evidence: Hansen, who is sixty-eight, has greenish eyes, sparse brown hair, and the distracted manner of a man who’s just lost his wallet. (In fact, he frequently misplaces things, including, on occasion, his car.) Thirty years ago, he created one of the world’s first climate models, nicknamed Model Zero, which he used to predict most of what has happened to the climate since. Sometimes he is referred to as the "father of global warming," and sometimes as the grandfather. Hansen has now concluded, partly on the basis of his latest modelling efforts and partly on the basis of observations made by other scientists, that the threat of global warming is far greater than even he had suspected. Carbon dioxide isn’t just approaching dangerous levels; it is already there. Unless immediate action is taken—including the shutdown of all the world’s coal plants within the next two decades—the planet will be committed to change on a scale society won’t be able to cope with. "This particular problem has become an emergency," Hansen said.