Northern high-latitude permafrost and terrestrial carbon response to solar geoengineering

Abstract

Abstract. The northern high-latitude permafrost contains almost twice the carbon content of the atmosphere, and it is widely considered as a non-linear and tipping element in the Earth's climate system under global warming. Solar geoengineering is a means of mitigating temperature rise and reduce some of the associated climate impacts by increasing the planetary albedo, including permafrost thaw. We analyze the permafrost response as simulated by five earth system models (ESMs) under four future scenarios; two solar geoengineering scenarios (G6solar and G6sulfur) restore the global temperature from the high emission scenario (ssp585) levels to the moderate mitigation scenario (ssp245) levels via solar dimming and stratospheric aerosol injection. G6solar and G6sulfur nearly restore the northern high-latitude permafrost area from ssp585 levels to those under ssp245. But deeper active layer thickness and more exposed unfrozen soil organic carbon are produced due to robust residual high-latitude warming, especially over Eurasia. However, G6solar and G6sulfur accumulate more soil carbon over the northern high-latitude permafrost region due to enhanced CO2 fertilization effects relative to ssp245 and weakened heterotrophic respiration relative to ssp585. The asynchronous changes in soil carbon inputs and soil carbon decomposition directly result from decoupling of temperature and atmospheric CO2 concentration under solar geoengineering. The permafrost ecosystem remains a carbon sink throughout this century under all four scenarios, and solar geoengineering can delay the transition of northern high-latitude permafrost ecosystem from carbon sink to carbon source.