Permafrost dynamics in the Northern Hemisphere under future climate scenarios based on CMIP6.

Global warming is increasingly affecting permafrost in the Northern Hemisphere, with permafrost degradation being one of the most serious consequences of climate change on the cryosphere. Based on the CMIP6 soil temperature data from 15 different earth system models (ESMs) (ACCESS-CM2, ACCESS-ESM1-5, BCC-CSM2-MR, CanESM5, CESM2, CESM2-WACCM, EC-Earth3, FGOALS-f3-L, IPSL-CM6A-LR, MIROC6, MPI-ESM1-2-HR, MPI-ESM1-2-LR, MRI-ESM2-0, NorESM2-LM, NorESM2-MM), we analyzed the spatiotemporal variations of the permafrost area and active layer thickness (ALT) in the Northern Hemisphere under different future emission scenarios (SSP126, SSP245, SSP370, and SSP585), aiming to clarify the main environmental driving factors affecting the changes in ALT. Results showed significant discrepancies in the simulation capabilities of ALT across ESMs. Based on the analysis of the four optimal performance ESMs (MPI-ESM1-2-LR, ACCESS-ESM1-5, MPI-ESM1-2-HR, and BCC-CSM2-MR), we found that the reduction rate of permafrost area significantly accele-rated from 2015 to 2100 under high emission scenarios (SSP370, SSP585), and the rate of permafrost area decline under SSP585 scenario was eight times that of SSP126 scenario. The permafrost area would increase under SSP126 scenario, but it would continue to decrease under SSP245, SSP370, and SSP585 scenarios. ALT was projected to increase significantly under all four scenarios, with the annual increasing rate under SSP585 being 22 times higher than SSP126. Furthermore, we found that the end time of annual permafrost thawing would gradually change from September to November, leading to an extension of the thawing period. Key factors, such as air temperature, air humidity, vegetation leaf area index, snow cover, and wind speed showed positive effects on permafrost degradation in most regions, while soil moisture showed negative effect. Overall, future greenhouse gas emission controls would offer potential pathways to mitigate the risk of rapid permafrost degradation in the Northern Hemisphere.