The heat waves moving in recent days across Canada, the U.S., and northern Europe are part of a dangerous new climate pattern
By Chico Harlan and Ben Noll, Washington Post
Because of the sweltering heat, Toronto has kept outdoor swimming pools open until nearly midnight. Brits are decamping to the seaside. The French have lugged fans out of storage to deal with the steamy nights. The Netherlands went so far as to cancel several outdoor music performances and sporting events.
These are the markings of a summer at its deepest and most punishing.
But summer has just begun.
The heat waves moving in recent days across Canada, the northeastern United States, and northern Europe have one thing in common: They are occurring quite early in the season. That timing speaks to a broader trend, connected to human-caused climate change, in which summerlike weather is creeping earlier into June and lingering deeper into September — elongating the period of potentially extreme weather and amplifying heat risks.
“There is definitely an extension of the summer period into the shoulder months,” said Carlo Buontempo, director of Europe’s Copernicus Climate Change Service.
This shift is occurring remarkably quickly.
In a typical year between 1979 and 2000, the average Northern Hemisphere temperature would break the 21 degrees Celsius (69.8 degrees Fahrenheit) threshold — indicative of the hottest period — starting around July 10 and continuing for about five weeks, according to data from the University of Maine’s Climate Change Institute.
But last year, the hottest on record, the Northern Hemisphere’s average temperature held above 21 Celsius from June 13 until Sept. 5.
This year is not quite on the same historic pace — but it is still weeks ahead of the normal summer from a few decades ago. As of last week, the latest for which data was available, the average Northern Hemisphere temperature already stood at 20.91 Celsius (69.6 Fahrenheit).
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