A major new study explains why Western Europe has suffered through a series of extreme heat waves that are outpacing even the planet's overall warming trend.
Driving the news: The study points to stubborn changes in atmospheric circulation for much of the blame.
Why it matters: Heat waves are deadly. Increases in their frequency and intensity — already taking place due to global warming — raise these risks.
- But Western Europe has seen a sharp spike in heat waves during the past 42 years, with such events increasing three to four times faster than other parts of the Northern Hemisphere.
- Last week, areas from Italy to Norway saw monthly and all-time record high temperatures, which contributed to a deadly glacial avalanche in the Dolomite Mountains.
Zoom in: The new study, published in Nature Communications, finds that the upward trends in Western European heat waves are tied to the flow of air in the jet stream in and around the region.
- Specifically, the researchers found that a particular weather pattern, featuring two branches of fast-moving corridors of air across Eurasia, is most closely associated with Western European heat waves.
- These weather patterns favor weaker upper-level winds over Western Europe, and encourage long-lasting, blocking high-pressure areas, also known as heat domes.
- Increasingly persistent double jet stream patterns and their associated heat domes can explain "almost all of the accelerated trend" in heat waves across Western Europe, the study states.
The big picture: Importantly, the study ties the persistence of particular jet stream patterns and related heat domes to the rapidly warming land temperatures in the Arctic, and the growing contrast between land and ocean temperatures there.
- Such thermal gradients can influence weather patterns.
- The research also fits with prior studies of how simultaneous extreme heat events can develop in different parts of the world as climate change worsens.
Yes, but: The study cautions that there are still uncertainties regarding what is causing the increase in the occurrence and persistence of these particular weather patterns, noting that climate models may not be simulating them accurately.
What they're saying: "Climate models tend to underestimate extreme weather risks," said study co-author Kai Kornhuber of Columbia University, in a statement. "Projections of extreme heat under continued greenhouse gas emissions might be too conservative."
