With three-quarters of the US west gripped by a seemingly ceaseless drought, several states are increasingly embracing a drastic intervention – the modification of the weather to spur more rainfall. … Cloud seeding experiments have taken place since the 1940s but until recently there was little certainty the method had any positive impact. But research last year managed to pinpoint snowfall that “unambiguously” came from cloud seeding … Others are now looking to join in, including the “four corners” states – Utah, Arizona, Colorado and New Mexico – that have been ravaged by the most extreme version of the latest drought.