Scientists Say A Fluctuating Jet Stream May Be Causing Extreme Weather Events

"A new study suggests that the polar jet stream has been fluctuating more than normal as it passes over the parts of the Northern Hemisphere, and that's affecting weather in Europe and North America."

"The jet stream is like a river of wind that circles the Northern Hemisphere continuously. That river meanders north and south along the way, however. When those meanders occur over the Atlantic and the Pacific Oceans, it can alter pressure systems and wind patterns at lower latitudes in Europe and North America. And that affects how warm or rainy it is on those continents."

"Researchers at the University of Arizona and the Swiss Federal Research Institute studied tree rings to get a fix on how widely and how often the jet stream meanders."

"Biologist Valerie Trouet took samples from four species of trees in Europe, including Scots pine, dating back to 1725. These revealed what kind of weather Europe had each year. And that helped them establish the normal pattern of the jet stream's fluctuations."