Jet stream changes could amplify weather extremes by 2060s

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View looking down an ice coring borehole atop the Greenland ice sheet Credit: Sarah Das/WHOI

New U.S. National Science Foundation-funded research provides insights into how the position and intensity of the North Atlantic jet stream has changed during the past 1,250 years. The findings suggest that the position of the jet stream could migrate outside of the range of natural variability by as early as the year 2060 under unabated greenhouse gas emissions, with potentially drastic weather-related consequences for societies on both sides of the Atlantic.

Led by Matthew Osman, a researcher at the University of Arizona Climate Systems Center, the study is published  in Proceedings of the National Academy of Sciences.

Familiar to air travelers flying between North America and Europe, the North Atlantic jet stream is the ribbon of prevailing westerly winds circling the Arctic. Often called the "polar jet," these high-altitude winds impact weather and climate across eastern North America and western Europe, accounting for between 10% and 50% of variance in annual precipitation and temperature in both regions. However, little is known about how the jet stream varied during the past, or how it might change in the future.

Osman's research team collected glacial ice core samples from nearly 50 sites spanning the Greenland ice sheet to reconstruct changes in windiness across the North Atlantic dating back to the eighth century.  The reconstructions suggest that natural variability has thus far masked the effect of human-caused warming on mid-latitude atmospheric dynamics across annual and longer timescales.

"For most places on Earth, direct climate observations typically do not span more than a few decades," Osman said. "So we haven't had a great sense of how or why the jet stream changes over longer periods of time. What we do know is that extraordinary variations in the jet stream can have severe societal implications, such as floods and droughts, due to the impacts on weather patterns. In terms of thinking about the future, we can now begin to use the past as a sort of prologue."

The work reveals that although natural variability has largely controlled the position of the North Atlantic jet stream, continued warming could cause significant deviations from the norm. Model projections forecast a northward migration of the North Atlantic jet stream under 21st-century warming scenarios. Such migration could render the jet stream significantly different within a matter of decades.

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