There is no precedent in contemporary weather records for the kinds of droughts the country’s West will face, if greenhouse gas emissions stay on course, a NASA study said. No precedent even in the past 1,000 years. The feared droughts would cover most of the western half of the United States -- the Central Plains and the Southwest. Those regions have suffered severe drought in recent years. But it doesn’t compare in the slightest to the ’megadroughts’ likely to hit them before the century is over due to global warming.