Global Carbon Budget Audit
Over the last 5 decades, monitoring systems have been developed to detect changes in carbon (C) accumulations in the atmosphere and oceans, but the ability to detect changes in the behavior of the global carbon cycle is still hindered by measurement and estimate errors. In a recent study, researchers developed a rigorous and flexible framework for assessing the temporal and spatial components of estimate errors and their impact on uncertainty in net carbon uptake by the biosphere. They present a novel approach for incorporating temporally correlated random error into the error structure of emission estimates. Based on this approach, they conclude that the 2σ uncertainties of the atmospheric growth rate have decreased from 1.2 Pg C yr-1 in the 1960s to 0.3 Pg C yr-1 in the 2000s due to an expansion of the atmospheric observation network. The 2σ uncertainties in fossil fuel emissions have increased from 0.3 Pg C yr-1 in the 1960s to almost 1.0 Pg C yr-1 during the 2000s due to differences in national reporting errors and differences in energy inventories. Lastly, while land use emissions have remained fairly constant, their errors still remain high and thus their global carbon uptake uncertainty is not trivial. Currently, the absolute errors in fossil fuel emissions rival the total emissions from land use, highlighting the extent to which fossil fuels dominate the global carbon budget. Because errors in the atmospheric growth rate have decreased faster than errors in total emissions have increased, a 20% reduction in the overall uncertainty of net carbon global uptake has occurred. Given all the major sources of error in the global carbon budget that could be identified, the results are 93% confident that terrestrial carbon uptake has increased and 97% confident that ocean carbon uptake has increased over the last 5 decades. Thus, arguably one of the most vital ecosystem services that the biosphere currently provides is the continued removal of approximately half of atmospheric carbon dioxide emissions from the atmosphere, although there are certain environmental costs associated with this service, such as the acidification of ocean waters.
Ballantyne, A. P., R. Andres, R. Houghton, B. D. Stocker, R. Wanninkhof, W. Anderegg, L. A. Cooper, M. DeGrandpre, P. P. Tans, J. B. Miller, C. Alden, and J. W. C. White. 2015. “Audit of the Global Carbon Budget: Estimate Errors and Their Impact on Uptake Uncertainty,” Biogeosciences 12(8), 2565–84. DOI: 10.5194/bg-12-2565-2015.