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Empirical estimates of regional carbon budgets imply reduced global soil heterotrophic respiration

Philippe Ciais, Yitong Yao, Thomas Gasser, Alessandro Baccini, Yilong Wang, Ronny Lauerwald, Shushi Peng, Ana Bastos, Wei Li, Peter A Raymond, Josep G. Canadell, Glen Peters, Robert J. Andres, Jinfeng Chang, Chao Yue, A. Johannes Dolman, Vanessa Haverd, Jens Hartmann, Goulven Laruelle, Alexandra G Konings, Anthony W King, Yi Liu, Sebastiaan Luyssaert, Fabienne Maignan, Prabir K. Patra, Anna Peregon, Pierre Regnier, Julia Pongratz, Ben Poulter, Anatoly Shvidenko, Riccardo Valentini, Rong Wang, Grégoire Broquet, Yi Yin, Jakob Zscheischler, Bertrand Guenet, Daniel S. Goll, Ashley P. Ballantyne, Hui Yang, Chunjing Qiu, Dan Zhu

Resolving regional carbon budgets is critical for informing land-based mitigation policy. For nine regions covering nearly the whole globe, we collected inventory estimates of carbon-stock changes complemented by satellite estimates of biomass changes where inventory data are missing. The net land–atmospheric carbon exchange (NEE) was calculated by taking the sum of the carbon-stock change and lateral carbon fluxes from crop and wood trade, and riverine-carbon export to the ocean. Summing up NEE from all regions, we obtained a global ‘bottom-up’ NEE for net land anthropogenic CO2 uptake of –2.2 ± 0.6 PgC yr−1 consistent with the independent top-down NEE from the global atmospheric carbon budget during 2000–2009. This estimate is so far the most comprehensive global bottom-up carbon budget accounting, which set up an important milestone for global carbon-cycle studies. By decomposing NEE into component fluxes, we found that global soil heterotrophic respiration amounts to a source of CO2 of 39 PgC yr−1 with an interquartile of 33–46 PgC yr−1—a much smaller portion of net primary productivity than previously reported.

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