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Our planet continues to heat up. 2023 was declared the hottest year ever recorded, overtaking the previous warmest year, 2016, by a significant margin. It's a sobering statistic, and one that's put the spotlight on one of the world's more niche climate cooling solutions, Solar Radiation Management, or SRM. SRM works on the principle that the Earth can be cooled by reflecting some of the sun's rays back into space.
SRM techniques range from putting giant mirrors into orbit to increasing the reflectivity of low-lying clouds over parts of the ocean. While still theoretical, apart from some small-scale experiments, the best researched and modelled SRM involves injecting sulphur dioxide into the stratosphere using planes or balloons. This form of SRM looks to replicate the cooling effect of major volcanic eruptions.
When Mount Pinatubo erupted in the Philippines in 1991 it blasted around 17mn tonnes of sulphur dioxide into the atmosphere. Climatologists estimated that global temperatures dropped by about half a degree Celsius over the following year as sulphate particles from the eruption reflected some sunlight back into space. In 2023, both the European Commission and the White House released reports calling for more research into SRM.
In the same year the UN Environment Programme described the technology as the only way to cool the planet in the short-term. But critics warn that we know far too little about the side-effects of attempting such cooling on a planetary scale. Some scientists argue it might change the colour of the sky to a milky white. Others suggest it might have unpredictable effects on weather patterns across the globe, and could potentially worsen extreme weather events such as droughts and monsoons in some regions.
They claim that it could weaken the stratospheric ozone layer that protects us from ultraviolet radiation. Also, it wouldn't do anything to fix other CO2-related problems, such as ocean acidification. A major concern is of nations acting unilaterally with little or no consideration of the broader global impacts of SRM. The costs of aerosol injection could run into tens of billions of dollars per year per one degree Celsius of cooling. That's not cheap, but easily affordable for a single big economy or a collection of smaller ones.
As yet, no framework exists for international co-operation on SRM. But perhaps an even bigger concern than the action of rogue operators is that SRM could serve as an excuse for nations or industries to avoid or delay taking action to cut their greenhouse gas emissions.
