Two months ago, France experienced its hottest May on record, with record highs in several cities. Last month, France was hit again by a spring heat wave that also affected Spain, Italy and other countries. Then, this month, Poland and other parts of Eastern Europe suffered a severe heatwave.
Now, temperatures across Europe are skyrocketing again, equaling or nearly tripling the numbers from Spain to the British Isles and spreading eastward. Wildfires burned by the heat fire in many countriesand most of the continent lies within prolonged drought.
And there are still two months of summer left.
Scientists say the persistent extreme heat this year is in line with the trend. They say heatwaves in Europe are increasing in frequency and intensity at a faster rate than most other regions of the planet, including the western United States.
Global warming plays a role, as in heatwaves around the world, as average temperatures are about 2 degrees Fahrenheit (1.1 degrees Celsius) higher than they were at the end of the 19th century, before carbon dioxide emissions and other gaseous heat traps became common. So extreme heat takes place from a higher starting point.
But beyond that, there are other factors, some related to atmospheric and ocean circulation, that could make Europe a heatwave hotspot.
No two heat waves are exactly alike. The current incineration temperature has reached into England and Wales on Monday, partly because an area of upper-level low-pressure air has been stagnant off the coast of Portugal for several days. It’s called the “low threshold” in the words of atmospheric scientists, because it’s cut off from the westerly river, the mid-latitude jet stream that surrounds the planet at high altitudes.
Areas of low pressure tend to draw air towards them. In this case, the low pressure area was continuously drawing air from North Africa towards it and into Europe. “It’s pumping hot air northward,” said Kai Kornhuber, a researcher at the Lamont-Doherty Earth Observatory at Columbia University.
Dr. Kornhuber has contributed to a Research published this month found that European heatwaves have increased in frequency and intensity over the past four decades, and related this increase at least in part to changes in jet streams. The researchers found that many European heatwaves occur when the jet stream temporarily splits in two, leaving an area of weak winds and high pressure air between the two arms leading to extremely high heat accumulations .
Efi Rousi, a senior scientist at the Potsdam Institute for Climate Research in Germany and lead author of the study, said the current heat wave appears to be related to a “dual jet”, which she said was done in Europe to last two weeks. This could lead to the creation of a low threshold, as well as an area of weak winds across Europe that allows the heat to linger, Dr Rousi said.
“It seems like this is really beneficial for the build-up of this heatwave,” she said.
There may be other reasons why Europe is seeing more, and more persistent, heatwaves, although some of these are currently the subject of debate among scientists. Natural climate variability can make it difficult to pinpoint specific effects, says Dr. Rousi.
Dr Kornhuber said warming in the Arctic, which is happening much faster than in other parts of the world, could play some role. As the Arctic warms at a faster rate, the temperature difference between it and the Equator decreases. This results in a reduction in summer winds, which has the effect of making weather systems last longer. “We see increased persistence,” he said.
There are also signs of a change in one of the world’s great ocean currents, Cycle that reverses the Atlantic meridian, which can affect the climate of Europe. Dr Rousi published a paper last year showing, using computer simulations, that the weakening of electric currents as the world warms will cause changes in atmospheric circulation leading to dry summers. than in Europe.
As elsewhere in the world, a heatwave in Europe could make it more likely elsewhere in the same region, because a period of extreme heat dries out 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 a heatwave wipes out most of the soil’s moisture, only a little is left to evaporate when the next heat wave arrives. So more of the sun’s energy is deposited on the surface, adding to the heat.
Raymond Zhong contribution report.
