and all from one location. But geoengineers could choose exactly where to send sulfates into the stratosphere, as well as when and how fast.
Artificial Trees: Various chemical reactions can be used to capture carbon dioxide from the atmosphere for permanent storage. Pros: In the long run, this could reduce atmospheric concentrations of carbon dioxide. There is no obvious limit to how much of the greenhouse gas could be stored. Cons: It could be very expensive and energy intensive, and it would take a long time to reduce temperatures.
“So far we’re thinking about a very simplistic thing,” Schrag says. “We’re talking about injecting stuff in the stratosphere in a uniform way.” The effects that have been predicted so far, however, aren’t evenly distributed. Changes in evaporation, for example, could be devastating if they caused droughts on land, but if less rain falls over the ocean, it’s not such a big deal. By taking advantage of stratospheric circulation patterns and seasonal variations in weather, it might be possible to limit the most damaging consequences. “You can pulse injections,” he says. “You could build smart systems that might cancel out some of those negative effects.”
Rather than intentionally polluting the stratosphere, a different and potentially less risky approach to geoengineering is to pull carbon dioxide out of the air. But the necessary technology would be challenging to develop and put in place on large scale.
In his 10th-floor lab in the Manhattan neighborhood of Morningside Heights, Klaus Lackner, a professor of geophysics in the Department of Earth and Environmental Engineering at Columbia University, is experimenting with a material that chemically binds to carbon dioxide in the air and then, when doused in water, releases the gas in a concentrated form that can easily be captured. The work is at an early stage. Lackner’s carbon-capture devices look like misshapen test-tube brushes; they have to be hand dipped in water, and it’s hard to quickly seal them into the improvised chamber used to measure the carbon dioxide they release. But he envisions automated systems–millions of them, each the size of a small cabin–scattered over the countryside near geologic reservoirs that could store the gases they capture. A system based on this material, he calculates, could remove carbon dioxide from the air a thousand times as fast as trees do now. Others at Columbia are working on ways to exploit the fact that peridotite rock reacts with carbon dioxide to form magnesium carbonate and other minerals, removing the greenhouse gas from the atmosphere. The researchers hope to speed up these natural reactions.
It’s far from clear that these ideas for capturing carbon will be practical. Some may even require so much energy that they create a net increase in carbon dioxide. “But even if it takes us a hundred years to learn how to do it,” Pierrehumbert says, “it’s still useful, because CO2 naturally takes a thousand years to get out of the atmosphere.”
The Seeds of War
Several existing geoengineeringschemes, though, could be attempted relatively cheaply and easily. And even if no one knows whether they would be safe or effective, that doesn’t mean they won’t be tried.
David Victor, the director of the Laboratory on International Law and Regulation at the University of California, San Diego, sees two scenarios in which it might happen. First, “the desperate Hail Mary pass”: “A country quite vulnerable to changing climate is desperate to alter outcomes and sees that efforts to cut emissions are not bearing fruit. Crude geoengineering schemes could be very inexpensive, and thus this option might even be available to a Trinidad or Bangladesh–the former rich in gas exports and quite vulnerable, and the latter poor but large enough that it might do something seen as essential for survival.” And second, “the Soviet-style arrogant engineering scenario”: “A country run by engineers and not overly exposed to public opinion or to dissenting voices undertakes geoengineering as a national mission–much like massive building of poorly designed nuclear reactors, river diversion projects, resettlement of populations, and other national missions that are hard to pursue when the public is informed, responsive, and in power.” In either case, a single country acting alone could influence the climate of the entire world.
How would the world react? In extreme cases, Victor says, it could lead to war. Some countries