Energy & Sustainability Geoengineering: How to Cool Earth--At a Price Global warming has become such an overriding emergency that some climate experts are willing to consider schemes for partly shielding the planet from the sun's rays. But no such scheme is a magic bullet By Robert Kunzig THIS IS A PREVIEW. Buy this digital issue or subscribe to access the full article. Already a subscriber or purchased this issue? Sign In Kevin Hand When David W. Keith, a physicist and energy expert at the University of Calgary in Alberta, gives lectures these days on geoengineering, he likes to point out how old the idea is. People have been talking about deliberately altering climate to counter global warming, he says, for as long as they have been worrying about global warming itself. As early as 1965, when Al Gore was a freshman in college, a panel of distinguished environmental scientists warned President Lyndon B. Johnson that carbon dioxide (CO2) emissions from fossil fuels might cause “marked changes in climate” that “could be deleterious.” Yet the scientists did not so much as mention the possibility of reducing emissions. Instead they considered one idea: “spreading very small reflective particles” over about five million square miles of ocean, so as to bounce about 1 percent more sunlight back to space—“a wacky geoengineering solution,” Keith says, “that doesn’t even work.” In the decades since, geoengineering ideas never died, but they did get pushed to the fringe—they were widely perceived by scientists and environmentalists alike as silly and even immoral attempts to avoid addressing the root of the problem of global warming. Three recent developments have brought them back into the mainstream. THIS IS A PREVIEW. Buy this digital issue or subscribe to access the full article. Already a subscriber or purchased this issue? Sign In Buy Digital Issue $7.99 Add To Cart Print + DigitalAll Access $99.99 Subscribe ADVERTISEMENT Scientific American is a trademark of Scientific American, Inc., used with permission © 2015 Scientific American, a Division of Nature America, Inc. All Rights Reserved.