This heatwave across much of the northern hemisphere could continue for weeks, and possibly even months. And accelerated warming in the Arctic compared to the rest of the planet could be a key contributor.
The heatwaves have killed dozens in Japan and Korea, triggered wildfires in California and Sweden, and led to prolonged dry weather in the UK and across northern Europe, raising temperatures beyond 30°C in Scandinavian sectors of the Arctic Circle. In Greece, the deadliest wildfires in more than a decade have claimed at least 74 lives.
“It could persist for weeks, potentially for months,” a spokesperson for the UK Meteorological Office told New Scientist.
The outlook was echoed by the German Weather Service, DWD, which warned this week of “a continuation of the drought situation and above-normal temperatures for at least the next two weeks for Northern Europe, from Ireland to the Baltic States and southern Scandinavia”.
Last week, temperatures exceeded 30°C in the Scandinavian region of the Arctic Circle, with Norway recording a record high temperature of 33.5°C in Bardufoss, a town just south of Tromsø. More than 50 forest fires raged through Sweden in mid-July.
Heatwaves in Japan and South Korea have claimed at least 40 and 10 lives respectively, with high temperatures and dry conditions triggering wildfires in California. In Algeria’s Sahara Desert, a temperature of 51.°C was recorded on 5 July, a record for Africa, and Canada has already seen 18 days exceeding 30°C, compared with nine all last summer.
Stalled jet stream
One reason is that the jet stream—a fast-flowing river of air snaking continually round the northern hemisphere at altitudes of around 6 kilometres—has stalled over Europe since May, and could continue to do so, trapping regions of high pressure that are cloudless, windless and extremely hot.
“It’s been a key player in the astounding heatwaves across the UK and Scandinavia this summer,” says Jennifer Francis of Rutgers University in New Jersey.
She says evidence is mounting that accelerated warming of the Arctic is a major reason why the jet stream keeps getting stalled. The stream is driven by collisions between cold air descending southward from the Arctic and warm air pushing northward from the equator.
Find out more at New Scientist Live: The greening of the Arctic
The greater the temperature difference between the colliding air streams, the more powerful the jet stream. But the temperature gap—and therefore the power of the jet stream—is being weakened because the Arctic is warming twice as fast as the rest of the planet, supplying the stream with increasingly warmer air.
“Heatwaves over northern hemisphere continents in recent years fit the hypothesis that rapid Arctic warming is playing a role,” says Francis.
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