Introducing a Comprehensive Set of Stratospheric Aerosol Geoengineering Strategies

Stratospheric aerosol geoengineering, as a design problem, comes with a wide range of possible design choices, such as where and when to inject. Different injection strategies can yield different climate responses. Making informed future decisions regarding stratospheric aerosol injection (SAI) requires an understanding of the range of possible climate outcomes. Yet to date, there has not been a systematic exploration of a comprehensive set of SAI strategies. This limits the ability to determine what effects are robust and what depend on specific injection choices.

In this study, we introduce four hemispherically symmetric injection strategies, all of which are designed to maintain a desired global mean temperature: annual SO2 injection at the equator, annual injection of equal amounts of SO2 at 15N and 15S, annual injection of equal amounts of SO2 at 30N and 30S, and spring injection of equal amounts of SO2 at 60N and 60S.

We simulate these strategies in the CESM2(WACCM6) Earth System Model and compare the simulated surface climate responses to each of these SAI strategies, including changes in surface air temperature, precipitation minus evaporation over land, the position of Intertropical Convergence Zone (ITCZ), and Arctic sea ice extent. We further compare these four hemispherically symmetric SAI strategies with a multi-objective strategy that injects SO2 at four latitudes in the tropical and subtropical regions in order to maintain not only the global mean surface temperature but also its large-scale horizontal gradients. This new set of SAI strategies contribute to the future work on analyzing the trade-offs between achieving different climate objectives, and help evaluate the fundamental limits of SAI.