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

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 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 with an interquartile
of 33–46 PgC/yr —a much smaller portion of net primary productivity than previously reported.