Potential Non‐Linearities in the High Latitude Circulation and Ozone Response to Stratospheric Aerosol Injection.

The impacts of Stratospheric Aerosol Injection (SAI) on the atmosphere and surface climate depend on when and where the sulfate aerosol precursors are injected, as well as on how much surface cooling is to be achieved. We use a set of CESM2(WACCM6) SAI simulations achieving three different levels of global mean surface cooling and demonstrate that unlike some direct surface climate impacts driven by the reflection of solar radiation by sulfate aerosols, the SAI‐induced changes in the high latitude circulation and ozone are more complex and could be non‐linear. This manifests in our simulations by disproportionally larger Antarctic springtime ozone loss, significantly larger intra‐ensemble spread of the Arctic stratospheric jet and ozone responses, and non‐linear impacts on the extratropical modes of surface climate variability under the strongest‐cooling SAI scenario compared to the weakest one. These potential non‐linearities may add to uncertainties in projections of regional surface impacts under SAI. Plain Language Summary: The injection of reflective aerosols, or their precursors, into the lower stratosphere (Stratospheric Aerosol Injection, SAI) has been proposed as a temporary measure to offset some of the adverse impacts of climate change whilst atmospheric concentrations of greenhouses are being stabilized and, ultimately, reduced. The impacts of SAI on the atmosphere and surface climate would depend on when and where the sulfate aerosol precursors are injected, as well as on how much surface cooling is to be achieved. Here we analyze SAI impacts on stratospheric climate and ozone in a set of Earth system model simulations under varying magnitudes of the SAI‐induced global mean cooling. We demonstrate that unlike some of the direct surface climate impacts from the reflection of solar radiation by sulfate aerosols, the SAI‐induced changes in stratospheric circulation, chemistry and climate are more complex, with the model simulations pointing toward more non‐linear behavior of the high latitude circulation and ozone under higher SAI scenarios. These potential non‐linearities may add to uncertainties in projections of regional surface impacts under SAI. Key Points: Impacts of Stratospheric Aerosol Injection (SAI) depend on how much surface cooling is to be achievedHigh latitude circulation, ozone and modes of extratropical variability can vary non‐linearly with the SAI‐induced global surface coolingThese potential non‐linearities may add to uncertainties in projections of regional surface impacts under SAI [ABSTRACT FROM AUTHOR]