A new study finds that much of the western United States is baking in what scientists call an emerging megadrought.
Thursday's study in the journal Science blames almost half the problem on man-made global warming, which scientists say is only getting worse. Multi-decade deep droughts happen every couple of hundred years. But the current one is one of the most severe since the year 800. Some scientists say this drought, which started in 2000, may not have lasted long enough yet to qualify as a megadrought.