Higher climatological temperature sensitivity of soil carbon in cold than warm climates

Abstract

Soil carbon release remains a highly uncertain climate feedback. Research now shows that the temperature control on carbon turnover is more sensitive in cold climates, supporting projections of a strong carbon–climate feedback from northern soils. The projected loss of soil carbon to the atmosphere resulting from climate change is a potentially large but highly uncertain feedback to warming. The magnitude of this feedback is poorly constrained by observations and theory, and is disparately represented in Earth system models (ESMs)1,2,3. To assess the climatological temperature sensitivity of soil carbon, we calculate apparent soil carbon turnover times4 that reflect long-term and broad-scale rates of decomposition. Here, we show that the climatological temperature control on carbon turnover in the top metre of global soils is more sensitive in cold climates than in warm climates and argue that it is critical to capture this emergent ecosystem property in global-scale models. We present a simplified model that explains the observed high cold-climate sensitivity using only the physical scaling of soil freeze–thaw state across climate gradients. Current ESMs fail to capture this pattern, except in an ESM that explicitly resolves vertical gradients in soil climate and carbon turnover. An observed weak tropical temperature sensitivity emerges in a different model that explicitly resolves mineralogical control on decomposition. These results support projections of strong carbon–climate feedbacks from northern soils5,6 and demonstrate a method for ESMs to capture this emergent behaviour.