Strong Increase of Thawing of Subsea Permafrost in the 22nd Century Caused by Anthropogenic Climate Change

Most Earth System Models (ESMs) neglect climate feedbacks arising from carbon release from thawing permafrost, especially from thawing of subsea permafrost (SSPF). To assess the fate of SSPF in the next 1000 years, we implemented SSPF into JSBACH, the land component of the Max Planck Institute Earth System Model (MPI-ESM). This is the first implementation of SSPF processes in an ESM-component. We investigate three extended scenarios from the 6th phase of the Coupled Model Intercomparison Project (CMIP6). In the 21 st century only small differences are found among the scenarios, but in the upper-end emission scenario SSP5-8.5, especially in the 22 nd century SSPF ice melting is more than 15 times faster than in the preindustrial period. In this scenario about 35% of total SSPF volume and 34% of SSPF area is lost by year 3000 due to climatic changes. In the more moderate scenarios, the melting rate maximally exceeds that of preindustrial times by a factor of 4 and the climate change induced SSPF loss (volume and area) by year 3000 does not exceed 14%. Our results suggest that the rate of melting of SSPF ice is related to the length of the local open water season, and thus that the easily observable sea ice concentration may be used as a proxy for the change of SSPF.