China's terrestrial carbon balance: Contributions from multiple global change factors
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The magnitude, spatial, and temporal patterns of the terrestrial carbon sink and theunderlying mechanisms remain uncertain and need to be investigated. China is importantin determining the global carbon balance in terms of both carbon emission and carbonuptake. Of particular importance to climate‐change policy and carbon management is theability to evaluate the relative contributions of multiple environmental factors to net carbonsource and sink in China’s terrestrial ecosystems. Here the effects of multipleenvironmental factors (climate, atmospheric CO2, ozone pollution, nitrogen deposition,nitrogen fertilizer application, and land cover/land use change) on net carbon balance interrestrial ecosystems of China for the period 1961–2005 were modeled with newlydeveloped, detailed historical information of these changes. For this period, results fromtwo models indicated a mean land sink of 0.21 Pg C per year, with a multimodel rangefrom 0.18 to 0.24 Pg C per year. The models’ results are consistent with field observationsand national inventory data and provide insights into the biogeochemical mechanismsresponsible for the carbon sink in China’s land ecosystems. In the simulations, nitrogendeposition and fertilizer applications together accounted for 61 percent of the net carbonstorage in China’s land ecosystems in recent decades, with atmospheric CO2increasesand land use also functioning to stimulate carbon storage. The size of the modeledcarbon sink over the period 1961–2005 was reduced by both ozone pollution and climatechange. The modeled carbon sink in response to per unit nitrogen deposition shows aleveling off or a decline in some areas in recent years, although the nitrogen input levelshave continued to increase.