Permafrost Response in Northern High-Latitude Regions to 1.5°C Warming and Overshoot Scenarios Achieved via Solar Radiation Modification

The thawing of carbon-rich northern high-latitude permafrost might unleash irreversible changes in the Earth's climate system. Previous studies have suggested that solar radiation modification (SRM) can significantly slow the degradation of permafrost, potentially restoring its extent and soil carbon stocks to levels comparable to those under equivalent global warming caused by greenhouse gas increases alone. However, this study identifies that the efficacy of SRM in mitigating permafrost degradation is contingent upon the warming trajectory and the timing of SRM intervention. Employing SRM to keep global warming at a maximum of 1.5°C can substantially reduce permafrost degradation; however, simulations suggest that by 2300, approximately half of the permafrost area reduction and one-third of the carbon losses expected under the high-emissions SSP5-8.5 scenario would still take place. By employing SRM to achieve a return to 1.5°C warming stabilization levels after a temperature overshoot, it is possible to effectively restore the permafrost area. However, the lost permafrost carbon cannot be regained. Additionally, the soil carbon within permafrost regions displays contrasting trends between the phases of overshoot and subsequent stabilization. Our simulations show that achieving the 1.5°C warming target after a 4°C temperature overshoot could necessitate up to 7% increase in SRM application due to permafrost carbon release. Moreover, perturbed parameter ensemble simulations indicate that the key parameter influencing the uncertainty of soil carbon losses in permafrost regions under 1.5°C warming and overshoot scenarios is distinct from that under the SSP5-8.5 scenario.