Weakening of summer storm intensifies heat extremes

The weakening of strong winds associated with the jetstream and weather systems prolongs and hence intensifies heat extremes like the one in Russia in 2010 which caused devastating crop failures and wildfires. They link the findings to changes in the Arctic caused by man-made global warming.

Lead-author Dim Coumou said that when the great air streams in the sky above us get disturbed by climate change, this can have severe effects on the ground. While you might expect reduced storm activity to be something good, it turns out that this reduction leads to a greater persistence of weather systems in the Northern hemisphere mid-latitudes.

Coumou added that in summer, storms transport moist and cool air from the oceans to the continents bringing relief after periods of oppressive heat. Slack periods, in contrast, make warm weather conditions endure, resulting in the buildup of heat and drought.

Co-author Jascha Lehmann added that unabated climate change will probably further weaken summer circulation patterns, which could thus aggravate the risk of heat waves. Remarkably, climate simulations for the next decades, the CMIP5, show the same link that they found in observations. So the warm temperature extremes they've experienced in recent years might be just a beginning.

Coumou noted that the heat extremes do not just increase because people are warming the planet, but because climate change disturbs airstreams that are important for shaping the weather. The reduced day-to-day variability that they observed makes weather more persistent, resulting in heat extremes on monthly timescales. So the risk of high-impact heat waves is likely to increase.

The study is published in the renowned journal Science.