Extreme summer heat on three continents has the same causes |  Now

Extreme summer heat on three continents has the same causes | Now

Not only in Europe, but also in Asia and North America, this summer is very hot. Heat waves on three continents are all linked: climate change is making summers hotter, while a ‘snaking jet stream’ is making the weather especially hot.

Although the Dutch heat record was not broken last Tuesday, records were set in France and the United Kingdom. It’s been over 40 degrees for the first time in England. Meanwhile, heat and drought in southern Europe led to massive forest fires.

This week, large parts of the US also had to deal with highs of 40 degrees. Heat warnings are in place for more than 100 million residents from coast to coast.

In Shanghai, the absolute record temperature of 40.9 degrees was equaled two weeks ago. Much of China has been hit by another heat wave this week. In the northwestern province of Xinjiang, there is even a flood warning due to rapidly melting glaciers.

Climate change is everywhere

Those heat waves are thousands of miles apart, yet they are all associated with the same two events.

The first, of course, is climate change. As average temperatures around the world are rising, average summer heat is increasing. Heat waves are also increasing. “That link is statistically proven everywhere,” says KNMI climate researcher Karin van der Wiel. “We can say very clearly that all heat waves today bear the imprint of climate change.”

Increasing drought is also contributing to the heat. If the soil is very dry, as it is currently in southern Europe, less solar energy is replaced by evaporation of water. Instead, the air is additionally heated, resulting in even higher temperatures.

Records are often ‘crushed’

Climate change also increases the likelihood of breaking temperature records in the event of a heat wave. Additionally, the possibility of records being ‘crushed’ increases. Meteorologists talk about this when the old record is exceeded by more than 1 degree. In the Netherlands, it happened in 2019, when a national record temperature of 40.7 degrees was recorded in Gils-Rijn.

According to calculations, the KNMI According to climate models, the temperature record has about a 2 percent chance of being broken in a year. At the turn of the last century, that chance was less than twice that. By 2060, models show that chance will increase to 3 percent from the present. Then, on average, temperature records are crushed every thirty years.

The jet stream is about to turn

But ‘general’ global warming is not the only cause of heatwaves being the most common. Changes in the jet stream can also contribute to the development of heat waves.

A jet stream is an air current at an altitude of about 10 kilometers that moves from west to east in the Northern Hemisphere. The jet stream sometimes ‘tightens’ and then blows it over the Atlantic Ocean to the Netherlands.

But if the jet stream is weak, it can cause ‘injury’. For example, he can ensure that warm air from North Africa, Spain and Portugal is brought north. This led to heatwaves in Western Europe last week. The twisting jet stream causes high and low pressure areas to persist for long periods of time, allowing warm air to stay in one place for days.

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The twisting jet stream causes long-term heat waves – or, in the case of the above scenario from 2021, very heavy rainfall in one place. At the time, a persistent low pressure area led to flooding in Limburg, Belgium and Germany.


The twisting jet stream causes long-term heat waves – or, in the case of the above scenario from 2021, very heavy rainfall in one place.  At the time, a persistent low pressure area led to flooding in Limburg, Belgium and Germany.

The twisting jet stream causes long-term heat waves – or, in the case of the above scenario from 2021, very heavy rainfall in one place. At the time, a persistent low pressure area led to flooding in Limburg, Belgium and Germany.

Photo: Bart-Jan Dekker, NU.nl

Europe gets more heat waves

The jet stream currently has seven twists and turns across the Northern Hemisphere, says Professor of Climate Extremes Tim Cuomo (VU Amsterdam). This pattern often warms Europe and North America in summer, and is currently leaving a warm patch over China.

Although the jet stream affects many places, its effect is greatest here. “In Europe, we see extreme temperatures increasing rapidly,” says Coumou.

Associated with a ‘double jet stream’ that hangs more and more across the continent in summer, Coumou and fellow scientists recently wrote in the journal Science. Natural communication. Relatively strong westerly winds blow over northern Scandinavia and over the Mediterranean.

“We see an increase in the double jet stream over the last 40 years,” says Coumou. But it’s still unclear whether the changes in the jet stream are due to climate change or something else. “We want to look at that in follow-up studies.”

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