Over decades, heat waves have increased faster over Europe than in the USA or Canada. According to one study, the extreme periods are related to double jet streams - wind bands several kilometers up. Because these last longer, Western Europe in particular is groaning under the heat.
According to Potsdam researchers, important factors for the increase in heat waves, especially in Western Europe, are changes in the so-called jet streams - large wind bands five to ten kilometers high. This is the result of a new study by an international team of researchers from the Potsdam Institute for Climate Impact Research (PIK), which appears in the journal "Nature Communications".
To do this, the scientists evaluated observation data from the last 40 years. The result: Over Europe, particularly western Europe, heat waves have increased three to four times faster than in the rest of northern mid-latitudes such as the United States or Canada. These extreme heat periods are therefore related to double jet streams and their increasing duration.
Such situations are considered to be conditions in which the jet stream splits into two branches. The researchers point out that the longer duration works in addition to the temperature increase caused by human-induced warming and leads to more intense heat waves. 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.
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.
Although summer heat waves are not a new phenomenon, what is new is that extreme heat events have occurred more frequently and more intensively in Europe in recent years. "We expect it to get worse," said Rousi.
According to the researchers, a possible explanation for the fact that double jets are so persistent is the increased warming of the high latitudes, especially over land regions such as Siberia, northern Canada and Alaska. 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."