Stratospheric Aerosol Injection to Stabilize Northern Hemisphere Terrestrial Permafrost Under the ARISE‐SAI‐1.5 Scenario

Abstract

Permafrost, or ground that is continuously frozen for at least 2 years, contains vast stores of organic soil carbon. Stratospheric aerosol injection (SAI) may prevent tipping points that lead to widespread permafrost thaw and carbon release by cooling surface and soil temperatures, but it is unclear if or when permafrost could stabilize after SAI deployment. Here we use output from the ARISE‐SAI‐1.5 simulations to assess how permafrost may respond to a specific SAI strategy that maintains global mean surface temperature to 1.5°C above pre‐industrial levels. Permafrost responses under SAI are compared to responses under the control SSP2‐4.5 emissions scenario. We show that the rate of boreal permafrost thaw slows under SAI but does not fully stop, likely due to deep permafrost thaw processes that are resistant to surface temperatures changes. In both the ARISE‐SAI‐1.5 and SSP2‐4.5 simulations, permafrost completely thaws and disappears along the southern edge of the permafrost area by 2069, indicating that some permafrost loss may be inevitable even if SAI successfully stabilizes global mean surface temperatures. SAI does prevent a potential local tipping point (talik formation) in roughly 1 million km2 of permafrost. Most of the talik prevention occurs in permafrost peatlands. Thus, a more aggressive SAI strategy than that of ARISE‐SAI‐1.5 is likely required to prevent all future projected permafrost thaw.

Natural Variability Can Mask Forced Permafrost Response to Stratospheric Aerosol Injection in the ARISE‐SAI‐1.5 Simulations

“…Lee et al, 2019;W. Lee et al, 2023;Liu et al, 2023;Morrison et al, 2024), though to our knowledge this is the first work to assess the extent to which natural variability may mask the forced permafrost response to SAI. Earth's Future…”

“…Lee et al, 2019;W. Lee et al, 2023;Liu et al, 2023;Morrison et al, 2024). The thawing of permafrost, or ground that is consistently frozen for at least two consecutive years, is a particular area of concern because of the carbon stored in permafrost soils.…”

“…Lee et al, 2019;W. Lee et al, 2023) and prevent talik formation (Morrison et al, 2024) in the forced response. In a region as sensitive to temperature shifts as the Arctic, however, natural variability may lead to permafrost thaw or talik formation even if SAI successfully stabilizes global mean surface temperatures, thereby masking the forced response to SAI.…”