Terrestrial ecosystems play a significant role in the global carbon cycle and offset a large fraction of anthropogenic CO2 emissions. The terrestrial carbon sink is increasing, yet the mechanisms responsible for its enhancement, and implications for the growth rate of atmospheric CO2, remain unclear. Here using global carbon budget estimates, ground, atmospheric and satellite observations, and multiple global vegetation models, we examine long-term terrestrial carbon sink dynamics and attribute observed and modeled changes to quantify the effects of rising CO2 on terrestrial ecosystems.
Results/Conclusions
We report a secular increase in the terrestrial carbon sink that is driven primarily by both direct and indirect effects of rising CO2. We explore evidence for both a direct effect on plant light- and water-use efficiencies, and an indirect effect on vegetation cover through water savings and warming. The early 2000's pause in the growth rate of atmospheric CO2, and a decline in the fraction of anthropogenic emissions that remain in the atmosphere, despite increasing anthropogenic emissions, provide further evidence of an increasing sink. Evidence for an increasing sink highlights the need to protect both existing carbon stocks and regions where the sink is growing rapidly. We conclude that although the sink has been rising due to CO2 fertilization, the trend is likely to reverse in the coming decades.