What a summer! Germany felt in July and August, as a country on the Mediterranean sea. For weeks it rained practically, temperature records were broken. Meteorologists diagnosed the second-hottest summer since records began.

only in Central Europe, not groaning, But under extreme weather – but also, for example California in the USA, where it was also hot and dry, and thousands of fire-six million square kilometers of Land devastated. Japan experienced, however, after intensive rains, devastating Floods with hundreds of fatalities.

For the American climate researcher Michael Mann, all of these events have a common trigger: the to the North hemisphere, the Jetstream, the change in the summer of 2018, only a little Woe.

In the Video: The wavy Jetstream

National Ocean Service

Takes to the air flow approximately ten kilometers in height always the same way, then the weather changes. The high-pressure remain areas then nailed over Germany or California – it is always hot. And also low-pressure areas stay where they are, such as over Japan. There is record rainfall.

it is Believed the simulations carried out by man, together with colleagues, the climate change increases the risk for such extreme weather. According to the in the journal “Science Advances” published study, the risk for heat waves and extreme rain is rising up to the year 2100 by about 50 percent.

The scientists had evaluated measurement data of the Jet stream from the years 1979 to 2015. You looked at how often the Jetstream changed his position, so that a minimum of nine days, the same weather prevailed.

Events in the future

“These data show a definite increase in the number of such events,” said the man. In addition, previous analyses had shown a connection between global warming and a little variable Jetstream.

The researchers have studied the phenomenon now but also for the future – with elaborate simulations. “On average, we can say that such Events increase in the future,” says Kai grit Huber from the Potsdam Institute for climate impact research (PIK). “Currently, approximately six per year to ten in the year 2100.” This is according to the simulations, the most likely case.

However, the simulations are subject to uncertainties but also to a stronger increase in Supertotobet extreme weather conditions, a lower increase or even a decrease, however with a lower probability.

Also in the observational data, which show a slight increase, plug uncertainties: “You have to be in such Trends carefully,” stresses Kornhuber. “Because in the earth System variations occur regularly – for example, the phenomenon El Niño.” There are also variations that have taken place spaces in an even longer time. The study is a first step to explore the phenomenon further, the Potsdam scientists. “In principle, we expect, however, alone, the physics is quite clear that weather extremes are on the increase.”

downside

The Jetstream pressure differences between the warm Equator and the cold of the Arctic. In theory, it would flow from the Equator directly to the North. However, the earth’s rotation, and various disruptions to distract him, so that he flows in the shaft-shaped from the West to the East.

disturbances are, for example, a high mountains such as the Rocky Mountains, an extreme difference in temperature between land and sea, or instabilities in the atmosphere. Create the meandering movement – also Rossby waves. Sometimes the jet stream To power while Circling the Northern hemisphere, six to eight – and-down movements. Where the jet stream is blowing to the North-East, including a high-pressure area. Where it is blowing to the Southeast, is located below a Deep.

Normally, the Position of the Jet stream shifts again and again – for example because of atmospheric instability and with it the position of the lows and highs. Therefore, the weather changes in our part on a regular basis.

But global warming is changing these processes, researchers warn. “The temperature differences between the Land and the sea to rise”, explained Kornhuber. This disturbance could distract the Jetstream at this point, wave-shaped. “He takes more often the same way.” Result: The weather changes for several days or weeks. Extreme heat or prolonged rains may result, depending on where you are located.

Such a planetary wave events have been according to the researchers, is also a cause of the devastating forest fires in Canada in 2016, the Floods in Europe in 2013 and the heat wave in Russia in 2010. The heat wave stresses 2018 passe also in this pattern, was not, however, part of the now published study, because it was completed before the end of the summer, and Kornhuber.

Dimmed sun

The simulations showed, however, also an effect that could defuse the situation in the coming years, perhaps something. It is to do with aerosols. These arise, for example, in the combustion of coal and Oil dim, especially in the highly industrialized middle of the sun’s Broad light, and thus reduce locally the global warming.

there Are, however, less air pollution and less aerosols that are warming the mid-Latitudes, faster, and the temperature difference in the Arctic is reduced, which in turn affects the jet stream. And so, less aerosols reduce the simulations suggest that the probability that the described extreme weather events occur.

A coal exit would be worthwhile, therefore, equal to twice, says PIK-scientist Stefan Rahmstorf, co-author of the study. There would be less climate-damaging CO2 and less air pollutants.

Video: climate extreme – Why the weather is always unpredictable

Video BBC