Washington Post: Could climate change be staved off by making the United States look like the set of “Mamma Mia!”? That was suggested in a recent talk by Energy Secretary Steven Chu — although, because he was speaking to Nobel laureates, he did not mention the ABBA musical set in the Greek Islands. He said that global warming could be slowed by a low-tech idea that has nothing to do with coal plants or solar panels: white roofs. Making roofs white “changes the reflectivity . . . of the Earth, …