Reducing the amount of sunlight reaching the Earth could take the edge off global warming and limit the damage caused by climate change, according to Britain’s leading scientific body.
But the Royal Society has warned that strategies aimed at bringing about these changes are not without risk.
The society, which sparked the scientific revolution in the 17th century, said in a new report that bold new technology for reflecting sunlight back into space could “buy time” for cuts in fossil fuel emissions to take effect.
It said two strategies – pumping reflective particles high in the atmosphere and spraying salt into clouds over the sea to make them whiter – are likely to be effective, as well as technically feasible.
But the report’s authors warn a rogue nation going alone, and attempting to dim sunlight in one region, could cause extreme droughts and other weather disturbances elsewhere in the world.
Professor Keith Shine, chair of the report’s working group, said there could nevertheless be a time when world leaders agree that solar radiation modification (SRM) is the least worst option.
“This is not a question of whether SRM is safe, as it is clearly not without risks,” he said.
“However, there may come a point where those risks are seen to be less severe than the risks of insufficiently mitigated climate change.”
The report said global efforts to reduce greenhouse gas emissions look increasingly unlikely to stop global temperatures rising above 1.5C, considered by many scientists to be a “safe” limit.
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A new round of UN climate talks will start later this week in Brazil, but under current policies, temperatures are likely to be at least 3C warmer than pre-industrial times by 2100.
The working group ranked stratospheric aerosol injection as the most promising option for dimming the amount of sunlight reaching the Earth’s surface.
Planes would fly at high altitude, releasing sulphur dioxide gas, which would form particles that reflect a small amount of sunlight.
There is real-world evidence that this could work. The 1991 eruption of Mount Pinatubo, a volcano in the Philippines, pumped 15 million tonnes of sulphur dioxide into the stratosphere, reducing the temperature by 0.5C for one to two years.
Computer models suggest that releasing eight to 16 million tonnes of the gas from planes each year across both the northern and southern hemispheres could reduce the global temperature by 1C.
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The likely cost would be “in the low 10s of billions of dollars a year”, said Prof Shine.
That’s far less than the global cost of more extreme weather, wildfires, and other climate impacts.
Hurricane Melissa, which was made more intense by global warming, cost up to $52bn (£39.9bn) in damage and economic losses across the western Caribbean, according to AccuWeather.
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The Royal Society’s report warns that SRM would not tackle the root cause of climate change, and is not an alternative to reducing emissions.
But it could reduce temperatures while carbon dioxide levels in the atmosphere peak and begin to fall. It could mean SRM would need to be deployed for 100 years or more.
