A Risk-Risk Assessment of Climate Extremes: Comparing Greenhouse Gas Warming and Stratospheric Aerosol Injection in UKESM1

[Geoengineering News]

https://doi.org/10.1029/2024EF005810

Authors: Alice F. Wells, James M. Haywood

First published: 16 October 2025

https://doi.org/10.1029/2024EF005810

Abstract

This study investigates the potential of Stratospheric Aerosol Injection (SAI), a solar climate intervention strategy, to mitigate climate extremes driven by greenhouse gas (GHG) emissions, comparing its effects to those of GHG-induced warming under the SSP5-8.5 scenario. Using the UKESM1 climate model and the GeoMIP G6controller scenario, we examine extreme temperature, precipitation, and fire risk indices in a risk-risk framework. The multi-latitude G6controller strategy, an improvement on the equatorial injection strategy G6sulfur, reduces global mean temperature from SSP5-8.5 to SSP2-4.5, significantly reducing temperature and precipitation extremes. Results show that G6controller effectively reduces temperature extremes relative to SSP5-8.5, especially in populated areas like Europe and South America, and reduces fire risk in high-risk areas, such as South America and southern Africa. While both scenarios project broad precipitation increases, G6controller moderates these without introducing new drying relative to SSP5-8.5, particularly in Southeast Asia. This study highlights G6controller's potential to lessen the magnitude of extreme climate events, offering insights into SAI's regional efficacy and highlighting the trade-offs between GHG warming with and without solar climate intervention.

Plain Language Summary

This study looks at how injecting reflective particles into the middle atmosphere, a process called Stratospheric Aerosol Injection (SAI), might help reduce the severe impacts of climate change, like heatwaves, heavy rainfall, and wildfires. It compares two future scenarios: one where greenhouse gas (GHG) emissions continue to rise and another where SAI is used to cool the planet. The results show that SAI can significantly reduce extreme heat and wildfire risks in many regions while also lessening the intensity of heavy rains. However, the strategy doesn't work equally well everywhere and comes with trade-offs. This research provides valuable insights for understanding how SAI could help manage climate risks in the future while emphasizing the continued importance of cutting GHG emissions.

Key Points

This study compares the impacts on extreme events under climate change with and without a multi-latitude Stratospheric Aerosol Injection strategy in UKESM1

G6controller reduces extreme heat relative to GHG warming, particularly in populated regions, reducing warming trends by nearly half

Fire danger days decrease under G6controller compared to SSP5-8.5, mitigating wildfire risks by reducing precipitation changes

Source: AGU