PNNL

Abstract

The majority of the Earth’s terrestrial carbon (C) is stored in the soil. If anthropogenic warming stimulates the loss of this C into the atmosphere, it could drive additional planetary warming1–4. Despite evidence that warming enhances soil C fluxes to and from the soil5,6, the net global balance between these responses remains uncertain. Here we present a comprehensive analysis of warming-induced changes in soil carbon stocks by assembling data from 49 field experiments located across North America, Europe and Asia. We find that the effects of warming are contingent upon the size of the initial soil C stock, with considerable C losses occurring in high-latitude areas. By extrapolating this empirical relationship to the global scale, we provide estimates of soil C sensitivity that may help to constrain Earth System Model projections. Our empirical relationship suggests that global soil C stocks in the upper soil horizons will fall by 30 (± 30) to 203 (± 161) Pg C under 1 degree of warming, depending on the rate at which warming effects are realised. Under the conservative assumption that the soil C response to warming occurs within a year, a business-as-usual climate scenario would drive the loss of 55 (± 50) Pg C from the upper soil horizons by 2050. This value is ~12-17% of expected anthropogenic emissions over this period7,8. Despite the considerable uncertainty in our estimates, the direction of the global soil carbon response is consistent across all scenarios. This provides strong empirical support for the idea that rising temperatures will stimulate the net loss of soil C to the atmosphere, driving a positive land carbon-climate feedback that could accelerate climate change.