Net terrestrial CO₂exchange 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 CO 2 exchange over China for the years 2001-2010 using the CarbonTracker Data Assimilation System for CO 2 (CTDAS). Additional Chinese and Asian CO 2 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 CO 2 sink is attributed to the three major biomes (forests, croplands, and grass/shrublands) with estimated CO 2 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 CO 2 sink (0.19 Pg C yr 1 ) in 2003 and the largest CO 2 sink (0.40 Pg C yr 1 ) in 2007. We stress that our estimate of terrestrial ecosystem CO 2 uptake based on inverse modeling strongly depends on a limited number of atmospheric CO 2 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.