Comprehensive assessment of permafrost carbon emissions indicates need for urgent action to keep Paris Agreement temperature goals within reach

Abstract Rapid Arctic warming is thawing carbon-rich permafrost, releasing greenhouse gasses to the atmosphere and accelerating global climate change. Despite the importance of this feedback, permafrost-enabled global-scale models simulate only one mechanism of belowground carbon loss: the gradual, top-down thickening of the seasonally-thawed soil layer. This ignores abrupt permafrost thaw and intensifying fire regimes that result in combustion of soil carbon and fire-induced thaw. Here, we expand a compact Earth system model (OSCAR v3.0) to enable first-order estimates of the impacts of abrupt thaw and wildfire, together with gradual thaw, on remaining carbon budgets consistent with the temperature goals of the Paris Agreement. We find that remaining carbon budgets are reduced by up to 20% for 1.5°C, and up to 22% for 2.0°C. Ensuring that these substantial future emissions are accounted for when developing emissions reductions targets consistent with the Paris agreement presents a timely challenge for scientific and policy communities.