Oct 29, 2010

Forecast: global warming may bring giant drought

Thanks to glob­al warm­ing, the Un­ited States and many oth­er pop­u­lous coun­tries face a grow­ing threat of long, harsh drought in the next 30 years, a new study in­di­cates.

If the pro­jec­tions “come even close to be­ing real­ized, the con­se­quenc­es for so­ci­e­ty world­wide will be enor­mous,” said Aiguo Dai of the U.S. Na­tional Cen­ter for At­mos­pher­ic Re­search in Boul­der, Co­lo., who con­ducted the re­search.

Projected drought con­di­tions at this cen­tury's end, ac­cord­ing to a new study. (Cour­tesy NCAR).

His anal­y­sis con­cludes that glob­al warm­ing will likely cre­ate in­creas­ing dry­ness across much of the globe, pos­sibly reach­ing a scale in some re­gions by the cen­tu­ry’s end rare­ly, if ev­er, seen in mod­ern times.

Us­ing an en­sem­ble of 22 com­put­er cli­mate mod­els and a com­pre­hen­sive in­dex of drought con­di­tions, as well as anal­y­ses of pre­vi­ously pub­lished stud­ies, Dai re­ports that by the 2030s, dry­ness is likely to in­crease sub­stanti­ally across most of the West­ern Hem­i­sphere, along with large parts of Eur­a­sia, Af­ri­ca, and Aus­tral­ia.

In con­trast, higher-latitude re­gions from Alas­ka to Scan­di­na­via are likely to be­come moister, but not enough to bal­ance out the dry­ing else­where, Dai pre­dicts.

Dai cau­tioned that the find­ings are based on the best cur­rent pro­jec­tions of emis­sions of green­house gas­es, which trap heat in the at­mos­phere. What hap­pens will de­pend on many fac­tors, in­clud­ing nat­u­ral cli­mate cy­cles such as El NiƱo.

The find­ings ap­pear this week as part of a long­er pa­per in the re­search jour­nal Wi­ley In­ter­dis­ci­plin­ary Re­views: Cli­mate Change. The study was sup­ported by the U.S. Na­tional Sci­ence Founda­t­ion.

“This re­search does an ex­cel­lent job of plac­ing fu­ture warm­ing-induced drought in the con­text of the his­tor­i­cal drought record,” said Er­ic DeWeaver, pro­gram di­rec­tor in founda­t­ion’s Di­vi­sion of At­mos­pher­ic and Geo­space Sci­ences. “The work ar­gues credibly that the worst con­se­quenc­es of glob­al warm­ing may come in the form of re­duc­tions in wa­ter re­sources.”

While re­gion­al cli­mate pro­jec­tions are less cer­tain than those for the globe as a whole, Dai’s study in­di­cates that most of the west­ern two-thirds of the Un­ited States will be sig­nif­i­cantly dri­er by the 2030s. Oth­er places predicted to face a sig­nif­i­cant dry­ing threat in­clude much of Lat­in Amer­i­ca, in­clud­ing large sec­tions of Mex­i­co and Bra­zil; re­gions bor­der­ing the Med­i­ter­ra­nean Sea, which could be­come es­pe­cially dry; large swaths of South­west Asia; most of Af­ri­ca and Aus­tral­ia, with par­tic­u­larly arid con­di­tions in re­gions of Af­ri­ca; and South­east Asia, in­clud­ing parts of Chi­na and neigh­bor­ing coun­tries.

The study al­so finds that drought risk can be ex­pected to de­crease this cen­tu­ry across much of North­ern Eu­rope, Rus­sia, Can­a­da, and Alas­ka, as well as some ar­eas in the South­ern Hem­i­sphere. But “the in­creased wet­ness over the north­ern, sparsely pop­u­lated high lat­i­tudes can’t match the dry­ing over the more densely pop­u­lated tem­per­ate and trop­i­cal ar­eas,” Dai said.

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