In 1374, famines struck what is now Spain, Italy, and France. The culprit? The North Atlantic jet stream, a river of fast-moving air that flows from North America to Europe, had shifted north. The jet stream carries moisture-laden storm clouds, and without them, southern Europe was left dry, and crops died off.
Research published this week in the Proceedings of the National Academy of Sciences reconstructed a history of the jet stream’s path in the North Atlantic from the 700s AD to 2000. The findings suggest that, although climate change hasn’t altered the location of the crucial climate system yet, high emissions could push Europe into a world more like 1374.
Wiggles in the jet stream have been implicated in extreme weather over the past year, from the floods in Europe this spring to the heat wave that struck the Pacific Northwest, although the climate’s role in those movements is still an open question.
“The jet stream is this wavy, buckling band of wind, but the mean position changes over longer time scales,” says Matthew Osman, a climatologist at the University of Arizona, and lead author on the study.
The jet stream is held in place by polar air to the north and wind from the tropics to the south. And it pushes surface-level storms in its path, in what’s known as the storm track, reshaping rainfall across huge regions. “When the jet stream or storm track is situated further south, the already semi-arid regions of southern Europe receive a lot of moisture and mild temperatures,” says Osman. “But as the jet stream moves away towards the north, it takes away the storm track and precipitation and brings it to northern Europe.”