Weather pat­terns that bring heat more fre­quent: study


Daily weather pat­terns have changed in re­cent decades, mak­ing eastern North Amer­ica, Europe and western Asia more prone to nas­tier sum­mer heat waves that go be­yond global warm­ing, a new U.S. study finds.

A team of cli­mate sci­en­tists at Stan­ford Univer­sity in Cal­i­for­nia looked at weather pat­terns since 1979 and found changes in fre­quency and strength in parts of the world, ac­cord­ing to a study pub­lished in the jour­nal Na­ture on Wed­nes­day. These are the types of weather pat­terns with sta­tion­ary high and low pres­sure sys­tems that you see on weather fore­casts, which is dif­fer­ent than grad­ual warm­ing from man­made cli­mate change.

The team stud­ied the kind of up­per air pat­terns that “sort of am­pli­fies the warm­ing trend,” said study lead au­thor Daniel Hor­ton.

The study doesn’t at­tempt to ex­plain why these changes are hap­pen­ing. But in gen­eral they fit a the­ory that has gained momen- tum in cli­mate science that says melt­ing sea ice in the Arc­tic has some­times al­tered the way the jet stream flows, con­tribut­ing to ex­treme weather such as deadly storms and hur­ri­canes, out­side ex­perts said.

In many cases, in­clud­ing the eastern U.S. and western Asia in sum­mer, some of these changes have be­come even more no­tice­able since 1990, the same pe­riod in which Arc­tic sea ice has gone through a rapid de­cline, the study found.

“There are more of them each sum­mer and on av­er­age they are last­ing longer and the long­est are last­ing longer,” Hor­ton said.

That pat­tern shift is even stronger in the sum­mer in Europe and western Asia, Hor­ton and co-au­thor Noah Dif­f­en­baugh found.

The pat­terns Hor­ton and Dif­f­en­baugh stud­ied are dif­fer­ent from the one re­spon­si­ble for the cur­rent south­east­ern U. S. heat wave, Hor­ton said. But the weather pat­terns were the type re­spon­si­ble for heat waves that killed more than 50,000 peo­ple in western Rus­sia in 2010 and more than 70,000 peo­ple Europe in 2003, the study said.

In win­ter, weather pat­tern shifts have oc­curred that made ex­tremely cold snaps in cen­tral Asia even worse, Hor­ton said. But the study also found an in­crease in the weather pat­terns as­so­ci­ated with weaker ex­treme cold snaps in western Asian win­ters.

Dif­f­en­baugh said the changes could be a re­sult of ran­dom chance, or a side ef­fect of cli­mate change and melt­ing sea ice as oth­ers have the­o­rized.

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