Solar Radiation Modification Reduces Soil Carbon Exposure to Decomposition in Northern Circumpolar Permafrost

Abstract:

The Northern Circumpolar permafrost contains large amounts of soil organic carbon (SOC) with an estimation of about 867 Pg C in depth of 0~3 m based on NCSCDv2 dataset. In the late 21st century, near surface temperature in permafrost area is expected to exceed well beyond 0℃ for the high forcing scenario SSP585 and thaws large volume of the permafrost, then accelerate the climate warming. Solar Radiation Modification (SRM) is a geoengineering method which deliberately to mitigate the climate warming. It is unknown how much and to what extent the SRM can slow down the northern high-latitude permafrost thawing and the exposure of permafrost SOC to microbial decomposition. Here we analyze GeoMIP6 simulations by four CMIP6 models to study how the northern high-latitude permafrost response under G6 geoengineering scenario and SSP245 and SSP585 scenarios. The G6 scenario is designed to reduce forcing from high forcing scenario SSP585 to medium forcing scenario SSP245. In contrast to SSP585, the annual mean surface air temperature in northern high-latitude permafrost region remains below 0℃ for G6, in which 16%-57% of permafrost remains in frozen condition. The northern high-latitude permafrost still serves as a net carbon sink in the 21th century even for SSP585, as vegetation carbon uptake counteracts carbon losses from soil microbial decomposition. Persistent warming exposes more permafrost SOC to decomposition. For the upper 3 m soil carbon in global, the permafrost region accounts for up to 40% by 2100 for SSP585. This proportion drops to 26%-28% for G6, and it is similar to SSP245. G6 reduces significant amount of SOC vulnerable to decomposition.