Response of Tipping Elements to Different Strategies of Stratospheric Aerosol Injection

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025EF006736

Authors: Mengying Zhao, Long Cao, Daniele Visioni, Douglas G. MacMartin

First published: 02 December 2025

https://doi.org/10.1029/2025EF006736

Abstract

Stratospheric aerosol injection (SAI) has been proposed as a complementary option to mitigate anthropogenic climate change risks. Using Community Earth System Model ensemble simulations, we assess the response of climate metrics relevant to a set of climate tipping elements in SAI scenarios targeting different temperature stabilization goals and for implementation at different latitudes. We analyze responses of tipping element metrics in simulations of a multi-objective SAI strategy that is designed to simultaneously stabilize global mean temperature (T0), interhemispheric temperature gradient (T1), and equator-to-pole temperature gradient (T2), as well as simulations of SAI strategies designed just to stabilize T0. We show that SAI strategies considered here would reduce the risks for many tipping elements, but may either increase or decrease the risk of Antarctic ice sheet collapse and Sahel greening, depending on the specifics of injection strategy. For the same 1.0°C temperature stabilization target, high-latitude injection would reduce the risk of northern cryosphere-related tipping elements more effectively, such as Greenland ice sheet, Barents winter sea ice, and boreal permafrost. Meanwhile, low-latitude injection would be more effective in stabilizing low-latitude biosphere-related tipping elements such as Amazon rainforest and coral reefs. The multi-objective SAI injection is more effective in reducing the risk of most high-latitude tipping elements than low-latitude injection, and is more effective in reducing the risk of most low-latitude tipping elements than high-latitude injection. Our study highlights the importance of careful consideration in the trade-offs between tipping element risk reduction and temperature pattern optimization in response to SAI strategies.

Plain Language Summary

Stratospheric Aerosol Injection (SAI) is a proposed method to cool the planet by releasing scattering particles into the upper atmosphere to reflect sunlight back to space. This climate intervention method would affect Earth's tipping elements, such as ice sheets and rainforests, which may exhibit abrupt or irreversible changes upon reaching critical thresholds. In this study, we use an Earth system model to analyze SAI's impact on climate metrics that are indicative of the risks of certain tipping elements crossing their thresholds. Our results show that compared to the scenario of increasing greenhouse gas emissions without artificial climate intervention, SAI could reduce the risk for many tipping elements. Deploying SAI at high latitudes is more effective at protecting northern cryosphere-related tipping elements such as Greenland ice sheet, Barents winter sea ice, and boreal permafrost. On the other hand, deploying SAI at low latitudes is more effective at protecting tipping elements such as Amazon rainforest and coral reefs. SAI targeting multiple temperature objectives including global mean temperature, equator-to-pole and interhemispheric temperature gradient, may not be the optimal approach for reducing some tipping element risks. Designing SAI strategies therefore requires carefully weighing the goal of stabilizing temperature pattern against minimizing tipping element risks.

Key Points

We analyze CESM2-simulated response of tipping element metrics to different strategies of Stratospheric aerosol injection (SAI)

SAI could reduce risks for many but not all tipping elements

Multi-objective injection is not the most effective strategy for many tipping elements

Source: AGU