Wildfires accelerate permafrost area loss via reducing soil organic matter

The stability of permafrost is regulated by the thermal insulating properties of soil organic carbon (SOC). However, intensifying wildfires across the Arctic and boreal regions are removing the protective soil organic layer, which may trigger positive feedback that accelerates thaw, yet the pan-Arctic scale of this threat remains unknown. Here we present a data-driven framework, aiming to address two questions: i) what is the net SOC loss due to fire across the northern permafrost zones, accounting for immediate SOC combustion and post-fire recovery, and ii) to what extent does this fire-induced SOC reduction accelerate permafrost degradation. To achieve this, we developed a bookkeeping model parameterized by SOC data from over 1,000 paired burned and unburned sites across diverse ecosystems to simulate fire-induced SOC dynamics, and a permafrost probability model based on air temperature and SOC content, advancing earlier temperature-only approaches. Driven by CMIP6 climate and burned area projections, we find that under SSP1-2.6, fire-induced SOC loss, considering both combustion and post-fire recovery, reaches 15.0±3.6 Pg C by 2100. This SOC reduction diminishes the soil’s insulative capacity, leading to an additional permafrost loss of 2.7±0.7 million hectares. This impact is most pronounced under low-emission scenarios, where permafrost exists in a climatically marginal state; here, every 1 km² of increased burned area causes 0.19 km² of additional permafrost loss. Under SSP5-8.5, fire-driven permafrost loss is less pronounced as rapid atmospheric warming is the predominant driver. Our findings reveal that wildfire is an efficient agent of permafrost thaw, highlighting the urgent need to incorporate dynamic fire-SOC-thermal interactions into ESMs to avoid underestimation of future permafrost degradation.