6 July 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 engulfed Spain and Portugal and is spreading north and east is just the latest such event in Western Europe, which now experiences bouts of potentially deadly heat nearly every summer. This year, parts of the region suffered from intense heat before summer even started. Global warming has exacerbated heat waves in Europe and elsewhere, primarily because 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 widespread emissions of heat-trapping carbon dioxide began. But beyond this basic warming, other mechanisms lead to heat waves. In the current one, low pressure air in southern Europe is drawing warm air from the Sahara northwards. This area of low pressure is expected to shift north and east, bringing the warm air to France and Britain and parts of central Europe. A recent study confirmed that Western Europe has become what researchers call a heatwave hot spot over the past four decades, with events increasing in frequency and cumulative intensity (defined as heat exceeding a certain threshold). What’s more, according to the study, 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, especially the mid-latitude state, contributed to the accelerating heat wave trend in Western Europe. The jet stream is a river of fast westerly to easterly winds in the upper atmosphere. Sometimes it splits into two. Heat waves can develop in areas of weak winds and high pressure air, known as stalling highs, between the northern and southern flanks of the jet stream. The researchers found that these “twin jets” are increasing in frequency and lasting longer, and that these changes are responsible for the changes in heat waves. Efi Rousi, 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 highs could develop on their own and cause the jet stream to break up, he said, “or it could be the other way around, the jet stream breaks up for other reasons, and that allows blocking to develop. “We don’t know exactly what the trigger is,” added Dr. Rousey. See more
