PInc-PanTher estimates of Arctic permafrost soil carbon under the GeoMIP G6solar and G6sulfur experiments

Abstract. Circum-Arctic permafrost represents a tipping element for the Earth's climate system that must be maintained to avoid catastrophic climate change. Solar geoengineering (SG) has the potential to slow Arctic temperature rise by increasing planetary albedo, but could also reduce tundra productivity. Here, we improve the data-constrained PInc-PanTher model of permafrost carbon storage by including estimates of plant productivity and rhizosphere priming on soil carbon. Six earth system models are used to drive the model, running two SG schemes (G6solar and G6sulfur), and scenarios with substantive (SSP2-4.5) and no (SSP5-8.5) mitigation efforts. By 2100, simulations indicate that the permafrost area is expected to decrease by 9.2±0.4 (mean ± standard error), 5.6±0.4, 5.8±0.3, and 6.1±0.4 million km² and soil carbon loss will be 81±8, 47±6, 37±11, and 43±9 Pg under SSP5-8.5, SSP2-4.5, G6solar and G6sulfur, respectively. Uncertainties in permafrost soil C loss estimates arise mainly from changes in vegetation productivity due to climate warming and CO₂ fertilization. The increased input flux from vegetation to soil raises, while the priming effects of root exudates lowers soil C storage conservation, with the net effect mitigating soil C loss. Despite model differences, the protective effects of the G6solar and G6sulfur experiments on permafrost area and soil carbon storage are consistent and significant at the 95 % level for all six ESM. SG mitigates ~1/3 of permafrost area loss and halves carbon loss for SSP5-8.5, averting about $20 trillion in economic losses by 2100 and might provide a sustainable income stream for the Arctic population.