Increase in physical and economic risks induced by permafrost thaw

Warming-induced greenhouse gas emissions from permafrost constitute a major uncertainty in assessments of Earth system stability, remaining carbon budgets, and the feasibility of long-term climate targets. While gradual permafrost thaw is represented in several complex Earth system models, abrupt thaw processes such as thermokarst development and active-layer detachment remain absent, despite their potential to generate rapid and substantial emissions. Here, we quantify the contribution of both gradual and abrupt permafrost thaw to CO₂ and CH₄ emissions and associated climate risks using the compact Earth system model OSCAR, extended with a newly implemented inventory-based module for abrupt permafrost thaw dynamics. Probabilistic projections of global temperature, sea-level rise, and direct economic damage costs are enabled across seven state-of-the-art scenarios from the Network for Greening the Financial System.

Our results show that permafrost carbon feedback introduces pronounced nonlinearities into climate outcomes. Risks associated with gradual thaw scale closely with global warming, whereas abrupt thaw exhibits complex, scenario-dependent effects that disproportionately influence upper-tail risks. These findings suggest that neglecting permafrost thaw may lead to systematic underestimation of tail risks. By explicitly linking permafrost thaw processes to climate risk metrics, this study contributes to reducing a key blind spot in climate‑impact assessments.