Changes in the pattern of the jet stream are halting severe weather patterns for days, or even weeks, and increasing the likelihood that large loss events will occur, according to a report released by Munich Re on Tuesday.
Intense flood events, longer crop-destroying droughts and more destructive winter storms are the most likely outcome as severe weather systems stall over regions rather than being quickly moved out by an ever weakening jet stream, the German reinsurance firm says.
“[The pattern] is reducing the differences in temperature and pressure between high latitudes and mid-latitudes, with the result that more frequent quasi-stationary weather patterns occur, “ the report published by Munich Re’s Topic GEO said. “Under such conditions, heat or drought and rain can assume extreme forms.”
In addition to spring and summer storms, Munich Re also tied the “persistence” issue to the current winter snowfalls that have crippled the Northeast U.S. this year and flood events in Europe in 2014.
The “consistent pattern of the jet stream” that resulted in storms produced $4 billion in insured losses in winter storm losses in North America and $1.5 billion in flood losses in the U.K. , the report states.
“The persistent weather patterns are caused by uncommonly stationary waves of the jet stream, a band of strong, high-altitude winds, that separate the cold Arctic and warm subtropical air masses,” said Peter Höppe, head of Geo Risks Research at Munich Re in a statement. “‘Troughs’ and ‘ridges’ of the jet stream bulging to the south or north, are responsible for events such as the long winter in North America in 2014. But persistent heavy rainfall or heat waves in the summer months can also be traced back to the phenomenon.”
The cause of the change and the jet stream, and the resulting increase in persistence, is the slow increase in the warming if the Arctic, says Dr. Jennifer Francis, research professor in the Department of Marine and Coastal Sciences at Rutgers University. Francis explains that the difference between the Arctic and warmer climates is what fuels the jet stream, and as the Arctic warms — and the difference in temperatures narrows — the jet stream “waves” lose force and becomes larger and slower.
“Its those waves in the jet stream create the weather, and when those waves get bigger basic atmospheric dynamic theory tells us they move more slowly,” she explained. “So the weather that we have is going to stick around longer.”
Munich Re’s Hoppe, however, hedge the climate change causation of persistent weather patterns in his statement.
“It is not yet possible to produce causal proof, but there is a logical chain of indices”, Höppe stated,” Hoppe said.