Scientists have understood a great deal about climate change. But curiously, these extreme temperatures over several days in a row still partly escaped them. The new element concerns the atmospheric circulation, the circulation of the air. A study by a team of German, American and Dutch researchers published in Nature calls into question the phenomenon of “double jet stream” more frequent in the summer.
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Europe has always been caught in a pincer movement between the warm air of the Sahara which rises and the polar cold of the Arctic which descends. As long as the cold was cold, everything was fine. About 10 km above our heads, the jet stream came in from the Atlantic (from West to East) and gently swept the excessively hot air. The problem: it’s that the cold of the Far North isn’t so cold anymore! Today the region that is warming the most is Greenland, which is melting at a dizzying speed. The temperature difference between the hot current which rises and the cold current which descends is no longer sufficient. Consequence: the jet stream slows down, softens and the heat of the Sahara is no longer sufficiently repelled, it stagnates above our heads. That’s it “double jet stream” which causes these extreme temperatures. François Gemenne, who is one of the authors of Intergovernmental Panel on Climate Change (IPCC), summarizes the situation in the following way: we find ourselves in fact with a double effect of global warming. Temperatures are rising – that’s global warming. But in addition, the atmospheric air cools less, so it rises again.
The other continents obviously do not have a comparable zone to the south of their home. The United States and Canada do not have the air of the Sahara which comes to warm them so much, the same thing for Russia on the other side. As a result, according to the researchers of this study, the number of cumulative heat wave days increases by 0.6 days every decade in Europe, while for the rest of the middle latitudes it is +0.2. Clearly, heat waves are progressing three times faster in Europe. And if we consider not the quantity but the intensity, there it is four times faster.
This gives all these national records broken this summer July 19: 40.3°C recorded at Connigsby in England, 40.2°C at Heathrow London airport. The next day: 35.1°C in the south of Scotland (it was 32.8°C the last national record), compared to Malilla in Sweden: 37.2°C. But also six records broken in Germany, where 40°C was exceeded for the first time in quite a few places. And on the Portuguese side, 45°C in the center and even 47°C in Pinhao in the north (near Porto).