How to Fix a Climate Emergency

The idea of engineering climate isn't new. In 1965 a report fell on President Lyndon Johnson's desk exploring ways to manipulate climate to compensate for a rise in temperatures. (Oddly enough, the report never mentioned cutting emissions.) The idea made the rounds in scientific circles over the next decades, but by the 1990s it had disappeared from discussion, mainly because policymakers were trying to build a consensus for emissions cuts. "It became so un-PC we couldn't talk about it," David Keith, a physicist at the University of Calgary, told a TED conference in 2007. "It just sank below the surface; we weren't allowed to speak about it."

In 2006 Crutzen, a chemist, broke the ice with a paper in the journal Climate Change. He repeated an idea that originated with Russian physicist Mikhail Budyko, who proposed in 1974 using planes to release sulfur dioxide, or SO2, into the atmosphere, where it would react with water and other molecules to form sulfate particles—the same stuff as volcanic ash. (Crutzen preferred using weather balloons to carry the gas aloft.) Crutzen pointed out that the amount of SO2 you'd need to lower temperatures significantly is surprisingly small—nowhere near the 20 million tons that Pinatubo released, much of which was wasted near the ground where it had no effect on temperatures. By Crutzen's reckoning, it would take about 1.5 million tons to counteract the effects of a doubling of CO2 concentrations from preindustrial levels to 550 parts per million (today's level is 385ppm, but it will certainly rise by the time any geo-engineering scheme goes into effect). Others have put the figure as high as 5 million tons—still nothing that couldn't be handled by a fleet of airplanes for a few billion dollars. The low price is rather astonishing. Britain's authoritative 2006 report on the cost of cutting emissions enough to stabilize temperatures put the price tag at about 1 percent of the world's annual GDP; other estimates run as high as 4 percent. The options for cooling the planet by deflecting solar rays are far cheaper: for one thousandth of 1 percent of GDP, "you could bring on an ice age," says Keith.

Geo-engineering, say critics, would create many nasty side effects. One of the drawbacks to SO2 is that it destroys the ozone layer, exposing people in the Southern Hemisphere to deadly ultraviolet radiation. There's some disagreement over how severe this destruction would be. Mount Pinatubo increased the ozone hole over the South Pole only slightly, but some studies say a large release of SO2 could increase the southern hole and perhaps even cause one to appear in the north as well. One way around the problem is to go slowly—release SO2 a bit at a time, study how the climate responds and try a bit more. If there was big ozone damage, the experiment could be halted and the SO2 would quickly dissipate. This should provide some comfort to people frightened by the idea of engineers permanently tampering with the atmosphere.

Keith is working on designing particles that are more efficient at cooling than sulfates, but without the side effects. Because sulfates tend to settle on the ground after a few months, they'd need to be replenished regularly. Keith's engineered particle would absorb the sun's energy unevenly, causing one side to heat more quickly than the other and to drift upward. Such a particle might be released on the ground and rise up on its own accord. It might be built in such a way that it rises higher than the ozone layer—to the mesosphere, 100 kilometers up—where it would reflect light but leave the ozone intact. For safety reasons, these particles could also have preordained lifetimes. "It's something we're developing," he says. "It may not work. But it's almost certain that if engineers put their minds to this, something could be made to work better than sulfates."

The most devastating side effect could be political. Success in lowering temperatures—or even the knowledge that scientists had the means to do so—might decrease the political will to make costly emissions cuts. Not even the most zealous advocate of geo-engineering argues for using it in lieu of cutting and capturing carbon. Using geo-engineering to keep temperatures artificially low while carbon levels continued to rise would be doubling down the risk of rapid warming should the air-cooling project suddenly stop, or need to be halted, for any reason.

The debate over whether to re-create the Pinatubo effect could eventually turn out to be moot. The technology is potentially so cheap that virtually any nation, or at least a middle-rate power, could undertake a climate-cooling project on its own. And as the grand river-diversion projects of the former Soviet Union and China have shown, certain kinds of regimes are far more confident of their ability to reshape the environment. It's entirely possible that someone is going to use the technology eventually, especially in countries where droughts and other climate-related weather become a political issue. "If one country can do it, another can," says Scott Barrett, an economist at Johns Hopkins University. "Along with climate change, there'll be an increase in political tensions."

The notion of engineering the climate may be frightening, but it may also be unavoidable, which is why policymakers would do well to start thinking about it now. If global warming does accelerate in coming years, any scheme to stop it may start to look safer than the alternative.

With Michael Levitin in Berlin and Sangwon Yoon in New York

© 2009