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Stratospheric Aerosol Injection
Stratospheric Aerosol Injection – or SAI – is an idea to create a thin, persistent layer of tiny particles in the upper atmosphere to reflect sunlight and cool the planet. How could it work and why is it being studied?
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Stratospheric Aerosol Injection – or SAI – is an idea to create a thin, persistent haze of tiny particles in the upper atmosphere to reflect sunlight and cool the planet. This idea was inspired by the cooling effects of powerful volcanic eruptions like Tambora(1) and Pinatubo(2).
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These eruptions were so powerful that their plumes reached the stratosphere, a stable, dry layer of the atmosphere(1,2). They each added millions of tons of tiny, reflective sulphate particles which spread out around the world reflecting a small fraction of incoming light and cooling the planet for a few years(1,2).
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Stratospheric Aerosol Injection aims to achieve a similar cooling effect.
Using high altitude jets, millions of tons of tiny particles would be released to the stratosphere every year to reflect light back to space(3,4). Many of the impacts of climate change are closely tied to temperature, and so by lowering temperatures, SAI could help reduce sea-level rise(5), extreme heat(6), and other climate risks.
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SAI might reduce climate change’s impact on rainfall overall, but it could affect regional rainfall patterns(7). It could also have side effects, such as delaying the slow recovery of the ozone hole(8) and adding to the acid rain problem(9).
SAI presents several questions:
- Would some regions be made worse off by SAI?
- What impact would SAI have on efforts to cut greenhouse gas emissions?
- Who would decide whether and how SAI should be used?
Decisions about SAI should be informed, which will require more research, and more discussion, by people and organizations across the world.
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Endnotes
- Kandlbauer J, Hopcroft PO, Valdes PJ, et al. Climate and carbon cycle response to the 1815 Tambora volcanic eruption. Journal of Geophysical Research Atmospheres 2013; 118: 12,497-12,507.
- Global Effects of Mount Pinatubo, https://earthobservatory.nasa.gov/images/1510/global-effects-of-mount-pinatubo (2001, accessed 21 November 2024).
- Smith W. The cost of stratospheric aerosol injection through 2100. Environmental Research Letters; 15. Epub ahead of print 1 November 2020. DOI: 10.1088/1748-9326/aba7e7.
- Lockley A, Macmartin D, Hunt H. An update on engineering issues concerning stratospheric aerosol injection for geoengineering. Environmental Research Communications; 2. Epub ahead of print 7 August 2020. DOI: 10.1088/2515-7620/aba944.
- Yue C, Jevrejeva S, Qu Y, et al. Thermosteric and dynamic sea level under solar geoengineering. NPJ Clim Atmos Sci; 6. Epub ahead of print 1 December 2023. DOI: 10.1038/s41612-023-00466-4.
- Ji D, Fang S, Curry CL, et al. Extreme temperature and precipitation response to solar dimming and stratospheric aerosol geoengineering. Atmos Chem Phys 2018; 18: 10133–10156.
- Irvine PJ, Keith DW. Halving warming with stratospheric aerosol geoengineering moderates policy-relevant climate hazards. Environmental Research Letters; 15. Epub ahead of print 1 April 2020. DOI: 10.1088/1748-9326/ab76de.
- Haywood J, Tilmes S, Keutsch F, et al. Chapter 6: Stratospheric Aerosol injection and its Potential Effect on the Stratospheric Ozone Layer. In: Scientific Assessment of Ozone Depletion 2022. 2022, pp. 325–375.
- Visioni D, Slessarev E, Macmartin DG, et al. What goes up must come down: Impacts of deposition in a sulfate geoengineering scenario. Environmental Research Letters; 15. Epub ahead of print 1 September 2020. DOI: 10.1088/1748-9326/ab94eb.
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