What is behind the heat waves in Europe?

Two months ago, France had its warmest May on record, with record highs in some cities. Last month, France again suffered from a spring heat wave that also affected Spain, Italy and other countries. Then, this month, Poland and other parts of Eastern Europe suffered through a severe heat wave.

Now temperatures across Europe are rising again, at or near triple digits from Spain to the British Isles and spreading east. Forest fires fueled by heat Burning in many countriesmuch of the continent in Long dry labors.

And there are still two months of summer left.

Scientists say the already persistent intense heat this year is in line with the trend. They say heat waves in Europe are increasing in frequency and intensity at a faster rate than almost any other part of the planet, including the western United States.

Global warming plays a role, as does heat waves around the world, because temperatures average about two degrees Fahrenheit (1.1 degrees Celsius) higher than they were in the late 19th century, before carbon dioxide emissions and other global warming. The gases spread. So the intense heat radiates from a higher starting point.

But in addition to this, there are other factors, some related to the atmospheric and ocean cycle, that may make Europe a heatwave hot spot.

No two heat waves are exactly alike. The current scorching temperatures that have reached in England and Wales On Monday, it was partly because there was an area with low pressure air at a high level that had stopped off the coast of Portugal days ago. It’s known as “low cut” in the parlance of atmospheric scientists, because it was cut off by a river of westerly winds, the mid-latitudes jet stream, which circles the planet at high altitudes.

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Low pressure areas tend to draw air towards them. In this case, the area of ​​low pressure is steadily drawing air from North Africa towards it and into Europe. “It’s pumping hot air north,” said Kay Kornhuber, a researcher at the Lamont-Doherty Earth Observatory, part of Columbia University.

Dr. contributed Kornhuber in Study published this month which found that heat waves in Europe had increased in frequency and intensity over the past four decades, and linked the increase at least in part to changes in the jet stream. The researchers found that many European heat waves occurred when the jet stream temporarily split in two, leaving a region of weak winds and high-pressure air between the two branches leading to an accumulation of intense heat.

Effie Rossi, a senior scientist at the Potsdam Institute for Climate Research in Germany and the study’s lead author, said the current heat wave appears to be associated with such a “double jet”, which she said has been over Europe for the past two weeks. Dr Rossi said this could create a depression, as well as an area of ​​weak winds over Europe that allowed the heat to continue.

“This really does seem to favor the build-up of this heat wave,” she said.

There may be other reasons why Europe is experiencing more heat waves, and more constant ones, although some of these waves are currently under debate among scientists. Dr. Rossi said natural climate fluctuations can make it difficult to extrapolate specific effects.

Dr Kornhuber said warming in the Arctic, which is occurring much faster than in other parts of the world, may play a role. As the Arctic is warming at a faster rate, the temperature difference between it and the equator is decreasing. This results in a decrease in summer winds, which makes weather systems stay in place for longer. “We are seeing an increase in persistence,” he said.

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There are also indications of changes in one of the world’s major ocean currents, The rotation of the Atlantic meridian inversion, may affect the climate of Europe. Dr. Rossi published a research paper last year that showed, using computer simulations, that a weakening current as the world warms would cause changes in atmospheric circulation resulting in a summer drought in Europe.

As in other parts of the world, a heat wave in Europe can increase the likelihood of others in the same area, because a period of intense heat dries up the soil.

When there is some moisture in the soil, some of the sun’s energy is used to evaporate the water, resulting in a slight cooling effect. But when one heat wave wipes out nearly all of the soil’s moisture, there is little left to evaporate when the next wave of hot air arrives. So more of the sun’s energy bakes the surface and increases heat.

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