July 6, 2022, 11:00 PM ET
6 Jul 2022 23:00 ETS Smoke and fire at O Barco de Valdeorras in the Galencia region of north-west Spain on Sunday. Extreme heat is fueling wildfires across the country. Credit…Brais Lorenzo/EPA, via Shutterstock
The extreme heat wave that has gripped Spain and Portugal and is spreading north and east is just the latest such event in western Europe, which now experiences periods of potentially deadly hot weather almost every summer. This year, parts of the region suffered from intense heat even before the start of summer.
Global warming has worsened heat waves in Europe and elsewhere for the main reason that they start from a higher-than-ever baseline temperature. Average global temperatures have risen by about 1.1 degrees Celsius (about 2 degrees Fahrenheit) since the late 19th century, when mass emissions of heat-trapping carbon dioxide began.
But beyond this baseline warming, other mechanisms drive heat waves. At present, low-pressure air in southern Europe is pulling hot air from the Sahara north. This area of low pressure is expected to move north and east, bringing the hot air into France and Britain and parts of central Europe.
A recent study confirmed that Western Europe has become what researchers call a heatwave hotspot over the past four decades, with events increasing in frequency and cumulative intensity (defined as heat exceeding a certain threshold).
What’s more, the study found that changes in frequency and intensity are happening faster in Europe than in many other parts of the world — including another hot spot, the Western United States.
The study, published this month in Nature Communications, found that atmospheric circulation, specifically the state of the midlatitude jet stream, contributed to the accelerating heat wave trend in western Europe.
The jet stream is a river of fast winds from west to east in the upper atmosphere. Sometimes it splits into two. Heat waves can develop in areas of weak winds and high air pressure, known as blocking tops, between the northern and southern flanks of the jet stream.
The researchers found that these “double jet” events are increasing in frequency and lasting longer, and that these changes account for changes in heat waves.
Effie Russi, a senior scientist at the Potsdam Institute for Climate Research in Germany and lead author of the study, said it was unclear what caused the jet stream to split. Blocking tips can develop on their own and cause the jet stream to split, she said, “or it could be the other way around that the jet stream splits for other reasons and that allows the blocking to develop.”
“We don’t know exactly what the trigger is,” added Dr. Russi.
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