Global warming has made the severe heat wave that has smothered much of Pakistan and India this spring hotter and much more likely to occur, climate scientists with World Weather Attribution, a collaborative effort among scientists to examine extreme weather events for the influence, or lack thereof, of climate change, said Monday. They said that the chances of such a heat wave increased by at least 30 times since the 19th century, before widespread emissions of planet-warming gases began. The relentless heat, with temperatures soaring beyond 100 degrees Fahrenheit for days, particularly in Northwestern India and Southeastern Pakistan, has killed at least 90 people, led to flooding from glacial melting in the Himalayas, contributed to power shortages and stunted India’s wheat crop, helping to fuel an emerging global food crisis. The study found that a heat wave like this one now has about a 1 in 100 chance of occurring in any given year. Before warming began, the chances would have been at least about 1 in 3,000. And the chances would increase to as much as 1 in 5, the researchers said, if the world reaches 2 degrees Celsius of warming, as it is on track to do unless nations sharply reduce emissions.”