In this new paper researchers confirm that as carbon emissions continue to climb, so too has the Earth's capacity to absorb carbon dioxide from the atmosphere. About half of the emissions of CO2 each year remain in the atmosphere; the other half is taken up by the ecosystems on land and the oceans.
Measurements of the amount of carbon in the atmosphere and how it varies seasonally and geographically allow us to detect changes in the behavior of the global carbon cycle. This paper outlines a new framework for assessing errors and their impact on the uncertainties associated with calculating carbon sinks on land and in oceans. The researchers conclude that the greater certainty in atmospheric carbon measurements has led to an increased certainty in the calculated rate of carbon uptake by land and oceans. The scientists are confident that the rates have so far increased in proportion to emissions. Monitoring that uptake year by year is critical for understanding the carbon cycle and for knowing how to deal with it.
Abstract
Over the last 5 decades monitoring systems have been developed to detect changes in the accumulation of carbon (C) in the atmosphere and ocean; however, our ability to detect changes in the behavior of the global C cycle is still hindered by measurement and estimate errors. Here we present a rigorous and flexible framework for assessing the temporal and spatial components of estimate errors and their impact on uncertainty in net C uptake by the biosphere. We present a novel approach for incorporating temporally correlated random error into the error structure of emission estimates. Based on this approach, we 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 C 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 C 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 C global uptake has occurred. Given all the major sources of error in the global C budget that we could identify, we are 93% confident that terrestrial C uptake has increased and 97% confident that ocean C uptake has increased over the last 5 decades. Thus, it is clear that arguably one of the most vital ecosystem services currently provided by the biosphere is the continued removal of approximately half of atmospheric CO2 emissions from the atmosphere, although there are certain environmental costs associated with this service, such as the acidification of ocean waters.
Citation
Ballantyne, A. P., Andres, R., Houghton, R., Stocker, B. D., Wanninkhof, R., Anderegg, W., Cooper, L. A., DeGrandpre, M., Tans, P. P., Miller, J. B, Alden, C., White, J. W. C., (2015) Audit of the global carbon budget: estimate errors and their impact on uptake uncertainty, Biogeosciences, 12, 2565-2584
Read the paper here. See additional coverage by the Woods Hole Research Center (one of whose researchers co-authored the study) here.
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