We can cool our warming planet by blocking sunlight in the atmosphere. Is this hubris or a way of mitigating the damage we've already done?

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The world is decarbonizing as fast as possible, but it’s not fast enough. Climate change is already happening, bringing worse droughts, stronger storms, rising seas, and all the other crises that scientists warned us about for years. Even if, by some miracle, the world’s coal and gas plants all transmuted into solar panels and wind turbines overnight, it wouldn’t undo the harm we’ve already done.

Direct air capture is the real cure for climate change. We have the technology to pull carbon dioxide out of the atmosphere and lock it away in stable rock formations. If we did this on a planetary scale, we could undo two hundred years of heedless burning. We could reset Earth’s climate to its pre-industrial state, and keep it in a stable band thereafter.

The problem is the price tag. Unless carbon-capture technology gets dramatically better, doing this would cost trillions of dollars and could take hundreds of years. In the meantime, humanity has no choice but to suffer the ravages of climate change.

Or do we?

The year without a summer

In April 1815, a volcano in Indonesia erupted catastrophically. The explosion of Mount Tambora was colossal, most likely the largest in recorded history. Lava and pyroclastic flows wiped out all life on the island of Sumbawa, and ash rained down in an 800-mile radius. The geologist Charles Lyell wrote about it:

In April, 1815, one of the most frightful eruptions recorded in history occurred in the province of Tomboro, in the island of Sumbawa… The sound of the explosions was heard in Sumatra, at the distance of 970 geographical miles in a direct line; and at Ternate, in an opposite direction, at the distance of 720 miles. Out of a population of 12,000, in the province of Tomboro, only twenty-six individuals survived.

…The darkness occasioned in the daytime by the ashes in Java was so profound, that nothing equal to it was ever witnessed in the darkest night.

…The town called Tomboro, on the west side of Sumbawa, was overflowed by the sea, which encroached upon the shore so that the water remained permanently eighteen feet deep in places where there was land before.

Principles of Geology, 1853, chapter XXVII

When a volcano erupts this violently, it flings ash, dust and particulates into the upper atmosphere, where air currents disperse them around the planet. The heavier bits soon rain out, but lighter dust particles form a haze that can linger for months. In addition, volcanoes spew out sulfur compounds which react with water to form sulfate aerosols: microscopic, floating droplets of sulfuric acid.

Together, ash and sulfate aerosols raise Earth’s albedo (literally, its “whiteness”). Like atmospheric insulation, they reflect sunlight back into space, cooling the planet down.

That’s what happened in the months after the Mt. Tambora eruption. Global temperatures fell, and the sun was reddened and dimmed by a haze of atmospheric dust. In 1816, across New England and Canada, there was heavy snowfall in June and frost as late as August. Crops withered in the freezing temperatures, and famine followed swiftly after. In Rhode Island and New Hampshire, governors called on their people to pray and beg God for forgiveness.

In Europe, too, the summer of 1816 was cold and wet, causing floods and crop failures. Food prices spiked, thousands of poor people died of hunger, and there were riots, looting and disease outbreaks. Newspapers called it “the year without a summer“.

(An interesting side note: That summer, a group of authors and poets including the famed Lord Byron gathered at Lake Geneva in Switzerland. Because the weather was too wet and gloomy for outdoor recreation, Byron proposed telling ghost stories to pass the time. One member of the company who took him up on that offer was a young writer named Mary Shelley.)

Make your own volcanic winter

When the world was pre-industrial and the climate was more temperate, this temporary cooling produced devastating famine. But now the planet is getting too hot. Could a little cooldown be just what the doctor ordered?

We have the technology to do artificially what Mount Tambora did naturally. We could fly airplanes through the stratosphere, spraying a mist of sulfate aerosols as they go—like salt-spreading trucks on an icy road. If we did this in a precise quantity, could we counteract the effects of global warming?

This idea goes under the heading of solar geoengineering. We’ve known for a long time that this is feasible, but as climate change becomes inevitable, more and more people are giving it serious consideration. As part of its 2022 spending plan, the Biden White House commissioned a five-year study into the risks and benefits of this and other strategies for cooling the planet.

The most tempting thing about solar geoengineering is that it’s shockingly cheap. By some estimates, it would cost just $10 billion per year to cool the Earth by 1 degree Celsius. That’s a vanishingly small sum compared to every other mitigation strategy that’s been proposed. Nothing else gives us this much bang for the buck when it comes to fighting climate change.

Of course, this approach has downsides. Those sulfate aerosols will eventually come back down as acid rain, which is destructive in its own right. It corrodes metal, eats away at stone, kills forests and contributes to ocean acidification that destroys coral reefs. Sulfates also boost the formation of halogen radicals that chew holes in the ozone layer. (Some scientists are studying whether it’s possible to use different chemical compounds that have the same cooling effect without the problems of sulfates.)

But the biggest, most glaring downside of solar geoengineering is that it’s yet another way for us to kick the can down the road. If it gives us a band-aid we can slap over climate change, fossil fuel corporations and other big polluters would argue that there’s no need for them to change their ways. And once we started doing it, if we ever stopped, global temperatures would rebound within a few years, causing even more drastic and destructive climate swings.

However, we may not have the luxury of debating this forever. Solar geoengineering is so cheap that many nation-states could afford to do it on their own. There’s a chance that as the harms of climate change stack up, the worst-affected countries will decide to go ahead without consulting the rest of humanity.

This is a plot element in Kim Stanley Robinson’s cli-fi novel The Ministry for the Future. In the book, after a deadly wet-bulb heat wave kills millions of people in India, the Indian government starts unilaterally spraying sulfates into the atmosphere to cool the planet.

Should we do it?

While solar geoengineering has serious downsides, we have to ask: compared to what? If we do nothing, we’re barreling toward a future of more and worse droughts, wildfires, floods, killer heat waves, mass migrations, possibly even wars. How do the costs of this idea measure up against the cost of inaction?

Personally, I’m no longer persuaded by the moral-hazard argument that it gives license to polluters. That argument would have had more force ten or twenty years ago, but the green transition is already in progress:

Since 2010, the cost of solar power and lithium-battery technology has fallen by more than 85 percent, the cost of wind power by more than 55 percent. The International Energy Agency recently predicted that solar power would become “the cheapest source of electricity in history,” and a report by Carbon Tracker found that 90 percent of the global population lives in places where new renewable power would be cheaper than new dirty power.

…Globally, there are enough solar-panel factories being built to produce the necessary energy to limit warming to below two degrees, and in the United States, planned solar farms now exceed today’s total worldwide operating capacity.

Beyond Catastrophe: A New Climate Reality Is Coming Into View.” David Wallace-Wells, The New York Times, 26 October 2022.

Renewables are so cost-effective that they’re all but certain to displace fossil fuels soon. These economic realities won’t be affected by what we do or don’t do to the sky.

Given these facts, I’m cautiously willing to believe that solar geoengineering could be part—not all, but a part—of humanity’s climate-adaptation portfolio. It’s something we can do to slow down warming while we implement more permanent solutions. We’re already so close to the tipping points, both good and bad. If we can buy ourselves only a decade or so, that may be all we need to claw our way onto the better path.

DAYLIGHT ATHEISM—Adam Lee is an atheist author and speaker from New York City. His previously published books include "Daylight Atheism," "Meta: On God, the Big Questions, and the Just City," and most...

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