High‐Latitude Stratospheric Aerosol Geoengineering Can Be More Effective if Injection Is Limited to Spring.

Stratospheric aerosol geoengineering focused on the Arctic could substantially reduce local and worldwide impacts of anthropogenic global warming. Because the Arctic receives little sunlight during the winter, stratospheric aerosols present in the winter at high latitudes have little impact on the climate, whereas stratospheric aerosols present during the summer achieve larger changes in radiative forcing. Injecting SO2 in the spring leads to peak aerosol optical depth (AOD) in the summer. We demonstrate that spring injection produces approximately twice as much summer AOD as year‐round injection and restores approximately twice as much September sea ice, resulting in less increase in stratospheric sulfur burden, stratospheric heating, and stratospheric ozone depletion per unit of sea ice restored. We also find that differences in AOD between different seasonal injection strategies are small compared to the difference between annual and spring injection. Plain Language Summary: Scattering small particles called aerosols into the sky, "geoengineering", could reflect a small amount of sunlight in order to combat global warming. Doing this near the Arctic could help stop sea ice from melting, which would help preserve the Arctic climate. Our study shows that, for Arctic geoengineering, scattering particles in the spring is most efficient because the particles will be present throughout the summer, and the Arctic receives the most sunlight in the summer. Therefore, spring Arctic geoengineering could accomplish the same goals as year‐round Arctic geoengineering, but with fewer particles and thus fewer negative side‐effects. Key Points: Arctic focused stratospheric aerosol injection (SAI) concentrated in spring produces peak aerosol optical depth (AOD) in summer and therefore reflects sunlight more efficiently than year round SAISpring injection at 60°N restores twice as much September sea ice per unit of injection as year round injection at the same latitudeLimiting Arctic injection to spring also results in less ozone loss and stratospheric heating per unit of September sea ice recovered [ABSTRACT FROM AUTHOR]