The Pinatubo option could have some very unpleasant side effects, too. An Indian space scientist suggested that deploying the scheme might disrupt various monsoon cycles that provide water to hundreds of millions of people across the world. Granger's graduate student got up afterward and warned the group that computer simulations suggest the technique might lead to a drop in global rainfall. (The aerosols would block solar energy, which drives precipitation systems. She did note that higher temperatures in a world without geoengineering might also yield drier areas.)
Whatever its specific effects, it's easy to see how geoengineering would create confusion and sow international conflict. "If a country like the United States were to do this on their own and China [happened] to go into a decadelong drought, [the Chinese would] want to know what was the cause," explained Ken Caldeira, a geochemist from the Carnegie Institution. "Climate science is not at the point of attributing the cause of weather events." Not every expert at the meeting thought that the unilateral scenario was realistic, but no one downplayed the emerging strategic risk that geoengineering represents. Some mused that rich individuals or corporations—"climate pirates" perhaps?—might even issue their own "Pinatubo ultimatum."
None of the participants were eager to geo-engineer; they'd much rather see humanity stem the problem by ending its greenhouse-gas binge. But they wonder whether it may one day become a necessity. At any rate, it's better to explore it now, they say, so we're as prepared as possible. Everyone at the meeting thought field tests were inevitable fairly soon.
It's not clear how nations would go about regulating such a technology. "There aren't very good analogies," University of Maryland arms-control expert John Steinbruner told me. Treaties that might apply—the Weather Modification Convention, the Outer Space Treaty, the ol' Law of the Sea—wouldn't really cover geoengineering experiments or deployments, he said. Participants wondered whether the U.N. Security Council or a new international treaty might eventually regulate geoengineering, but to cover experiments on the shorter term, scientific societies, national science academies, or the Intergovernmental Panel on Climate Change were each proposed as possible venues for some sort of geoengineering accord.
Or is it too early to be discussing the Pinatubo option at all? Just under the surface of the Lisbon workshop lurked the ever-present worry among scientists that exploring geoengineering could dissuade the public from aggressive and expensive emissions-cutting measures—the risk of moral hazard. In a way, one might hope that the geoengineering alternative weren't available at all, said University of Calgary physicist David Keith. He asked us to imagine one could open a box ("call it Pandora's box") to find out for certain whether it would work. "Which do you wish for?" If it does work, it's going to be a colossal mess, he said. "But on the other hand, if it really serves to be a method of reducing the climate risk, and the climate risk is the essential thing. …" Later, he e-mailed me: "We should wish it works," he wrote.