Soil carbon-concentration and carbon-climate feedbacks in CMIP6 Earth system models

Abstract. Achieving climate targets requires mitigation against climate change, but also understanding of the response of land and ocean carbon systems. In this context, global soil carbon stocks and its response to environmental changes is key. This paper quantifies the global soil carbon feedback to changes in atmospheric CO₂, and associated climate changes, for Earth system models (ESMs) in CMIP6. A standard approach is used to calculate carbon cycle feedbacks, defined here as soil specific carbon-concentration (β_s) and carbon-climate (γ_s) feedback parameters. The sensitivity to CO₂ is shown to dominate soil carbon changes at least up to a doubling of atmospheric CO₂. However, the sensitivity of soil carbon to climate change is found to become an increasingly important source of uncertainty under higher atmospheric CO₂ concentrations.