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

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023EF004191?af=R

Authors 

A. L. Morrison, E. A. Barnes, J. W. Hurrell

First published: 16 June 2024

https://doi.org/10.1029/2023EF004191

Abstract

Stratospheric aerosol injection (SAI) has been proposed as a potential method for mitigating risks and impacts associated with anthropogenic climate change. One such risk is widespread permafrost thaw and associated carbon release. While permafrost has been shown to stabilize under different SAI scenarios, natural variability may mask this forced response and make it difficult to detect if and when SAI is stabilizing permafrost. Here we use the 10-member ensemble from the ARISE-SAI-1.5 simulations to assess the spread in projected active layer depth and permafrost temperature across boreal permafrost soils and specifically in four peatland and Yedoma regions. The forced response in active layer depth and permafrost temperature quickly diverges between an SAI and non-SAI world, but individual ensemble members overlap for several years following SAI deployment. We find that, due to projected permafrost variability, it may take more than a decade of SAI deployment to detect the effects of SAI on permafrost temperature and almost 30 years to detect its effects on active layer depth. Not only does natural variability make it more difficult to detect SAI's influence, it could also affect the likelihood of reaching a permafrost tipping point. In some realizations, SAI fails to prevent a local tipping point that is also reached in a non-SAI world. Our results underscore the importance of accounting for natural variability in assessments of SAI's potential influence on the climate system.

Key Points

Projected natural variability in permafrost fields in peatland and Yedoma regions can mask forced response to stratospheric aerosol injection (SAI)

Effect of SAI on active layer and soil temperature is only detectable after more than a decade of aerosol deployment

Natural variability affects likelihood of reaching precursor to permafrost tipping point despite surface cooling effect of SAI

Plain Language Summary

Injecting highly reflective particles into the upper atmosphere, or stratospheric aerosol injection (SAI), is a proposed climate intervention method for deliberately stabilizing or cooling the Earth's temperature and preventing undesirable impacts of human-caused climate change, such as thawing permafrost. Permafrost can potentially release stored carbon into the atmosphere as carbon dioxide and methane that contributes to the greenhouse effect. Climate model simulations show that SAI could stabilize permafrost and prevent it from thawing, but that natural fluctuations in the Earth's climate may cause a wide range of outcomes for future permafrost thaw depth and soil temperature. We show that, due to these natural climate fluctuations, it may take 10–30 years of SAI to clearly see its influence on permafrost thaw depth and temperature. Certain conditions that lead to runaway thaw and soil carbon release (i.e., tipping points) may also occur even if SAI successfully stabilizes the Earth's globally averaged temperature. When weighing possible outcomes of proposed climate intervention strategies, it is important to consider the effects of natural climate fluctuations in assessing the pros and cons of different strategies.

Source: AGU