Carbon Mitigation Initiative

2010 Year Annual Report:
Carbon Policy & Integration: Policy-Relevant Research

Safe vs. Fair - Perspectives on Historical Emissions

Rob Socolow and post-docs Shoibal Chakravarty and Massimo Tavoni produced a paper in 2010 dealing with the climate consequences of basing future national emissions on two ethical principles: equal emissions rights for all individuals and redress for historical emissions by the countries that industrialized early. The paper, now in internal review, is tentatively called "Safe vs. Fair." It displays the tension between achieving fair moral norms and reducing the prospect of great disruption from climate change by providing a simple mathematical representation of the underlying issues.

IPCC and Uncertainty

Rob Socolow is contributing a paper for a special issue of Climatic Change edited by Michael Oppenheimer and Gary Yohe, in which all articles will address the communication of uncertainty in IPCC reports with the intention of improving the Fifth Assessment Reports now being written. His article draws from his experiences as a member of the Committee on America's Climate Choices of the National Academy of Sciences, where he used the Fourth Assessment Reports to capture for policymakers what climate science can say about "high-consequence outcomes." He urges that the writers of each section of the Fifth Assessment Reports enrich their communication of uncertainty by communicating the degree of alignment of their views about the same evidence, rather than confining their discussion of uncertainty exclusively to the consistency of the science.

Lessons from Environmental Science Assessments

Michael Oppenheimer and colleagues are continuing their research on past environmental science and scientific assessments. The role of scientific assessments in the evaluation of knowledge has expanded over the past three or four decades to become an integral factor in shaping government policy on climate change. But how well have these scientific assessments worked, and how might they be made to work more efficiently and effectively in the future? Lessons from past cases may yield important insights for future climate policy.

Keynyn Brysse, a historian of science, has completed two years of a three-year postdoctoral research project to investigate the history of scientific assessments of ozone depletion. This ozone history project at Princeton is one part of an interdisciplinary, multi-university research project that this year was awarded a grant from the National Science Foundation's Science, Technology, and Society Program. The principal investigators on the grant are historian of science Naomi Oreskes at the University of California, San Diego; climate scientist Michael Oppenheimer at Princeton University; and philosopher of science Dale Jamieson at New York University. In addition to the research on ozone, the project, "Assessing assessments: a historical and philosophical study of scientific assessments for environmental policy in the late 20th century," is also examining the Intergovernmental Panel on Climate Change and acid rain assessments. The outcome of this interdisciplinary collaboration includes a series of conference presentations and peer-reviewed articles, as well as a book on the history of environmental science assessments and the lessons history can bring to future assessments, such as those dealing with climate change.

Understanding and Assessing Ice Sheet-Driven Sea Level Rise

Despite increasing awareness of the potential for rapid ice sheet change, sea level rise (SLR) projections in the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC) decreased as their uncertainty range narrowed. A dynamic response of land-based ice was not included in the numerical projections.

Effective policy decisions demand a more complete and transparent accounting of sources of sea level change and their associated uncertainty. However, weak observational constraints on the century-timescale ice sheet response, and the lack of a comprehensive model, have led to difficulties in quantifying the SLR contribution of Antarctica and Greenland. Michael Oppenheimer and colleagues are addressing these issues by 1) improving the comprehensiveness and robustness of ice sheet models and 2) presenting ice sheet projections in a form that is amenable to mitigation- and adaptation-related decision-making.

Ice Sheet-Ocean Coupled Modeling

Improving the representation of ice-ocean interaction at the margins of ice sheets, where recent acceleration and thinning is focused, is important to projections of future sea level. Floating ice shelves control how fast ice is transferred from the grounded ice sheet; from the oceanographic perspective, melting and freezing influences the characteristics of water masses (i.e. Ice Shelf Water, Antarctic Bottom Water, etc.), the global ocean circulation, and the carbon cycle.

WWS/STEP Postdoctoral Fellow Christopher Little, in collaboration with Daniel Goldberg, an AOS/WWS postdoctoral fellow, has investigated ice shelf melting using the Generalized Ocean Layered Dynamics (GOLD) ocean model (a NOAA ocean model, developed by GFDL oceanographer Dr. Robert Hallberg), and a dynamic ice stream/shelf model coupled to the GOLD ocean model. These simulations suggest that grounded ice loss shows an increasing response to ocean temperature rise that is driven by the distribution of ice shelf melting, demonstrating the importance of coupling the ocean and land ice in numerical simulations of climate change. Little and Goldberg's experiments also highlight the influence of the ice shelf calving, and a proposed collaborative project between Dr. Olga Sergienko (GFDL) and Allan Rubin (GEO), aims to apply fracture mechanics to the calving problem.

Improving the Utility of Sea Level Projections

Given the early stage of coupled climate/ice sheet model development, Little and colleagues are employing expertise in risk assessment, learning, and statistical analysis to develop new ways to project sea level change in a decision-relevant context. Historical analyses of environmental risk assessments suggest that any approach to ice sheet-driven SLR projection should be systematic, inclusive, and serve as a framework for learning. When assessments are opaque, the lack of transparency hinders efforts to update and compare; if sea level rise originates outside of these regions, it will diminish the reliability of the upper bound.

Recently, the researchers have cast projections of Antarctic ice stream discharge in a bottom-up Monte Carlo approach to examine the sensitivity to key assumptions. Their results indicate that the form of ice discharge scenarios, their associated uncertainty, and the correlation in mass loss between ice drainages control the tail area of sea level distributions (the information that is most relevant for climate policy and coastal management decisions). Therefore, ignoring regions is a questionable prior assumption, even if their most likely contribution is zero. In this comprehensive, probabilistic framework, subjective judgments may be made in a transparent fashion, facilitating assessment (e.g. in IPCC AR5) via risk and sensitivity analyses. This approach allows the incorporation of dynamic regional or continental-scale models, allowing a revisiting of the uncertainty as more is learned about the ice sheets and climate forcing.

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