West Coast warming linked to naturally occurring changes

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NOAANat­u­ral­ly occur­ring changes in winds, not human-caused cli­mate change, are respon­si­ble for most of the warm­ing on land and in the sea along the West Coast of North Amer­i­ca over the last cen­tu­ry, a study has found.

The analy­sis chal­lenges assump­tions that the buildup of green­house gas­es in the atmos­phere has been a sig­nif­i­cant dri­ver of the increase in tem­per­a­tures observed over many decades in the ocean and along the coast­line from Alas­ka to Cal­i­for­nia.

Changes in ocean cir­cu­la­tion as a result of weak­er winds were the main cause of about 1 degree Fahren­heit of warm­ing in the north­east Pacif­ic Ocean and near­by coastal land between 1900 and 2012, accord­ing to the analy­sis of ocean and air tem­per­a­tures over that time. The study, con­duct­ed by researchers from the Nation­al Ocean­ic and Atmos­pher­ic Admin­is­tra­tion and the Uni­ver­si­ty of Wash­ing­ton, was pub­lished Mon­day by the Pro­ceed­ings of the Nation­al Acad­e­my of Sci­ences.

Nat­ur­al, wind-dri­ven cli­mate pat­terns in the Pacif­ic Ocean, such as El Niño and the Pacif­ic Decadal Oscil­la­tion, are already known to exert a pow­er­ful influ­ence on sea and land tem­per­a­tures over years and even decades.

This lat­est research shows that sim­i­lar changes in atmos­pher­ic and ocean cir­cu­la­tion can dri­ve trends that last a cen­tu­ry or longer, over­shad­ow­ing the effects of human-gen­er­at­ed increase in green­house gas­es, the study’s authors said.

Chang­ing winds appear to explain a very large frac­tion of the warm­ing from year to year, decade to decade and the long-term,” said study leader James John­stone, an inde­pen­dent cli­ma­tol­o­gist who did most of the work when he was at the Uni­ver­si­ty of Wash­ing­ton’s Joint Insti­tute for the Study of the Atmos­phere and Ocean.

When coastal wind speeds weak­en, they result in less evap­o­ra­tion from the sea sur­face and unusu­al­ly low pres­sure that alters ocean cur­rents and caus­es tem­per­a­tures to rise over time.

The study found that weak­en­ing winds account­ed for more than 80% of the warm­ing trend along the Pacif­ic North­west coast between Wash­ing­ton and North­ern Cal­i­for­nia. In South­ern Cal­i­for­nia, weak­er winds were respon­si­ble for about 60% of the increased warm­ing.