstract ]
We establish the fixed nitrogen budget of the Pacific Ocean based on nutrient fields from the recently completed World Ocean Circulation Experiment (WOCE). The budget includes denitrification in the water column and sediments, nitrogen fixation, atmospheric and riverine inputs, and nitrogen divergence due to the large-scale circulation. A water column denitrification rate of 48 � 5 Tg N yr^-1 is calculated for the Eastern Tropical Pacific using N * [Gruber and Sarmiento,1997] and water mass age tracers. On the basis of rates in the literature, we estimate sedimentary denitrification to remove n additional 15 � 3 Tg N yr^-1. We then calculate the total nitrogen divergence due to the large scale circulation through the basin, composed of flows through a zonal transect at 32�S, and through the Indonesian and Bering straits. Adding atmospheric deposition and riverine fluxes results in a net divergence of nitrogen from the basin of -4 � 12 Tg N yr^-1. Pacific nitrogen fixation can be extracted as a residual component of the total budget, assuming steady state. We find that nitrogen fixation would have to contribute 59 � 14 Tg N yr^-1 in order to balance the Pacific nitrogen budget. This result is consistent with the tentative global extrapolations of Gruber and Sarmiento[ 1997], based on nitrogen fixation rates estimated for the North Atlantic. Our estimated mean areal fixation rate is within the range of direct and geochemical rate estimates from a single location near Hawaii [Karl et al., 1997]. Pacific nitrogen fixation occurs primarily in the western part of the subtropical gyres where elevated N* signals are found. These regions are also supplied with significant amounts of iron via atmospheric dust deposition, lending qualitative support to the hypothesis that nitrogen fixation is regulated in part by iron suppy.
Doney, S. C., J. Kleypas, Jorge Sarmiento, and P. G. Falkowski, 2001: The U. S. JGOFS Synthesis and Modeling Project -- An introduction. Deep Sea Research II, 49(1-3), doi:10.1016/S0967-0645(01)00092-3 1-20
[ Abstract ]
The field data collected as part of the international Joint Global Ocean Flux Study (JGOFS) provide an unprecedented view of marine biogeochemistry and the ocean carbon cycle. Following the completion of a series of regional process studies, a global CO₂ survey, and a decade of sampling at two open-ocean timeseries, US JGOFS initiated in 1997 a final research phase, the Synthesis and Modeling Project (SMP). The objective of the US JGOFS SMP is to ��synthesize knowledge gained from the US JGOFS and related studies into a set of models that reflect our current understanding of the oceanic carbon cycle��. Here we present an overview of the SMP and highlight the early scientific results from the project.
Gloor, M. N., N. Gruber, T.M.C. Hughes, and Jorge Sarmiento, 2001: Estimating Net Air-Sea Fluxes from Ocean Bulk Data: Methodology and Application to the Heat Cycle. Global Biogeochemical Cycles, 15(4), doi:10.1029/2000GB001301 767-782
[ Abstract ]
A novel method to estimate annual mean heat, water, and gas exchange fluxes between the ocean and the atmosphere is proposed that is complementary to the traditional approach based on air-sea gradients and bulk exchange parameterization. The new approach exploits the information on surface exchange fluxes contained in the distribution of temperature, salinity, and dissolved gases in the ocean interior. We use an Ocean General Circulation Model to determine how the distribution in the ocean interior is linked to surface fluxes. We then determine with least squares the surface fluxes that are most compatible with the observations. To establish and test the method, we apply it to ocean temperature data to estimate heat fluxes across the air-sea interface for which a number of climatological estimates exists. We also test the sensitivity of the inversion results to data coverage,differences in ocean transport, variations in the surface flux pattern and a range of spatial resolutions. We find, on the basis of the World Ocean Circulation Experiment( WOCE) data network augmented with selected high-quality pre-WOCE data, t hat we are able to constrain heat exchange fluxes for 10-15 regions of the ocean, whereby these fluxes nearly balance globally without enforcing a conservation constraint. Our results agree well with heat flux estimates on the basis of bulk exchange parameterization, which generally require constraints to ensure a global net heat flux of zero. We also find that the heat transports implied by our inversely estimated fluxes are in good agreement with a large range of heat transport estimates based on hydrographic data. Increasing the number of regions beyond the 10-15 regions considered here is severely limited because of modeling errors. The inverse method is fairly robust to the modeling of the spatial patterns of the surface fluxes; however, it is quite sensitive to the modeling of ocean transport. The most striking difference between our estimates and the heat flux climatologies is a large heat loss of 0.64 PW to the atmosphere from the Southern Ocean and a large heat gain by the subpolar South Atlantic of 0.56 PW. These results are consistent with the large gain of carbon dioxide called for by Takahashi et al. [1999] in his recent analysis of the air-sea flux of carbon dioxide but inconsistent with the large loss of oxygen and carbon dioxide such as those of Stephens et al. [1998].
Haug, G. H., K. A. Hughen, Daniel Sigman, L. C. Peterson, and U. Röhl, 2001: Southward migration of the Intertropical Convergence Zone through the Holocene. Science, 293, doi:10.1126/science.1059725 1304-1308
[ Abstract ]
Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene "thermal maximum". Since ˜ 5400 years ago, a trend toward drier conditions is evident from the data, with high-amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the "Little Ice Age". These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.
Keeling, R. F., H. B. Wilson, and Stephen W. Pacala, 2001: Deterministic limits to stochastic spatial models of natural enemies. American Naturalist, 159(1), doi:10.1086/324119 57-80
[ Abstract ]
Stochastic spatial models are becoming an increasingly popular tool for understanding ecological and epidemiological problems. However, due to the complexities inherent in such models, it has been difficult to obtain any analytical insights. Here, we consider individual-based, stochastic models of both the continuous time Lotka-Volterra system and the discrete-time Nicholson-Bailey model. The stability of these two stochastic models of natural enemies is assessed by constructing moment equations. The inclusion of these moments, which mimic the effects of spatial aggregation, can produce either stabilizing or destabilizing influences on the population dynamics. Throughout, the theoretical results are compared to numerical models for the full distribution of populations, as well as stochastic simulations.
Keller, Klaus, R. D. Slater, Michael Bender, and R. M. Key, 2001: Possible biological or physical explanations for decadal scale trends in North Pacific nutrient concentrations and oxygen utilization. Deep Sea Research II, 49(103), doi:10.1016/S0967-0645(01)00106-0 345-362
[ Abstract ]
We analyze North Pacific GEOSECS (1970s) and WOCE (1990s) observations to examine potential decadal trends of the marine biological carbon pump. Nitrate concentrations {[NO₃]} and apparent oxygen utilization (AOU) decreased significantly in intermediate waters (by - 0.6 and - 2.9 μmol kg^-1; respectively, at σ_θ = 27.4 kg m^-3; corresponding to ≈ 1050 m). In shallow waters (above roughly 750 m) [NO₃] and AOU increased, though the changes were not statistically significant. A sensitivity study with an ocean general circulation model indicates that reasonable perturbations of the biological carbon pump due to changes in export production or remineralization efficiency are insufficient to account for the intermediate water tracer trends. However, changes in water ventilation rates could explain the intermediate water tracer trends and would be consistent with trends of water age derived from radiocarbon. Trends in AOU and [NO₃] provide relatively poor constraints on decadal scale trends in the marine biological carbon pump for two reasons. First, most of the expected changes due to decadal scale perturbations of the marine biota occur in shallow waters, where the available data are typically too sparse to account for the strong spatial and temporal variability. Second, alternative explanations for the observed tracer trends (e.g., changes in the water ventilation rates) cannot be firmly rejected. Our data analysis does not disprove the null hypothesis of an unchanged biological carbon pump in the North Pacific.
Moorcroft, P. R., G. C. Hurtt, and Stephen W. Pacala, 2001: A Method for Scaling Vegetation Dynamics: the Ecosystem Demography Model (ED). Ecological Monographs, 71(4), doi:10.1890/0012-9615(2001)071[0557:AMFSVD]2.0.CO;2 557-586
[ Abstract ]
The problem of scale has been a critical impediment to incorporating important fine-scale processes into global ecosystem models. Our knowledge of fine-scale physiological and ecological processes comes from a variety of measurements, ranging from forest plot inventories to remote sensing, made at spatial resolutions considerably smaller than the large scale at which global ecosystem models are defined. In this paper, we describe a new individual-based, terrestrial biosphere model, which we label the ecosystem demography model (ED). We then introduce a general method for scaling stochastic individual-based models of ecosystem dynamics (gap models) such as ED to large scales. The method accounts for the fine-scale spatial heterogeneity within an ecosystem caused by stochastic disturbance events, operating at scales down to individual canopy-tree-sized gaps. By conditioning appropriately on the occurrence of these events, we derive a size and age-structured (SAS) approximation for the first moment of the stochastic ecosystem model. With this approximation, it is possible to make predictions about the large scales of interest from a description of the fine-scale physiological and population-dynamic processes without simulating the fate of every plant individually. We use the SAS approximation to implement our individual-based biosphere model over South America from 15� N to 15� S, showing that the SAS equations are accurate across a range of environmental conditions and resulting ecosystem types. We then compare the predictions of the biosphere model to regional data and to intensive data at specific sites. Analysis of the model at these sites illustrates the importance of fine-scale heterogeneity in governing large-scale ecosystem function, showing how population and community-level processes influence ecosystem composition and structure, patterns of above ground carbon accumulation, and net ecosystem production.
Oppenheimer, Michael, et al., 2001: Technical Summary and Summary for Policy Makers. Climate Change 2001: The Science of Climate Change. 3rd Assessment Report of the IPCC, Cambridge University Press,
[ Abstract ]
Climate Change 2001: The Scientific Basis is the most comprehensive and up-to-date scientific assessment of past, present and future climate change. The report:
� Analyses an enormous body of observations of all parts of the climate system. � Catalogues increasing concentrations of atmospheric greenhouse gases. � Assesses our understanding of the processes and feedbacks which govern the climate system. � Projects scenarios of future climate change using a wide range of models of future emissions of greenhouse gases and aerosols. � Makes a detailed study of whether a human influence on climate can be identified. � Suggests gaps in information and understanding that remain in our knowledge of climate change and how these might be addressed. Simply put, this latest assessment of the IPCC will again form the standard scientific reference for all those concerned with climate change and its consequences, including students and researchers in environmental science, meteorology, climatology, biology, ecology and atmospheric chemistry, and policymakers in governments and industry worldwide. J.T.
Orr, J. C., E. Maier-Reimer, U. Mikolajewicz, P. Monfray, Jorge Sarmiento, J. R. Toggweiler, N. K. Taylor, J. Palmer, N. Gruber, C. L. Sabine, C. Le Quere, R. M. Key, and J. Boutin, 2001: Estimates of anthropogenic carbon uptake from four three-dimensional global ocean models. Global Biogeochemical Cycles, http://www.agu.org/pubs/crossref/2001/2000GB001273.shtml, 15(1), 43-60
[ Abstract ]
We have compared simulations of anthropogenic CO₂ in the four three dimensional ocean models that participated in the first phase of the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP), as a means to identify their major differences. Simulated global uptake agrees to within �19%, giving a range of 1.85 � 0.35 Pg Cy r^-1 for the 1980-1989 average. Regionally, t he Southern Ocean dominates the present-day air-sea flux of anthropogenic CO₂ in all models, with one third to one half of the global uptake occurring south of 30�S. The highest simulated total uptake in the Southern Ocean was 70% larger than the lowest. Comparison with recent data-based estimates of anthropogenic CO₂ suggest that most of the models substantially overestimate storage in the Southern Ocean; elsewhere they generally underestimate storage by less than 20%. Globally, the OCMIP models appear to bracket the real ocean's present uptake, based on comparison of regional data-based estimates of anthropogenic CO₂ and bomb ¹⁴C. Column inventories of bomb ¹⁴C have become more similar to those for anthropogenic CO₂ with the time that has elapsed between the Geochemical Ocean Sections Study (1970s) and Word Ocean Circulation Experiment ( 1990s) global sampling campaigns. Our ability to evaluate simulated anthropogenic CO₂ would improve if systematic errors associated with the data-based estimates could be provided regionally.
Pacala, Stephen W., G. C. Hurtt, P. R. Moorcroft, and J. P. Caspersen, 2001: Carbon storage in the US caused by land use change. The Present and Future of Modeling Global Environmental Change, Terra Scientific Publishing, Tokyo, Japan, http://www.terrapub.co.jp/e-library/toyota/pdf/145.pdf, 145-172
[ Abstract ]
Here we examine the cause, size and future of the U.S. carbon sink. To estimate the size of the U.S. carbon sink we review a comprehensive land-based analysis of the carbon sink in the coterminous U.S. For the 1980s, the sink is between 1/3 and 2/3 PgC y^-1, and is split approximately evenly between forest and non-forest sectors. The non-forest sink is caused by fire suppression on non-forested lands, sediment burial in reservoirs, alluvium and colluvium, and agricultural practices.
The forest sink has been attributed to changes in land use and the enhancement of plant growth by CO₂ fertilization, N deposition and climate change. To estimate the relative contribution of land use and growth enhancement in forest ecosystems, we use forest inventory data from five states spanning a latitudinal gradient in the eastern U.S. Land use is the dominant factor governing the rate of carbon accumulation in forests in these states, with growth enhancement contributing far less than previously reported. The estimated fraction of above-ground net ecosystem production due to growth enhancement is 2.0 � � 4.4%, with the remainder due to land use.
To forecast the future of the U.S. carbon sink, we used the Ecosystem Demography Model (ED). We first modeled carbon sources and sinks from 1700�1990, and then projected patterns to 2100. Our projections indicate that the land-use portion of the U.S. carbon sink will decrease in the future, with a half-life of approximately 50 years, as U.S. ecosystems gradually equilibrate with current patterns of natural and anthropogenic disturbance.
Inventories of terrestrial carbon storage in the coterminous United States (the U.S. minus Alaska and Hawaii) appear to support the conclusion that the sink is small (4). However, inventories in the Northern Hemisphere have been able to account for only a third or less of the 1�2 PgC y^-1 indicated strongly by other lines of evidence (5). Moreover, the two primary groups of U.S. inventory studies strongly disagree about cause of the U.S. sink. Houghton and his colleagues (6) used historical records of land use change, timber production, soil conservation, wildfire rates, and simple models of carbon gains and losses in vegetation, soils and wood products. They estimated a sink for the coterminous U.S. averaging 0.39 PgC y^-1 from 1950�1990, and caused primarily by increases in crop productivity and changes in the management of agricultural soils (0.15 PgC), and by fire suppression on non-forested land (0.13 Pg C). They concluded that the entire forest sector contributed only 0.07�0.12 PgC y^-1.
The U.S. Forest Service (USFS) estimated a coterminous U.S. sink averaging 0.33 PgC y^�1 from 1952�1992, using census and tree measurement data from the over 100,000 plots in their Forest Inventory and Analysis (FIA) network, together with models of soil carbon and the fate of wood products (7). Although 0.33 Pg is close to 0.39 Pg, the entire USFS estimate is for the forest sector. If all of the carbon identified in both (6) and (7) were real, then the annual sink for the coterminous U.S. would be 0.60�0.65 PgC (0.33 from (7) plus 0.39 from (6) minus the forest sector estimates from (6)) and thus the overlap between the two estimates is only 11�20% of the total (0.07/0.65 to 0.12/0.60).
The FIA data base shows that the increase of carbon in trees has remained remarkably steady from 1952 to 1992, at approximately 0.10 + 0.02 PgC y^-1, because regrowth in the eastern half of the U.S. consistently exceeds harvest by about 0.1 PgC (7). This value is approximately double the increase in living forest carbon modeled in (6). To first order, differences among published inventories based on FIA data are caused by differences in the modeling of all forms of dead organic matter (including slash, wood products, standing dead trees, and soil carbon). For example, one study produced an estimate of only 0.08 PgC y^-1 for the 1980�s, because its modeling assumptions led to negligible accumulation of nonliving carbon (8). In contrast, the assumptions behind the USFS estimate of 0.33 PgC y^-1 implied that soil carbon accumulated twice as fast as living carbon in trees. In addition, no comprehensive inventory has as yet included the carbon sink caused by sediment burial in reservoirs, alluvium and colluvium and by the transport of carbon into the oceans by rivers. At least one study suggests that sediment burial and river transport may be significant (9). Finally, no comprehensive inventory accounts for net export of carbon in agricultural and wood products.
Ecosystem models provide the final source of information about the terrestrial carbon sink and generally produce small estimates for the coterminous U.S. For example, the models in the recently published VEMAP comparison produced estimates of 0.08 + 0.02 PgC y^-1 for the period from 1980�1993 (10). However, none of these models includes the land use changes (i.e. agricultural abandonment, fire suppression, forest harvesting and regrowth, no-till agriculture) that play such a dominant role in the inventory analyses. The models focus instead on the effects of climate change and CO₂ and nitrogen fertilization.
In what follows, we first summarize the results of a new inventory-based analysis of the coterminous U.S. carbon sink, which shows that the sink averages between one third and two thirds Pg annually (11). These estimates and smaller than the 0.81�0.84 PgC y^-1 in the controversial study (2) (see 11 for a discussion of the portion of estimates in (2) that correspond to the coterminous U.S.). However, they are significantly larger than the previously published range (one tenth to one third PgC y^-1). The analysis in (11) shows that approximately half the sink can be unambiguously ascribed to land use and management. We then summarize a recently published analysis (12) of the FIA data showing that the other half of the U.S. carbon sink is also overwhelmingly caused by land use and management.
Given that human land use rather than CO₂ or nitrogen fertilization or climate change causes the sink, it is interesting to consider the sink�s future. We then turn to two additional studies. The first (13), introduces a new model that incorporates the sub grid-scale heterogeneity necessary to simulate land use. The second (14), applies this model for the past 300 years of land use in the coterminous U.S., and shows that the U.S. sink will decrease throughout the coming century. Unlike sinks caused by fertilization or climate change that might increase, the land use sink will decrease as U.S. ecosystems adjust to the altered disturbance regimes created by land use and management.
Pacala, Stephen W., G. C. Hurtt, D. Baker, P. Peylin, R. A. Houghton, R. A. Birdsey, L. Heath, E. T. Sundquist, R. F. Stallard, P. Ciais, P. R. Moorcroft, J. P. Caspersen, and E. Shevliakova, et al., 2001: Consistent Land- and Atmosphere-Based U.S. Carbon Sink Estimates. Science, 292, doi:10.1126/science.1057320 2316-2320
[ Abstract ]
For the period 1980-89, we estimate a carbon sink in the coterminous United States between 0.30 and 0.58 petagrams of carbon per year (petagrams of carbon = 10¹⁵ grams of carbon). The net carbon �ux from the atmosphere to the land was higher, 0.37 to 0.71 petagrams of carbon per year, because a net �ux of 0.07 to 0.13 petagrams of carbon per year was exported by rivers and commerce and returned to the atmosphere elsewhere. These land-based estimates are larger than those from previous studies (0.08 to 0.35 petagrams of carbon per year) because of the inclusion of additional processes and revised estimates of some component fluxes. Although component estimates are uncertain, about one-half of the total is outside the forest sector. We also estimated the sink using atmospheric models and the atmospheric concentration of carbon dioxide (the tracer-transport inversion method). The range of results from the atmosphere-based inversions contains the land-based estimates. Atmosphere- and land-based estimates are thus consistent, within the large ranges of uncertainty for both methods. Atmosphere-based results for 1980-89 are similar to those for 1985-89 and 1990-94, indicating a relatively stable U.S. sink throughout the period.
Rees, M., R. C. Condit, M. Crawley, Stephen W. Pacala, and G. D. Tilman, 2001: Long-Term Study of Vegetation Dynamics. Science, 293, doi:10.1126/science.1062586 650-655
[ Abstract ]
By integrating a wide range of experimental, comparative, and theoretical approaches, ecologists are starting to gain a detailed understanding of the long-term dynamics of vegetation. We explore how patterns of variation in demographic traits among species have provided insight into the processes that structure plant communities. We find a common set of mechanisms, derived from ecological and evolutionary principles, that underlie the main forces shaping systems as diverse as annual plant communities and tropical forests. Trait variation between species maintains diversity and has important implications for ecosystem processes. Hence, greater understanding of how Earth�s vegetation functions will likely require integration of ecosystem science with ideas from plant evolutionary, population, and community ecology.
Schimel, D., J. J. House, K. A. Hibbard, P. Bousquet, P. Ciais, P. Peylin, B. H. Brasswell, M. J. Apps, D. Baker, A. Bondeau, J. Canadell, G. Churkina, W. Cramer, A. S. Denning, C. B. Field, P. Friedlingstein, C. L. Goodale, M. Heimann, R. A. Houghton, J. M. Melillo, B. Moore III, D. Murdiyarso, I. Noble, and Stephen W. Pacala, et al., 2001: Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems. Nature, 414, doi:10.1038/35102500 169-172
[ Abstract ]
Knowledge of carbon exchange between the atmosphere, land and the oceans is important, given that the terrestrial and marine environments are currently absorbing about half of the carbon dioxide that is emitted by fossil-fuel combustion. This carbon uptake is therefore limiting the extent of atmospheric and climatic change, but its long-term nature remains uncertain. Here we provide an overview of the current state of knowledge of global and regional patterns of carbon exchange by terrestrial ecosystems. Atmospheric carbon dioxide and oxygen data confirm that the terrestrial biosphere was largely neutral with respect to net carbon exchange during the 1980s, but became a net carbon sink in the 1990s. This recent sink can be largely attributed to northern extratropical areas, and is roughly split between North America and Eurasia. Tropical land areas, however, were approximately in balance with respect to carbon exchange, implying a carbon sink that offset emissions due to tropical deforestation. The evolution of the terrestrial carbon sink is largely the result of changes in land use over time, such as regrowth on abandoned agricultural land and fire prevention, in addition to responses to environmental changes, such as longer growing seasons, and fertilization by carbon dioxide and nitrogen. Nevertheless, there remain considerable uncertainties as to the magnitude of the sink in different regions and the contribution of different processes.
Schneider, L. C., A. P. Kinzig, Eric Larson, and L. A. Solarzano, 2001: Method for Spatially-Explicit Calculations of Potential Biomass Yields and Assessment of Land Availability for Biomass Energy Production in Northeastern Brazil. Agriculture, Ecosystems, and Environment, 84(3), doi:10.1016/S0167-8809(00)00242-5 207-226
[ Abstract ]
The Intergovernmental Panel on Climate Change (IPCC) has suggested that large-scale use of carbon-neutral or low-carbon biomass-derived energy will be essential in order to limit carbon emissions from the world�s energy sector in the future. The IPCC envisions as much as 400 million ha being devoted to biomass energy plantations by 2050. To realize production of biomass energy at such levels�in a manner that would be both biogeophysically sustainable and socially beneficial�will require planning and policy development at sub-national levels, taking into account biogeophysical, social, cultural, economic, institutional, and other factors. This paper presents amethod for spatially explicit calculations for estimating potential biomass yields over relatively large geographic regions. The calculations use geo-referenced data inputs that include rainfall, insolation, temperature, soil quality, and soil depth. The methodology is applied to the Northeast region of Brazil, which accounts for 10% of the area of South America. Northeast Brazil is an interesting site for illustrative purposes in part because it is biologically, geologically, and socio-economically diverse and in part because the main electric utility serving the region is exploring the development of biomass-based electricity generation to meet future increases in electricity demand. Results from a spatially explicit, biogeophysical model like that presented here could be combined with other spatially explicit information such as road layouts, existing land uses, population densities and growth rates, distributions of endangered species, archeologically significant areas, etc. to inform planning and policy development related to biomass energy at a regional or national level. One illustration of such an analysis is included here. For on-the-ground implementation of biomass production systems, finer-resolution analysis and intimate local participation is essential.
Sigman, Daniel, and K. L. Casciotti, 2001: Nitrogen isotopes in the ocean. Encyclopedia of Ocean Sciences, London, Academic Press, doi:10.1006/rwos.2001.0172 1884-1894
[ Abstract ]
Nitrogen has two stable isotopes, ¹⁴ N and ¹⁵ N (atomic masses of 14 and 15, respectively). ¹⁴ N is the more abundant of the two, comprising 99.63% of the nitrogen found in nature. Physical, chemical, and biological processes discriminate between the two isotopes. This is known as isotopic fractionation, and it leads to subtle but measurable differences in the ratio of ¹⁵ N to ¹⁴ N among different forms of nitrogen found in the marine environment. Nitrogen is a central component of marine biomass and one of the major nutrients required by all phytoplankton. In this sense, biologically available (or �fixed�) N is representative of the fundamental patterns of biogeochemical cycling in the ocean. However, N differs from other nutrients in that its oceanic sources and sinks are dominantly internal and biological, with marine N₂ fixation supplying much of the fixed N in the ocean and marine denitrification removing it. The N isotopes provide a means of studying both the internal cycling and input/output budget of oceanic fixed N, yielding information on both its representative and unique aspects. This overview outlines the isotope systematics of N cycle processes and their impacts on the isotopic composition of the major N reservoirs in the ocean. This information provides a starting point for considering the wide range of questions in ocean sciences to which the N isotopes can be applied.
Sigman, Daniel, K. L. Casciotti, M. Andreani, C. Barford, M. Galanter, and J. K. Böhlke, 2001: A bacterial method for the nitrogen isotopic analysis of nitrate in seawater and freshwater. Analytical Chemistry, 73(17), doi:10.1021/ac010088e 4145-4153
[ Abstract ]
We report a new method for measurement of the isotopic composition of nitrate (NO₃ -) at the natural-abundance level in both seawater and freshwater. The method is based on the isotopic analysis of nitrous oxide (N₂O) generated from nitrate by denitrifying bacteria that lack N₂O-reductase activity. The isotopic composition of both nitrogen and oxygen from nitrate are accessible in this way. In this first of two companion manuscripts, we describe the basic protocol and results for the nitrogen isotopes. The precision of the method is better than 0.2� (1 SD) at concentrations of nitrate down to 1 μM, and the nitrogen isotopic differences among various standards and samples are accurately reproduced. For samples with 1 μM nitrate or more, the blank of the method is less than 10% of the signal size, and various approaches may reduce it further.
Socolow, Robert H., 2001: Scale, Awareness, and Conscience: The Moral Terrain of Ecological Vulnerability. New Dimensions in Bioethics, Norwell, MA, A. W. Galston and E. G. Schurr, eds., Kluwer Academic Publishers, (ISBN: 0792372492), 65-78
[ Abstract ]
Prosperity is stressing the environment. This interaction can be illuminated by separating out aggregate size (scale) available science (awareness), and the obligation to respond (conscience). Solutions require an evolving vision of the good life, a sustained commitment to open science, and both an active and reverent management of the Earth.
Socolow, Robert H., et al., 2001: An Assessment of the Department of Energy�s Office of Fusion Energy Sciences Program (contributor). Fusion Science Assessment Committee, Washington, D.C., National Academy Press, (ISBN: 10:0-309-07345),
[ Abstract ]
The purpose of this assessment of the fusion energy sciences program of the Department of Energy's (DOE's) Office of Science is to evaluate the quality of the research program and to provide guidance for the future program strategy aimed at strengthening the research component of the program. The committee focused its review of the fusion program on magnetic confinement, or magnetic fusion energy (MFE), and touched only briefly on intertial fusion energy (IFE), because MFE_relevant research accounts for roughly 95 percent of the funding in the Office of Science's fusion program. Unless otherwise noted, all references to fusion in this report should be assumed to refer to magnetic fusion.
Socolow, Robert H., May 1999: Nitrogen management and the future of food: Lessons from the management of energy and carbon. Proceedings of the National Academy of Sciences of the United States of America, http://www.pnas.org/content/96/11/6001.full.pdf, 6001-6008
[ Abstract ]
The food system dominates anthropogenic disruption of the nitrogen cycle by generating excess fixed nitrogen. Excess fixed nitrogen, in various guises, augments the greenhouse effect, diminishes stratospheric ozone, promotes smog, contaminates drinking water, acidifies rain, eutrophies bays and estuaries, and stresses ecosystems. Yet, to date, regulatory efforts to limit these disruptions largely ignore the food system. There are many parallels between food and energy. Food is to nitrogen as energy is to carbon. Nitrogen fertilizer is analogous to fossil fuel. Organic agriculture and agricultural biotechnology play roles analogous to renewable energy and nuclear power in political discourse. Nutrition research resembles energy end-use analysis. Meat is the electricity of food. As the agriculture and food system evolves to contain its impacts on the nitrogen cycle, several lessons can be extracted from energy and carbon: (i) set the goal of ecosystem stabilization; (ii) search the entire production and consumption system (grain, livestock, food distribution, and diet) for opportunities to improve efficiency; (iii) implement cap-and-trade systems for fixed nitrogen; (iv) expand research at the intersection of agriculture and ecology, and (v) focus on the food choices of the prosperous. There are important nitrogen-carbon links. The global increase in fixed nitrogen may be fertilizing the Earth, transferring significant amounts of carbon from the atmosphere to the biosphere, and mitigating global warming. A modern biofuels industry someday may produce biofuels from crop residues or dedicated energy crops, reducing the rate of fossil fuel use, while losses of nitrogen and other nutrients are minimized.
Socolow, Robert H., and V. Thomas, 1997: The Industrial Ecology of Lead and Electric Vehicles. Journal of Industrial Ecology, Cambridge, MA, MIT Press, 1(1), doi:10.1162/jiec.1997.1.1.13 13-36
[ Abstract ]
The lead battery has the potential to become one of the first examples of a hazardous product managed in an environmentally acceptable fashion. The tools of industrial ecology are helpful in identifying the key criteria that an ideal lead-battery recycling system must meet maximal recovery of batteries after use, minimal export of used batteries to countries where environmental controls are weak, minimal impact on the health of communities near lead processing facilities, and maximal worker protection from lead exposure in these facilities. A well-known risk analysis of electric vehicles is misguided, because it treats lead batteries and lead additives in gasoline on the same footing and implies that the lead battery should be abandoned. The use of lead additives in gasoline is a dissipative use where emissions cannot be confined: the goal of management should be and has been to phase out this use. The use of lead in batteries is a recyclable use, because the lead remains confined during cycles of discharge and recharge. Here, the goal should be clean recycling. The likelihood that the lead battery will provide peaking power for several kinds of hybrid vehicles-a role only recently identified increases the importance of understanding the levels of performance achieved and achievable in battery recycling. A management system closely approaching clean recycling should be achievable.
Bianchi, D., Jorge Sarmiento, A. Gnanadesikan, R. M. Key, P. Schlosser, and R. Newton, in press: Simulations of oceanic 3HE distribution suggest low rates of mantle degassing. Nature Geosciences. 0/00.
Hurtt, G. C., Stephen W. Pacala, P. R. Moorcroft, J. P. Caspersen, E. Shevliakova, R. A. Houghton, and B. Moore III, 0000: Projecting the Future of the U.S. Carbon Sink. Proceedings of the National Academy of Sciences of the United States of America, 99(3), doi:10.1073/pnas.012249999 1389-1394
[ Abstract ]
Atmospheric and ground-based methods agree on the presence of a carbon sink in the coterminous United States (the United States minus Alaska and Hawaii), and the primary causes for the sink recently have been identified. Projecting the future behavior of the sink is necessary for projecting future net emissions. Here we use two models, the Ecosystem Demography model and a second simpler empirically based model (Miami Land Use History), to estimate the spatio-temporal patterns of ecosystem carbon stocks and fluxes resulting from land-use changes and fire suppression from 1700 to 2100. Our results are compared with other historical reconstructions of ecosystem carbon fluxes and to a detailed carbon budget for the 1980s. Our projections indicate that the ecosystem recovery processes that are primarily responsible for the contemporary U.S. carbon sink will slow over the next century, resulting in a significant reduction of the sink. The projected rate of decrease depends strongly on scenarios of future land use and the long-term effectiveness of fire suppression.
Rodgers, K. B., and D. Bianchi, et al., in press: A Southern Ocean mechanism for atmospheric and oceanic Δ14C variations on centennial timescales. Paleoceanography. 0/00.

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