Thaw subsidence accelerates permafrost degradation

One of the major issues associated with degrading permafrost is thaw subsidence caused by the melting of ground ice. This process has great impacts on engineered structures, hydrological cycles, the carbon cycle, and energy processes under climate change. However, accurately representing thaw subsidence in permafrost dynamics still poses a significant challenge for Earth system models (ESMs). In this study, we used a moving-grid permafrost model (MGPM) incorporating heat transfer processes, the ground ice melting process, and thaw subsidence processes to project that the rates of increase in cumulative thaw subsidence will be 0.43 m/decade, 0.58 m/decade, and 0.77 m/decade under the SSP1-2.6, SSP4-6.0, and SSP5-8.5 scenarios, respectively. On average, accounting for thaw subsidence accelerates the complete degradation of permafrost by over 17 years across future scenarios with varying ground ice conditions. This mainly manifests in the marked acceleration of upward degradation of permafrost due to the warming of the upper boundary, which obstructs the upward transfer of geothermal energy from the lower boundary, creating a canopy effect. When thaw subsidence is accounted for, the initial energy consumed by ground ice melting increases substantially—absorbing 7% more energy on average—thereby accelerating permafrost thinning. Moreover, incorporating thaw subsidence leads to faster release of meltwater from ground ice and accelerated thawing of permafrost-stored carbon. By quantifying its effects, this study enhances understanding of permafrost degradation and its consequences. These findings underscore the need to integrate thaw subsidence into Earth System Models (ESMs) to improve permafrost simulations.