Never before have the effects of climate change been so close to our doorstep: dried up rivers in Italy, threatened crops in Germany and water rationing in France. In the entire northern hemisphere, Europe is hit the hardest by heat waves. Heat waves in Germany increased three to four times faster than in the other northern central latitudes such as in the USA or Canada, as the Potsdam Institute for Climate Impact Research (PIK) announced on Tuesday. These extreme hot spells are related to double jet streams and their increasing duration over Eurasia.
An international team of researchers evaluated observation data from the past 40 years and showed for the first time that this rapid increase is related to changes in the atmospheric circulation. The so-called jet stream, a fast-moving band of wind that flows around the northern hemisphere from west to east at an altitude of about ten kilometers, is changing.
Jetstream changes weather in Europe
States in which the jet stream splits into two branches and thus forms double jet layers did not increase in number, but persisted longer. According to the study, this explains almost without exception the increase in heat waves in Western Europe and the approximately 30 percent more heat waves in the entire European region.
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. This increasing temperature difference between land and ocean favors the persistence of double-jet conditions in summer.
Heat waves, drought and dry soil
In western Europe, the weather systems usually come from the Atlantic and therefore have a cooling effect. However, if the double jet does occur, the weather systems will be deflected northwards, experts say, and sustained heat waves could develop over western Europe. In other European regions, such as the Mediterranean and Eastern Europe, heat waves are more likely to be related to dry soils.
“Summer heat waves are not a new phenomenon per se – what is new is that extreme heat events have become more frequent and intense in Europe in recent years,” explained Efi Rousi, lead author of the study. From the point of view of the PIK scientist, “it can be expected that it will get even worse”.