Solar geoengineering: Climate-solution or Pandora’s box?
The EU’s executive arm has called for international talks on a potential framework to address the dangers and governance issues of SRM.

It’s simple physics — if we spray aerosols into the stratosphere for long enough, eventually they will start to reflect the sun rays and reverse catastrophic global warming. That’s what the proponents of solar geoengineering say. But its many opponents say it’s a dangerous gamble on a planetary level and that the potential consequences are so complicated it should not even be considered as an option. After spending years as a relatively obscure idea, solar geoengineering is now gaining increasing prominence among lawmakers, academics and even UN climate body IPCC, with the alluring possibility of taking the planet back to pre-industrial temperatures even as humanity dithers on ramping down carbon emissions.
US President Joe Biden’s administration has argued the case for a coordinated research program into solar radiation management (SRM) — a term describing geoengineering efforts to reflect the sun. Still, the United States has stressed it has no plans to launch such a program.
The EU’s executive arm has called for international talks on a potential framework to address the dangers and governance issues of SRM.
How does it work?The most prominent approach involves spraying tiny droplets of sulfur dioxide into the stratosphere — the atmospheric layer between 10 and 50 km above the earth’s surface. There they can survive for about one year, reflecting sunlight and cooling the planet. The principle was demonstrated by the 1991 volcanic eruption of Pinatubo in the Philippines. Its blast was so powerful that it injected about 15 million tons of sulfur dioxide right into the stratosphere. The eruption cooled the planet by more than half a degree Celsius over the following two years.
Modeling shows that reflecting 1% of the sunlight reaching earth would be enough to cool the planet to pre-industrial levels, according to Douglas MacMartin, a senior research fellow at Cornell University in the US. Research shows also that replicating such an injection of sulfur dioxide into the stratosphere isn’t practically difficult. MacMartin added the cost of deployment would be relatively low, with one paper estimating $18 billion annually. That’s much less than the damage already caused by climate-fuelled extreme weather.
“Relative to the damages from climate change, it’s basically free,” MacMartin said. That’s not to say it would be simple. It would likely involve hundreds of aircraft stationed around the world. They would fly thousands of flights a year over the next century, constantly spraying aerosols in the atmosphere. Deploying such technology would affect the entire planet too. It may sound reckless, but proponents point out that we already pump about 10 times more aerosols into the lower atmosphere, as a result of regular pollution. This too has a cooling effect but is associated with other health and ecological hazards.
What are the downsides?Not all the possible effects are fully understood, but scientists already know that the aerosols would produce acid rain, and would deteriorate the ozone layer, which according to the UN is helping to prevent more warming. It would also affect precipitation patterns, potentially exacerbating catastrophic weather systems — already made worse by climate change — in some areas. Other, more catastrophic effects may come to light with further research. And while reflecting the sun with aerosols would cool the planet, it cannot reverse other effects of climate change, such as ocean acidification.