Omitting C erosion by Wind in C Cycling Reveals Overestimated CO2 Emission and Unrecognised Uncertainty in Drylands.

Global models of the terrestrial C cycle were developed about two decades ago with the primary goal of projecting changes in terrestrial C storage under increasing atmospheric CO₂ concentration and climate change. The models (e.g., RothC) recognise that soil microorganisms are the main agents of decomposition of soil organic matter and that reductions in carbon stock are dominated by CO₂ emission. However, there is growing awareness that the reduction in C stock can also occur by lateral fluxes of C caused by wind, water and tillage. Here, we couple a C cycling model with a spatially and temporally dynamic global wind erosion model based on daily MODIS (500 m) albedo (MCD43A1) measurements. Globally we show that up to one third of the C assumed removed to the atmosphere by decomposition, is redistributed within the terrestrial ecosystem. Regionally, C erosion by wind in drylands matches the amount estimated to be decomposed. Previous model estimates of CO₂ emission are therefore over-estimated because they do not account for C erosion by wind. The implications are that current C budgets are more uncertain than previously recognised because they omit C erosion. Furthermore, drylands cover 45% of the terrestrial surface and are expected to warm by 3-4°C and experience a reduction in precipitation of 5-30 % by the end of this century. Consequently, soil moisture is likely to decrease by 25 % in many areas, impacting microbial activity, net primary productivity, C cycling and accelerating C loss by wind erosion. In Earth System Models, the omission of feedbacks and interactions between erosion, C and nutrient cycling make climate projections more uncertain than previously recognised.