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Jet stream changes since 1960s linked to more extreme weather Increased fluctuations in the path of the North Atlantic jet stream since the 1960s coincide with more extreme weather events in Europe such as heat waves, droughts, wildfires and flooding, reports a University of Arizona-led team.The research is the first reconstruction of historical changes in the North Atlantic jet stream prior to the 20th century. By studying tree rings from trees in the British Isles and the northeastern Mediterranean, the team teased out those regions' late summer weather going back almost 300 years—to 1725. "We find that the position of the North Atlantic Jet in summer has been a strong driver of climate extremes in Europe for the last 300 years," Trouet said.Having a 290-year record of the position of the jet stream let Trouet and her colleagues determine that swings between northern and southern positions of the jet became more frequent in the second half of the 20th century, she said. "Since 1960 we get more years when the jet is in an extreme position." Trouet said, adding that the increase is unprecedented.When the North Atlantic Jet is in the extreme northern position, the British Isles and western Europe have a summer heat wave while southeastern Europe has heavy rains and flooding, she said. When the jet is in the extreme southern position, the situation flips: Western Europe has heavy rains and flooding while southeastern Europe has extreme high temperatures, drought and wildfires. "Heat waves, droughts and floods affect people," Trouet said. "The heat waves and drought that are related to such jet stream extremes happen on top of already increasing temperatures and global warming—it's a double whammy. "Extreme summer weather events in the American Midwest are also associated with extreme northward or southward movements of the jet stream, the authors write. "We studied the summer position of the North Atlantic jet. What we're experiencing now in North America is part of the same jet stream system," Trouet said. This winter's extreme cold and snow in the North American Northeast and extreme warmth and dryness in California and the American Southwest are related to the winter position of the North Pacific Jet, she said. The paper, "Recent enhanced high-summer North Atlantic Jet variability emerges from three-century context," by Trouet and her co-authors Flurin Babst of the Swiss Federal Research Institute WSL in Birmensdorf and Matthew Meko of the UA is scheduled for publication in Nature Communications on Jan. 12. The U.S. National Science Foundation and the Swiss National Science Foundation funded the research.

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