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Extreme hot spells rising

Temperature records reveal inexorable warming and increasing episodes of extreme heat

It’s not your imagination. Not only are extremely hot temperatures occurring more frequently across the globe, but those heat waves are getting more severe.

Back in the 1950s, temperatures on any given summer day were just as likely to be near average as they were to be unseasonably high or low. Climatologist James Hansen of NASA’s Goddard Institute for Space Studies in New York City likens that scenario to rolling a die with two sides each corresponding to low, average and above-normal temperature.

Since the 1980s, that metaphorical die has increasingly become weighted toward delivering a warm day, Hansen and his coworkers report August 6 in the Proceedings of the National Academy of Sciences. In fact, Hansen says, since 2000 it’s as though on any roll almost 4.5 sides will draw hotter than average summer heat.

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