Stratospheric aerosol injection

Stratospheric aerosol injection is a proposed method of solar geoengineering (or solar radiation modification) to reduce global warming. This would introduce aerosols into the stratosphere to create a cooling effect via global dimming and increased albedo, which occurs naturally from volcanic winter.^[1] It appears that stratospheric aerosol injection, at a moderate intensity, could counter most changes to temperature and precipitation, take effect rapidly, have low direct implementation costs, and be reversible in its direct climatic effects.^[2] The Intergovernmental Panel on Climate Change concludes that it "is the most-researched [solar geoengineering] method that it could limit warming to below 1.5 °C (2.7 °F)."^[3] However, like other solar geoengineering approaches, stratospheric aerosol injection would do so imperfectly and other effects are possible,^[4] particularly if used in a suboptimal manner.^[5]

Various forms of sulfur have been shown to cool the planet after large volcanic eruptions.^[6] However, as of 2021, there has been little research and existing natural aerosols in the stratosphere are not well understood.^[7] So there is no leading candidate material. Alumina, calcite and salt are also under consideration.^[8][9] The leading proposed method of delivery is custom aircraft.^[10]