Seasonally Modulated Stratospheric Aerosol Geoengineering Alters the Climate Outcomes

By reflecting some incoming solar radiation, stratospheric aerosol intervention using SO₂ would reduce global mean temperature. Previous research has shown that multiple injection latitudes can be used to maintain not only global mean temperature, but also interhemispheric and equator-to-pole temperature gradients. However, the regional climate response depends not only on where the SO₂ is injected, but also on when. We show here that even with these same objectives and same choices of latitudes, injecting in only one season instead of continuously throughout the year results in significant differences in regional climate, for instance in the magnitude of precipitation changes over India. The differential outcomes highlight the potential for underlying trade-offs, with different choices regarding deployment leading to a different distribution of benefits or harms. This aspect of climate engineering should be considered in developing governance and emphasizes the need for a deeper understanding of the mechanisms underlying the regional responses.