Permafrost response and feedback under temperature stabilization and overshoot scenarios with different global warming levels

Abstract. Permafrost regions in the northern high latitudes face significant degradation risks under global warming and threaten the achievement of global climate goals. This study explores nonlinear permafrost response and feedback under temperature stabilization (SWL) and overshoot (OS) scenarios with various global warming levels (GWLs). Under the 1.5 °C and 2 °C SWL scenarios, permafrost area loss is 4.5 [4.4 to 4.7] million km² and 6.5 [6.4 to 6.8] million km² respectively. In the OS scenarios, permafrost area can recover effectively, with an additional loss of only 0.3~1.1 million km² compared to the 1.5 °C SWL scenario. However, permafrost carbon loss in the OS scenarios is irreversible, with 9~44 PgC less loss compared to the SWL scenarios. Both SWL and OS scenarios show that additional warming due to permafrost carbon feedback rises with higher GWLs, and the most substantial permafrost carbon feedback in OS scenarios is anticipated to take place during the cooling phase. In the OS scenarios, the proportion of additional permafrost area loss due to permafrost carbon feedback increases with higher GWLs, reaching 6~12 % of total permafrost degradation. In contrast, under the SWL and SSP5-8.5 scenarios, additional permafrost area loss generally decreases as GWLs rise. The additional permafrost area loss due to permafrost carbon feedback is influenced by both the magnitude of additional warming and the sensitivity of permafrost area to global warming (SPAW). The maximal SPAW falling between 1.5 °C and 2 °C has significant implications for achieving the global warming levels of the Paris Agreement.