An oppressive heat wave baked Western Europe this week, setting record high temperatures in France, Germany, Poland and the Czech Republic. In India, a severe drought has choked water supplies in the city of Chennai, exposing its 9 million residents to a major shortage. And after the United States’ wettest 12-month stretch on record, towns across the Midwest and the Great Plains are reeling from devastating floods, NBC News reports.
The reasons behind these extreme weather events are complex, but scientists believe they have a common trigger: profound recent changes to the jet stream, a ribbon of fast-moving air that flows from west to east over the Northern Hemisphere and controls weather systems.
Seasonal variations are normal, but since the early 2000s, as the planet has warmed, the jet stream has been behaving strangely. Jet stream winds, which naturally undulate, have become even more gnarled, and the big wavy patterns sometimes slow to a crawl, or even completely stall.
A sluggish jet stream is cause for concern. When it slows or gets stuck, high- or low-pressure weather systems that correspond to the jet stream’s ridges and troughs intensify, stretching out rainy episodes, heat waves or droughts for days — or even weeks — at a time. Studies suggest that climate change is driving these new patterns, which means extreme temperatures could be more common in the future.