The patterns of Earth’s high winds have surprisingly widespread effects on life on the ground. A study in the journal Nature shows that when the summer jet stream over Europe veers north or south of its usual path, it brings weather extremes that can exacerbate epidemics, ruin crop harvests, and feed wildfires. “The jet stream has caused these extreme conditions for 700 years in the past without greenhouse gases,” said Ellie Broadman, a co-author of the study and a researcher at the University of Arizona. …For the recent study, a team of researchers… used data from tree rings to reconstruct the position of the jet stream over the last 700 years. Then they sought to understand how these shifts affected people, comparing the results to records on epidemics, crop yields, and wildfires. …“The big challenge now is to work out how we can really use this new information to test and improve our climate models”.