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Despite offsetting global mean surface temperature, various studies demonstrated that Stratospheric Aerosol Injection (SAI) could influence the recovery of stratospheric ozone and have important impacts on stratospheric and tropospheric circulation, thereby potentially playing an important role in modulating regional and seasonal climate variability. However, so far most of the assessments of such an approach have come from climate model simulations in which SO2 is injected only in a single location or a set of locations. Here we use CESM2-WACCM6 SAI simulations under a comprehensive set of SAI strategies achieving the same global mean surface temperature with different locations and/or timing of injections: an equatorial injection, an annual injection of equal amounts of SO2 at 15N and 15S, an annual injection of equal amounts of SO2 at 30N and 30S, and a polar strategy injecting SO2 at 60N and 60S only in spring in each hemisphere. We demonstrate that despite achieving the same global mean surface temperature, the different strategies result in contrastingly different impacts on stratospheric temperatures and circulation, thereby leading to different impacts on Northern Hemispheric polar vortex and, thus, winter mid- and high latitude surface climate, as well as leading to important differences in the future evolution of stratospheric ozone throughout the globe. Overall, the results contribute to an increased understanding of the underlying physical processes as well as lay ground for identifying an optimal SAI strategy that could form a basis of a future multi-model assessment., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The Geoengineering Model Intercomparison Project (GeoMIP) is a coordinating framework, started in 2010, that includes a series of standardized climate model experiments aimed at understanding the physical processes and projected impacts of solar geoengineering (also known as “climate intervention”). Numerous experiments have been conducted, and several more have been proposed as “testbed” experiments, spanning a variety of geoengineering techniques aimed at modifying the planetary radiation budget: stratospheric aerosol injection, marine cloud brightening, surface albedo modification, cirrus cloud thinning and sunshade mirrors. To date, over 125 studies have been published that used results from GeoMIP simulations.Here we provide an introduction to GeoMIP and its experiments. We discuss the knowledge that GeoMIP has contributed to the field of geoengineering research and climate scienc: what have we learned in terms of inter-model differences, robustness of the projected outcomes for specific methods and future areas of model development that would for the future. We also offer multiple examples of cases where GeoMIP experiments were fundamental for international assessments.We provide a critical assessment of GeoMIP with an eye toward future priorities in simulation design and analysis. We discuss the next set of experiments we are working on, in light of future Climate Model Intercomparison Project scenarios and activities, highlighting areas of collaborations with other international projects and intercomparisons. We outline a series of criteria that should guide the development of future GeoMIP experiments and make them relevant to its participants and the broader community, centered around plausibility, policy relevance, scientific relevance and reproducibility., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)