Soil carbon simulation, projections and feedbacks in CMIP6 Earth system models

Understanding the sensitivity of soil carbon cycling to climate change is key to quantifying future carbon cycle feedbacks. Under increased atmospheric CO₂, both carbon input to the soil from vegetation and carbon output from the soil due to heterotrophic respiration will increase, and the balance between these will determine the future ability of the land surface to be a sink or source of carbon. The ability of Earth system models (ESMs) to simulate soil carbon and related processes is therefore vital for reliably estimating global carbon budgets required for emission policies. Soil carbon simulation, projections and feedbacks are evaluated in the latest generation of CMIP6 ESMs. Global soil carbon is compared against observational datasets, future changes in global soil carbon stores and fluxes are investigated, and the carbon cycle feedbacks are quantified. The results suggest much of the uncertainty associated with modelled soil carbon stocks can be attributed to the simulation and representation of below ground soil processes in large scale models. These improvements would help reduce the uncertainty in projected carbon release from global soils under increasing levels of global warming.