Global soil organic carbon removal by water erosion under climate change and land use change during AD-1850-2005

Erosion is an Earth system process that transportscarbon laterally across the land surface and is currently ac-celerated by anthropogenic activities. Anthropogenic landcover change has accelerated soil erosion rates by rainfall andrunoff substantially, mobilizing vast quantities of soil organiccarbon (SOC) globally. At timescales of decennia to mil-lennia this mobilized SOC can significantly alter previouslyestimated carbon emissions from land use change (LUC).However, a full understanding of the impact of erosion onland–atmosphere carbon exchange is still missing. The aimof this study is to better constrain the terrestrial carbon fluxesby developing methods compatible with land surface mod-els (LSMs) in order to explicitly represent the links betweensoil erosion by rainfall and runoff and carbon dynamics. Forthis we use an emulator that represents the carbon cycle of aLSM, in combination with the Revised Universal Soil LossEquation (RUSLE) model. We applied this modeling frame-work at the global scale to evaluate the effects of potentialsoil erosion (soil removal only) in the presence of other per-turbations of the carbon cycle: elevated atmospheric CO2,climate variability, and LUC. We find that over the periodAD 1850–2005 acceleration of soil erosion leads to a totalpotential SOC removal flux of 74±18 Pg C, of which 79 %–85 % occurs on agricultural land and grassland. Using ourbest estimates for soil erosion we find that including soil ero-sion in the SOC-dynamics scheme results in an increase of62 % of the cumulative loss of SOC over 1850–2005 dueto the combined effects of climate variability, increasing at-mospheric CO2and LUC. This additional erosional loss de-creases the cumulative global carbon sink on land by 2 Pg ofcarbon for this specific period, with the largest effects foundfor the tropics, where deforestation and agricultural expan-sion increased soil erosion rates significantly. We concludethat the potential effect of soil erosion on the global SOCstock is comparable to the effects of climate or LUC. It isthus necessary to include soil erosion in assessments of LUCand evaluations of the terrestrial carbon cycle.