Bibliography - David Medvigy

1. 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.

2. 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.

Direct link to page: http://cmi.princeton.edu/bibliography/results.php?author=4712