The sun blotted out from the sky

But purely scientific disagreements about geoengineering are just the tip of the melting iceberg. Questions of usefulness and necessity aside, grand-scale sun-blocking schemes feel dubious in part because they challenge our intuitive sense that large-scale wrongs can be atoned for only with equally large-scale sacrifices. Drastic emissions cutbacks require drastic lifestyle changes, like taking shorter showers and scrapping the Hummer. Such changes feel right because they're a little painful; putting the squeeze on ourselves is suitable penance for the collective sin of spewing tailpipe fumes into the atmosphere for the past 100-plus years.

Geoengineering, by contrast, seems like an undeserved dispensation, a free-lunch promise that technology can whitewash our past transgressions. Let's go on a fossil fuel binge, never mind the CO₂ hangover; scientists will cure it by blotting out the light and fertilizing the oceans! "It's like giving alcohol to a drunk; you've got a knife in your drawer so you can put in a new liver if he ever needs it," said Dale Jamieson, director of environmental studies at New York University, at February's AAAS conference.

Still, even the most skeptical scientists concede that it makes sense to consider geoengineering as a last-ditch option, a kind of nuclear football that can be deployed if warming becomes too dire -- if Manhattan threatens to slip under the waves, say, or if the Fertile Crescent shows signs of turning into a barren wasteland. "We need to do more research to figure out whether geoengineering is possible in an emergency situation," Robock says.

Assuming for a moment the patient might need a new liver someday, who's going to perform the transplant? Existing international laws could complicate the procedure; a 1977 United Nations convention prohibits countries from using environmental modification techniques that could have "widespread, long-lasting or severe effects" on any other nation. That means that if a government-funded geoengineering scheme has the potential to disrupt global weather patterns, countries whose interests stand to be affected could legitimately shut it down. And that's leaving aside the thorny question of how to achieve climate-engineering consensus on a global scale. "Whose hand would be on the thermostat?" Robock says. "What if India wants it cooler and Russia wants it warmer?"

Which states emerge triumphant in squabbles like this may end up being a moot point. The 1977 U.N. convention, like so many drafted during that era, places no specific restrictions on the activities of private citizens. Since geoengineering measures tend to be much more affordable than emissions-reduction ones (dirt and sulfur aren't exactly hot commodities), a future Bill Gates or Richard Branson could theoretically kick off an artificial climate-cooling program with little or no input from the rest of the world. "The cost to spray particles over the Arctic would be a couple hundred million dollars a year; and for the whole planet, it's a few billion a year," Benford says. "That's the thing that terrifies geoengineering's opponents -- that this is at least a thousand times cheaper than anything else." Indeed, the strategy's very accessibility may be what makes it the most perilous. Who's to say some rogue entrepreneur, however well intentioned, won't plunk down part of his multibillion-dollar nest egg to send up a fleet of sulfur-spraying planes, putting the Northern Hemisphere under a perpetual cloud and touching off other climatic consequences yet to be foreseen?

Still, taking the giant -- and, in Benford's view, necessary -- global leap of committing to geoengineering fixes may require private-sector intervention, as no society today seems willing to put so much faith in a single technological solution. "Everybody talks about [geoengineering] as though it's a matter of mass action, but I don't think it is -- I don't think it can be," Benford says. "The reason nothing's being done is that governments are ever slower to act."

But putting our fate in the hands of a flash-in-the-pan environmental dabbler with money to burn is especially risky given that adopting a geoengineering venture would be like putting the planet on methadone. It might save us from hitting climatic rock bottom, but it would also require fastidious commitment to a treatment program with no real end in sight. Whether any entity, commercial or governmental, would be able to carry out the necessary upkeep for millenniums -- independent of regime changes, cultural shifts and shadowy future catastrophes -- is still an open question. "Only one or two organized bodies have been able to carry down their traditions for a thousand years," Benford says. "It's a challenge for our civilization. Future societies are going to have to place their trust in a technological enterprise as they never have before."

But all that's far enough in the future that it still feels reassuringly abstract. For now, geoengineering gurus like Benford are concentrating their efforts on the most immediate task at hand: securing funding to test their grandiose plans in the Arctic and other trial venues. It'll be an audition, a chance for these off-off-Broadway productions to prove that they deserve a place on the biggest stage of all -- and the results of the demo round could help determine what life on this planet will be like for the next thousand years. "Is geoengineering a pipe dream, or something that could actually save the future of mankind?" Michaelson says. "We need to figure out which one is true."

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