Nature has a method of cooling the planet very rapidly: volcanos.

Volcanic eruptions have, historically, caused sudden (but temporary) changes to global climate. The sulfur particles they shoot into the atmosphere reflect sunlight back at the sun, reducing temperatures back on the ground. The 1991 eruption of Mount Pinatubo in the Philippines caused a reduction in Northern Hemisphere temperatures of about 0.6 degrees Celsius; for comparison, man-made global warming has heated the planet by about 1 degree Celsius so far, and a United Nations report this fall urged policymakers to limit total warming to 1.5 degrees.

The scale of volcanic cooling has given some climate scientists an idea: Could we forestall the worst consequences of global warming by spraying sulfur particles into the atmosphere — basically, by using technology to emulate a massive volcano?

In the latest episode of Future Perfect, we explain solar geoengineering, as experts call this idea. If it sounds scary to you, it should! It has for years been a somewhat taboo subject among scientists. Spraying chemicals into the atmosphere sounded outlandish and reckless, and, worst of all, like a distraction from the key task of reducing carbon emissions. And to be clear, we absolutely need to reduce climate emissions, no matter what.

But as the US withdraws from the Paris climate deal, and Brazil’s new far-right president threatens to do the same, scientists and advocates are increasingly recognizing that we need to research unconventional ways to fight climate change. And they see solar geoengineering as a last resort to prevent utter catastrophe. We might need to know how to do it, even if we just keep it behind a glass door marked “Break in Case of Emergency.”

And we need to be talking about it in case one country decides to go it alone and geoengineer without international cooperation. Given that any government could conceivably engage in this project for only about $10 billion a year (a pittance for a number of large or rich countries affected by climate change, like India, China, or the whole developed world), it will become very tempting for a country looking to avoid displacing citizens due to sea level rise, or trying to prevent catastrophic weather events, to spray aerosols into the atmosphere unilaterally.

“I don’t know whether that’ll happen in five or 10 or 50 years,” Gernot Wagner, a Harvard economist and expert on geoengineering, told us, “but somebody somewhere will attempt to pull the trigger on this. And even if you think it’s nuts that anyone would consider this to be part of a semi-rational climate policy portfolio … wouldn’t it be good to know more about this technology, about the impact, about the efficacy, about the risks, if and when somebody is compelled to pull the trigger?”

Read more:

Brad Plumer explains the basics of geoengineering at Vox

Umair Irfan walks through a recent study on the limits of geoengineering; thanks to Irfan for his help on this episode

Irfan and the Vox visuals team’s interactive on US weather in 2050

The Stratospheric Controlled Perturbation Experiment, led by Harvard professor Frank Keutsch, seeks to learn more about the likely effects of solar geoengineering without actually doing it

Gernot Wagner and his colleague Martin Weitzman make the cautious case for taking solar geoengineering seriously at the Wall Street Journal

More of Vox’s effective altruism coverage

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