Land use-induced soil carbon loss in the dry tropics nearly offsets gains in northern lands.

Abstract

Soil carbon changes are difficult to measure globally, and global models are poorly constrained. Here, we propose a framework to map annual changes in soil carbon and litter (SOCL) as the difference between the net land CO₂ flux from atmospheric inversions and satellite-based maps of biomass changes. We show that SOCL accumulated globally at a rate of about 0.34 ± 0.30 ( ± 1 sigma) billion tonnes of carbon per year (PgC yr^-¹) during 2011-2020. The largest SOCL sink is found in boreal regions (0.93 ± 0.45 PgC yr^-¹ in total) particularly in undisturbed peatlands and managed forests. The largest losses occur in the dry tropics (-0.50 ± 0.47 PgC yr^-¹) and correspond with agricultural expansion from land use change, cropland management and grazing. By contrast, forests in the wet tropics act as a net soil carbon sink (0.32 ± 0.35 PgC yr^-¹). Our findings highlight the large mitigation opportunities in the dry tropics to restore agricultural soil carbon.