This whole climate-change debacle could be significantly slowed down if the world’s 100 largest cities thing installed white roofs and more-reflective pavement, says a new study to be published in the journal Climatic Change. It may sound like greenwhitewashing, but physicist Hashem Akbari crunches the numbers: By bouncing heat away from the Earth, a 1,000-square-foot white roof offsets 10 metric tons of greenhouse gases. Roofs account for 25 percent of the surface of most cities, and pavement makes up some 35 percent. Thus, going White-House-style could offset 44 billion metric tons of greenhouse gases — more than is emitted by Earthlings each year. “I call it win-win-win,” says Akbari. “First, a cooler environment not only saves energy but improves comfort. Second, cooling a city by a few degrees dramatically reduces smog. And the third win is offsetting global warming.” We’d help the cause by wearing white, but sorry, it’s after Labor Day.