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Science  :  Planet Earth  
Can a Million Tons of Sulfur Dioxide Combat Climate Change?
By Chris Mooney 06.23.08

Ken Caldeira devised simulations to discredit geoengineering. But the surprising results converted him.
Photo: Todd Hido
It was one of the largest publicdemonstrations in US history. On June 12, 1982, an estimated 750,000 protesters thronged Central Park in New York City, chanting "No nukes!" and bearing signs reading "Reagan is a bomb — both should be banned" and "Arms are for embracing." Some demonstrators called for unilateral US disarmament, others for renewing arms control talks with the Soviet Union. It was a diverse coalition that had been pulledtogether by Ken Caldeira, a 25-year-old activist and computer geek. Back then he was paying the rent doing software consulting on Wall Street, but his passion for the environment would eventually lead him to become one of the nation's leading experts on global warming.
Around the same time, at the Lawrence Livermore National Laboratory near San Francisco, Lowell Wood — then 41 and a protégé of thebrilliant and controversial hydrogen bomb inventor Edward Teller — was leading a secretive team of young geniuses called the O Group. They weren't merely working with the nukes that Caldeira and his fellow peaceniks reviled; they were dreaming up new and expanded uses for them. One plan called for channeling the energy of a hydrogen bomb into laser blasts that could theoretically destroy enemyballistic missiles from outer space. It sounded crazy, but Wood and Teller's ideas inspired President Reagan's famous March 23, 1983, "Star Wars" speech introducing the Strategic Defense Initiative, the bane of arms-control advocates everywhere.
What's surprising, then, is that today, 25 years later, Caldeira, the left-wing environmentalist, calls Wood, the Cold Warrior and Star Wars proselytizer,"one of my best friends." Recently, they have collaborated on strategies for a process known as geoengineering: the large-scale, deliberate modification of the planet to counteract the consequences of ever-increasing concentrations of atmospheric greenhouse gas. The global climate crisis has made for strange bedfellows, and Caldeira's passage from devout environmentalist to would-be geoengineerhas led him into a partnership that his younger self would have scorned.
Geoengineering schemes sound like they're pulled straight from pulp sci-fi novels: Fertilize the oceans with iron in order to sequester carbon dioxide; launch fleets of ships to whip up sea spray and enhance the solar reflectivity of marine stratocumulus clouds; use trillions of tiny spacecraft to form a sunshade a millionmiles from Earth in perfect solar orbit. They all may seem impractical, but among a small but growing set of climate scientists, one idea that Wood and Teller started pushing in the late 1990s (before Teller's death in 2003) is gaining acceptance: Inject sulfur dioxide into the stratosphere to reflect a portion of the sun's rays back into space, thus cooling the planet.
Ken Caldeira is aself-described blabbermouth with disheveled curly hair and a habit of modestly turning his voice up at the end of sentences so even his most definitive utterances sound like questions. On a recent morning in his Carnegie Institution office on the Stanford campus, he's dressed casually in a sweater and jeans, eagerly examining results from a new climate model run that was designed to explore possibleconsequences of geoengineering. As Caldeira tinkers with the software, he jokes that his talent with computers basically ensured that he would spend more time in an office than out leading research expeditions. A career in science, he says, "was all a ploy for me to get into the rain forests. But it never really worked."
Caldeira's transit from antinuke activist to climate scientist grew out of his...
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