The hottest summer

[ – 2021.07.20] It’s almost as if the entire East Coast has shifted south. Summers in Portland, Maine, are now almost as hot as summers in Boston were for much of the 20th century. Summers in Boston have come to resemble 20th-century summers in New York. New York, similarly, has come to resemble Philadelphia, which in turn has become hotter than Washington, D.C., or Atlanta were only a few decades ago. Summers in Washington and Atlanta are hotter than summers in Tampa, Fla., used to be.



There is a similar story to tell in the Mountain West, a region that has been enduring a heat wave in recent days. Summers today have come to resemble summers of the past in hotter places:



These are the cascading effects of climate change, and they are getting worse. The data I’m showing you here is based on 10-year averages for July temperatures. I picked this longer time frame to avoid conflating normal year-to-year fluctuations — which have always existed and always will — with the effects of climate change. If anything, these 10-year averages understate how hot summer has become, because climate change continues to exert a small effect every year.

The summer of 2021 appears to be on pace to be the hottest on record. Last month was the hottest June since at least the 1890s (when federal records begin). The temperature reached 116 degrees in Portland, Ore., at one point and 121 in British Columbia, Canada. Climate researchers concluded that those levels of heat would have been “virtually impossible without climate change.”

This month has also been brutally hot in many places. The western U.S. is experiencing its fourth heat wave in less than two months, with temperatures in Montana and Idaho topping 100 degrees this week. On July 9, Death Valley, Calif., reached 130 degrees, matching the hottest temperature recorded on Earth

Numbers aside, the extreme heat is creating situations that are a mix of unnatural and horrific. Dozens of wildfires are burning across the West. Larger wildfires, like the Bootleg fire in southern Oregon, can sometimes create their own weather systems, spawning lightning from towers of smoke or generating a fire whirl, a vortex of air and flame that looks like a fiery tornado.

“Normally the weather predicts what the fire will do,” Marcus Kauffman of Oregon’s forestry department said. “In this case, the fire is predicting what the weather will do.”

Day to day, the summer heat in much of the U.S. is unpleasant. Boston is not supposed to feel like New York, and Philadelphia isn’t supposed to feel like Atlanta.

But the heat is not merely unpleasant. It can be downright dangerous, and the future is looking increasingly dangerous, too.

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