You may not have heard, says Bill McKibben in The New Yorker, but scientists already know how to reverse global warming. It’s called solar geoengineering, and basically involves spraying particles of some “highly reflective” material – probably sulphur dioxide – into the stratosphere to deflect sunlight. This already happens naturally with big volcanoes: an eruption like that of Mt Pinatubo in the Philippines in 1991 can “measurably cool the world for a year or two”. And it’s cheap – climate boffins reckon it would cost only a few billion dollars a year. The thing is, everyone who studies this technique “seems to agree that it’s a terrible thing”. Because the question isn’t whether solar geoengineering can work. It’s: “What else would it do?”
On an environmental level, it could “turn the sky hazy or milky”, damage the ozone layer and diminish the quality of light that plants use for photosynthesis. After the largest volcano eruption ever recorded, in 1815 in what is now Indonesia, it led to a “year without a summer” across much of the northern hemisphere, resulting in plummeting grain yields. Perhaps the biggest problem, though, is that solar geoengineering would affect different places in different ways – and that could easily lead to conflict. “Imagine if India started pumping sulphur into the atmosphere only to see a huge drought hit Pakistan.” Yet despite all these issues, scientists are increasingly convinced we’ll eventually have to resort to something like it. Because if we can’t reduce carbon emissions enough to stop the planet warming, what choice will we have? Keep watching the world burn, or roll the dice?