Net terrestrial CO2 exchange over China during 2001–2010 estimated with an ensemble data assimilation system for atmospheric CO2

In this paper we present an estimate of net ecosystem CO2 exchange over China for the years 2001–2010 using the CarbonTracker Data Assimilation System for CO2 (CTDAS). Additional Chinese and Asian CO2 observations are used in CTDAS to improve our estimate. We found that the combined terrestrial ecosystems in China absorbed about −0.33 Pg C yr−1 during 2001–2010. The uncertainty on Chinese terrestrial carbon exchange estimates as derived from a set of sensitivity experiments suggests a range of −0.29 to −0.64 Pg C yr−1. This total Chinese terrestrial CO2 sink is attributed to the three major biomes (forests, croplands, and grass/shrublands) with estimated CO2 fluxes of −0.12 Pg C yr−1 (range from −0.09 to −0.19 Pg C yr−1), −0.12 Pg C yr−1 (range from −0.09 to −0.26 Pg C yr−1), and −0.09 Pg C yr−1 (range from −0.09 to −0.17 Pg C yr−1), respectively. The peak‐to‐peak amplitude of interannual variability of the Chinese terrestrial ecosystem carbon flux is 0.21 Pg C yr−1 (~64% of mean annual average), with the smallest CO2 sink (−0.19 Pg C yr−1) in 2003 and the largest CO2 sink (−0.40 Pg C yr−1) in 2007. We stress that our estimate of terrestrial ecosystem CO2 uptake based on inverse modeling strongly depends on a limited number of atmospheric CO2 observations used. More observations in China specifically and in Asia in general are needed to improve the accuracy of terrestrial carbon budgeting for this region. Chinese terrestrial CO2 flux were estimated by CTDAS Most Chinese land ecosystems was CO2 sinks with large interannual variability More atmospheric CO2 observations within and surrounding China are needed