Spray aerosols to cool the atmosphere?

Article by Isabel Key and Yannis Wells.

Greenhouse gases, such as CO2, warm the planet [1]. Is there such thing as an “anti-greenhouse gas”? Yes – aerosols [3,11]! These are ‘suspensions’ of small particles in the atmosphere – they are not gases [14]. Most aerosols reflect sunlight and send it back into space, cooling the atmosphere (swipe for a diagram!) [13,14]*.

Some scientists have suggested injecting aerosols called sulfates into the atmosphere [19] by shooting particles with guns or hoses, or emptying particles out of an airplane [15]. Aerosol injection could also be used on a local (rather than global) scale e.g. to cause more cooling over the poles [19].

CO2 stays in the atmosphere for centuries to millennia [9]. Therefore, if we want to stop temperatures from rising we can’t just reduce emissions – we also need to either remove greenhouse gases or use a method like aerosol injection to cool the planet [9,19]. Aerosol injection could cool the Earth by 0.3°C for $36 billion spent over 15 years [3]. This is much cheaper than removing CO2 from the air [2,9].

However, there are many risks associated with aerosol injection [1]:

We don’t fully understand how it would affect regional climates [16] but it might cause droughts in India, South Asia, and parts of Africa [1]. The sulfate aerosols could cause acid rain [10], and aerosol injection would not solve ocean acidification: CO2 would continue to dissolve in the ocean [6,19]. Furthermore, aerosols would have to be continually added to the atmosphere for centuries (until CO2 added by humans has left the atmosphere, e.g. by being taken up by the ocean) [19,22].

Despite this, we could need aerosol injection in addition to radically reducing emissions and adapting to the consequences of climate change [7,8,18,21]. It is a topic deserving further research, so that we know how to do it safely if we have no better option [7,9].

*There are many different types of aerosols – you may have heard of CFCs, which damage the ozone layer (which protects us from damaging radiation from the Sun) [12,20].

References

[1] https://climate.nasa.gov/causes/

[2] https://www.sciencedirect.com/science/article/pii/S2542435118302253

[3] https://iopscience.iop.org/article/10.1088/1748-9326/aae98d/meta
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016EF000465%4010.1002/%28ISSN%292328-4277.GEOENGIN1 See: Table 1 and 5

[6] https://www.annualreviews.org/doi/pdf/10.1146/annurev.marine.010908.163834?casa_token=epfNZr73XwcAAAAA:44k564yi1l-OImwihm8tgSH3rfJp1ikG4MHYzcjFQod4MPd7d4ZYKUMIOuJGJ2vHxOIcp_JDsV_BMw

[7] https://www.ametsoc.org/index.cfm/ams/about-ams/ams-statements/statements-of-the-ams-in-force/geoengineering-the-climate-system/

[8] https://iopscience.iop.org/article/10.1088/1748-9326/11/5/054009/pdf

[9] https://www.sciencedirect.com/science/article/abs/pii/S0016328717301131

[10] https://search.proquest.com/docview/198512444?pq-origsite=gscholar

[11] http://www.jsg.utexas.edu/news/2008/08/the-anti-greenhouse-gas-climate-scientist-evaluates-geoengineering-solution-to-climate-change/

[12] https://www.britannica.com/science/chlorofluorocarbon

[13] https://earthobservatory.nasa.gov/features/Aerosols

[14] https://www.sciencedaily.com/releases/2016/04/160401145037.htm

[15] http://www.geoengineeringmonitor.org/2018/06/stratospheric_aerosol_injection/

[16] https://eos.org/research-spotlights/tailoring-aerosol-injections-to-achieve-desired-climate-effects

[17] https://www.cbsnews.com/news/geoengineering-treatment-stratospheric-aerosol-injection-climate-change-study-today-2018-11-23/

[18] https://www.theguardian.com/environment/2018/oct/08/geoengineering-global-warming-ipcc

[19] https://www.pnas.org/content/116/4/1089

[20] https://www.nationalgeographic.org/encyclopedia/ozone-layer/

[21] https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter07_FINAL-1.pdf

[22] https://www.pnas.org/content/106/6/1704

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