Evaluation of soil carbon simulation in CMIP6 Earth System Models

Abstract. The response of soil carbon represents one of the key uncertainties in future climate change. The ability of Earth System Models (ESMs) to simulate present day soil carbon is therefore vital for reliable projections. In this study the most up-to-date CMIP6 ESMs are evaluated against empirical datasets to assess the ability of each model to simulate soil carbon and related controls: Net Primary Productivity (NPP) and soil carbon turnover time (τs). Comparing CMIP6 with CMIP5, uncertainties in modelled soil carbon remain, particularly the underestimation of northern high latitude soil carbon stocks. There is a robust improvement in the simulation of NPP in CMIP6 compared with CMIP5, however the same improvements are not seen in the simulation of τs. These results suggest a greater emphasis is required on improving the representation of below-ground soil processes in future developments of models. These improvements would help reduce the uncertainty of projected carbon release from global soils under climate change and to increase confidence in the carbon budgets associated with different levels of global warming.