Here’s a novel idea for putting the brakes on global warming: Ask everyone in the world to paint their roofs white. U.S. Energy Secretary Steven Chu raised the idea last week at a conference in London, noting that the proposal, first put forth by researchers at Lawrence Berkeley National Laboratory in California, would reflect enormous amounts of sunlight off the Earth’s surface, causing a cooling effect. Dark-colored surfaces’ absorb heat; white and other light colors reflect it. This “completely benign” geoengineering scheme, Chu says, would be the global-warming equivalent of turning off every car on Earth for a decade. The idea’s supporters say it would also cut energy consumption by cooling buildings and reducing the need for air conditioners.