Climate intervention: effects of stratospheric aerosol injection on southern hemisphere extratropical cyclones

Abstract

Since the long residence time of greenhouse gases in the atmosphere limits the immediate effectiveness of traditional mitigation techniques, Climate Intervention (CI) approaches, specifically Stratospheric Aerosol Injection (SAI), emerge as potential strategies to reduce global warming. However, the impacts of SAI on components of the climate system, particularly on extratropical cyclones (ETCs) in the Southern Hemisphere, remain poorly understood, despite the high vulnerability of coastal regions to these systems. This study aimed to fill this gap by assessing the impacts of SAI on ETCs climatology, and their associated precipitation and winds, focusing on subdomains of South America, Southern Africa, and Australia. To this end, climate projections from the GeoMIP, GLENS, and ARISE-SAI international modeling projects were used, comparing scenarios with and without the application of SAI. The results indicate that, although the frequency of cyclones shows a decreasing trend in both future scenarios, the reduction is statistically less pronounced under SAI scenarios. Crucially, while unrestricted global warming (without SAI) projects an intensification of cyclones (lower central pressures), the implementation of SAI reduces this effect, keeping the intensity of the systems closer to that of the present climate. Regarding the associated impacts, it was observed that SAI induces a general weakening in precipitation and wind intensity at 10 meters generated by cyclones compared to scenarios without intervention. Consequently, the percentage contribution of cyclones to annual precipitation and wind totals tends to decrease from the near to the distant future under the influence of SAI, suggesting that this technique acts by bringing the dynamic and thermodynamic characteristics of cyclones closer to historical reference conditions. These findings highlight the problem that, although SAI is effective in mitigating the intensity of cyclones, it does not restore the climate to a state similar to the reference period, requiring assessments of potential risks and side effects. Thus, the implementation of intervention strategies requires caution and robust scientific research. Future studies need to improve high-resolution modeling and possible alternative strategies, as well as integrated research on other tipping points. Above all, there is an urgent need to include the Global South contexts in the risk assessments and governance of these technologies.