Status: 05.07.2022 3:52 p.m
Severe heat waves have increased worldwide in recent decades – but especially in Europe. According to a new study, this is due to changes in the so-called jet stream – large wind bands five to ten kilometers up.
In the entire northern hemisphere, Europe is most severely affected by stronger heat waves. Heat waves over Europe grew three to four times faster than in other northern mid-latitudes such as the United States or Canada. This is the result a study by the Potsdam Institute for Climate Impact Research (PIK).
These extreme hot spells are related to double jet streams and their increasing duration over Eurasia. Jet streams are large bands of wind at an altitude of five to ten kilometers. An international team of researchers evaluated observation data from the past 40 years.
Double jet streams ensure periods of extreme heat
These are states in which the jet stream splits into two branches. The longer duration works in addition to the rise in temperature from human-caused warming and leads to more intense heat waves, the researchers explained. Almost the entire upward trend in heat waves in Western Europe and about 30 percent in Europe as a whole can be explained with these double jet conditions, it said.
According to the researchers, one possible explanation for the increasing duration of the jet streams is the increased warming of the high latitudes, especially over land regions such as Siberia, northern Canada and Alaska. In the summer, these regions would have warmed much faster than the Arctic Ocean.
Extreme heat more frequent and intense
This increasing temperature difference between land and ocean favors the persistence of double-jet conditions in summer. Referring to Western Europe, PIK’s Efi Rousi, lead author of the study, said: “In this region, which coincides with the exit of the storm track moving from the North Atlantic to Europe, the weather systems usually come from the Atlantic and therefore have a cooling effect. If it but comes to the double jet, weather systems will be deflected north and sustained heat waves may develop over western Europe.” This is in contrast to other European regions.
Summer heat waves are not in themselves a new phenomenon. What is new, however, is that extreme heat events in Europe have occurred more frequently and more intensely in recent years. “We expect it to get worse,” said Rousi. A severe drought that has been going on for months is currently causing problems in Spain and Portugal. Italy has been suffering from drought and high temperatures for weeks.
Rousi emphasized: “Even if the topic requires further research, one thing is clear: double jet streams and their increasing residence time are the key to understanding the current and future heat wave risks over western Europe.”