Dr. Steven Chu, Obama’s energy secretary, has a simple solution to combating global warming—whitewashing roofs and making roads the colour of cement. It sounds too easy, but Chu, a physicist and Nobel Prize winner, says the idea could cut as much greenhouse gas as parking every car in the world for 11 years. Pale surfaces reflect about 60 per cent more light than dark ones, meaning one coat of paint could greatly reduce solar radiation in the earth’s atmosphere. This would also keep buildings and cities cooler, reducing energy demands for air conditioning. The idea has already caught on in California, where new laws require all flat-topped commercial buildings to have white tops, and soon only cool colours will be allowed on pitched roofs.