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

Abstract

Abstract. The northern-high-latitude permafrost contains almost twice the carbon content of the atmosphere, and it is widely considered to be 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 reduces some of the associated climate impacts by increasing the planetary albedo; the permafrost thaw is expected to be moderated under slower temperature rise. We analyze the permafrost response as simulated by five fully coupled earth system models (ESMs) and one offline land surface model under four future scenarios; two solar geoengineering scenarios (G6solar and G6sulfur) based on the high-emission scenario (ssp585) restore the global temperature from the ssp585 levels to the moderate-mitigation scenario (ssp245) levels via solar dimming and stratospheric aerosol injection. G6solar and G6sulfur can slow the northern-high-latitude permafrost degradation but cannot restore the permafrost states from ssp585 to those under ssp245. G6solar and G6sulfur tend to produce a deeper active layer than ssp245 and expose more thawed soil organic carbon (SOC) due to robust residual high-latitude warming, especially over northern Eurasia. G6solar and G6sulfur preserve more SOC of 4.6 ± 4.6 and 3.4 ± 4.8 Pg C (coupled ESM simulations) or 16.4 ± 4.7 and 12.3 ± 7.9 Pg C (offline land surface model simulations), respectively, than ssp585 in the northern near-surface permafrost region. The turnover times of SOC decline slower under G6solar and G6sulfur than ssp585 but faster than ssp245. The permafrost carbon–climate feedback is expected to be weaker under solar geoengineering.

Solar Geoengineering in the Polar Regions: A Review

“…There is limited direct modeling of permafrost changes under SAI, but in all cases, SAI is indeed found to reduce GHG emissions from permafrost degradation during its period of deployment (Chen et al., 2023; Chen et al., 2020; Jiang et al., 2019; H. Lee et al., 2019; W. R. Lee et al., 2023; Liu et al., 2023). Two recent multi‐model studies assessed the permafrost response under the G6sulfur SAI scenario (Chen et al., 2023; Liu et al., 2023). SAI is found to offset a large fraction of the permafrost carbon loss under SSP5‐8.5 (Chen et al., 2023; Liu et al., 2023).…”

“…SAI reduces mean annual surface temperatures in permafrost regions and so would be expected to reduce the loss of permafrost. There is limited direct modeling of permafrost changes under SAI, but in all cases, SAI is indeed found to reduce GHG emissions from permafrost degradation during its period of deployment (Chen et al., 2023; Chen et al., 2020; Jiang et al., 2019; H. Lee et al., 2019; W. R. Lee et al., 2023; Liu et al., 2023). Two recent multi‐model studies assessed the permafrost response under the G6sulfur SAI scenario (Chen et al., 2023; Liu et al., 2023).…”

“…Lee et al, 2019; W. R. Lee et al, 2023;Liu et al, 2023). Two recent multi-model studies assessed the permafrost response under the G6sulfur SAI scenario (Chen et al, 2023;Liu et al, 2023). SAI is found to offset a large fraction of the permafrost carbon loss under SSP5-8.5 (Chen et al, 2023;Liu et al, 2023).…”

“…Two recent multi-model studies assessed the permafrost response under the G6sulfur SAI scenario (Chen et al, 2023;Liu et al, 2023). SAI is found to offset a large fraction of the permafrost carbon loss under SSP5-8.5 (Chen et al, 2023;Liu et al, 2023). However, Chen et al (2023) show that the winter-time Northern Eurasian warming under this scenario described in Section 3.2 raises annual mean soil temperatures and prevents a full restoration of permafrost extent to that of the target scenario; 39% of baseline permafrost extent is retained under G6sulfur, as compared to 45% under the target scenario SSP2-4.5 (Chen et al, 2023).…”

“…However, Chen et al. (2023) show that the winter‐time Northern Eurasian warming under this scenario described in Section 3.2 raises annual mean soil temperatures and prevents a full restoration of permafrost extent to that of the target scenario; 39% of baseline permafrost extent is retained under G6sulfur, as compared to 45% under the target scenario SSP2‐4.5 (Chen et al., 2023). These findings are broadly in line with the only previous multi‐model assessment of permafrost response to SAI (Chen et al., 2020), which found that in the ensemble mean of seven earth system models running the GeoMIP SAI scenario G4, which injects less aerosols than are required to fully offset warming, cumulative CO 2 emissions from permafrost melting by 2070 are halved under the geoengineering scenario G4 relative to RCP4.5.…”