Call it spring hellfire, the Heat Miser’s meddling or the harbinger of summer — a historic heat wave is descending on Arizona, bringing three-digit temperatures to Phoenix. But this week’s record-breaking heat is not the stuff of myth or legend, experts warn: It’s on trend for a warming planet. The heat is the result of a high-pressure system spinning across the West, causing “an expansive dome of unusually hot temperatures,” NOAA’s National Weather Service Weather Prediction Center said in a Facebook post on March 16.