Mapping the net ecosystem exchange of CO2 of global terrestrial systems

Net ecosystem exchange of CO2 (NEE) is a useful tool to analyze the carbon balance of different areas. Since it is impossible to measure NEE in-situ at a regional or global scale, this study has conducted a NEE estimation model to map the NEE of global terrestrial systems. By training the model with 2774 series of data collected from the database of AmeriFlux and Fluxnet, and relevant studies, the model has achieved a substantial global NEE estimation with R2 = 0.60, 0.68, and 0.67 for arable land, forest, and grassland systems. According to the estimation, the average annual global NEE was-18.41 billion tons C. Asia was the continent who had the highest NEE (33.93% of global NEE), and forests were the ecosystems who contributed most to global CO2 absorption (51.75% of global NEE). When comparing with the global CO2 emissions, the model results also showed that Asia, North America, and Europe have run out of their ecosystem potential to absorb the CO2 emitted. The countries with top 10 greatest C emission had smaller effective NEEs to deal with their own emitted C except Russia and Canada. Considering the economic contribution of different countries, NEE estimation model could be a helpful tool to achieve a better fairness of controlling C emission tasks by considering both C emission gen-eration and natural C emission handling ability.