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

Abstract

<p>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.</p>