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In Aspen, Wood didn't pull any punches. "He was being outrageous," Caldeira remembers with amusement. "He said something like, 'If we want to solve the global warming problem, we could just have a nuclear war.'" Even the title of his presentation was provocative: "Geoengineering and Nuclear Fission as Responses to Global Warming." By spending only about $1 billion per year, Wood argued, we could put enough particles in the stratosphere to reduce sunlight by about 1 percent — and that's all we'd need to start reversing global warming.
Wood must have known his talk was going to be controversial. Geoengineering had a long history but a checkered reputation. In a 1965 environmental report that discussed climate change (yes, back then), President Johnson's Science Advisory Committee offered a single solution to the problem, and it was a fix that we would now call geoengineering: Spread reflective particles over the oceans.
But as the environmental movement gained momentum, it became decidedly uncool to propose high tech interventions. Geoengineering also suffered by association with several undistinguished military ventures into weather modification. In 1971, news broke that the Pentagon had attempted to alter the weather in Vietnam for military purposes by seeding clouds with silver iodide crystals. The episode prompted an international outcry and, later, a United Nations convention against weather interference for hostile purposes.
Wood's talk didn't generate much enthusiasm among the scientists in Aspen that day. "I thought it would never work," Caldeira says. In fact, he teamed up with another Livermore colleague, Bala Govindasamy, to prove Wood wrong by conducting a thorough climate simulation, the first of its kind. "The intent was to put an end to all the geoengineering talk," Caldeira says. Because changes in the intensity of sunlight affect the climate quite differently than do changes in greenhouse gas concentrations — sunlight varies by season and by the diurnal cycle and falls most strongly over the tropics and equator, whereas carbon dioxide traps heat both day and night across the globe — he had a hunch that the two might not really offset one another very well, especially on a regional or seasonal basis.
When the results came back, Caldeira had disproved his own hypothesis. Geoengineering really did seem to operate more or less like a planetwide thermostat. As the resulting paper noted, Wood's proposal might have any number of adverse environmental and ecological consequences, but it also might offer real benefits. "Melting of Greenland and Antarctic ice caps and the consequent sea level rise," Caldeira and Govindasamy wrote in the spring 2000 issue of Geophysical Research Letters, "is less likely to occur in a geoengineered world."
The paper helped propel Wood's idea into the scientific mainstream and turned Caldeira and Wood into unlikely new allies. Since then, increasingly bad climate news has only heightened interest in the proposal. The summer of 2007 saw a new low in the extent of Arctic sea ice, while data from the Greenland ice sheet is similarly ominous; if it were to melt entirely, sea levels would rise 20 feet, submerging coastal cities like New York and Shanghai. Meanwhile, a new climate-modeling study by Caldeira and another colleague found that in order to stabilize the climate now, we'd have to go to zero emissions almost immediately — something nobody thinks is even remotely possible. All of which is forcing scientists to consider geoengineering more seriously as a way to fight climate change.
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The stratospheric sulfate experiment has already had its proof of concept — courtesy of planet Earth. On June 15, 1991, Mount Pinatubo, which for months had been rumbling, belching, and terrorizing the main Philippine island of Luzon, finally blew its top in an explosion so powerful that it carried 500 feet of the mountain's peak along with it. It was the second-largest volcanic eruption of the 20th century, 10 times the size of the Mount Saint Helens explosion in 1980 and the first of its scale to occur with modern scientific technologies in place — especially satellites — to measure the global environmental and climatic effect.
Pinatubo's eruption didn't just unleash huge mud slides and lava flows; it also fired an ash stream 22 miles into the air, injecting 20 million tons of sulfur dioxide into the stratosphere. Over the following months, a massive haze gradually dispersed across the globe. Meanwhile, the sulfur dioxide component underwent chemical reactions to form a particulate known as sulfate aerosol (in essence, droplets of water and sulfuric acid), which absorbs sunlight and reflects some of it back into space.
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. Hell, we've been modifying the environment ever since we thought about digging a ditch in order to bring water to our crops, homes and animals.
