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1、ClimatechangeintheArcticBeatingaretreatArcticseaiceismeltingfarfasterthanclimatemodelspredict.Why?Sep24th2011ONSEPTEMBER9th,attheheightofitssummertimeshrinkage,icecovered4.33msquarekm,or1.67msquaremiles,oftheArcticOcean,accordingtoAmerica’sNationalSnowandIceDataCentre(NSIDC).Thati
2、snotarecordlow—notquite.Buttheactualrecord,4.17msquarekmin2007,wastheproductofanunusualcombinationofsunnydays,cloudlessskiesandwarmcurrentsflowingupfrommid-latitudes.Thisyearhasseennosuchoppositeofaperfectstorm,yetthesummersea-iceminimumisamere4%biggerthanthatrecord.Addinthefactth
3、atthethicknessoftheice,whichismuchhardertomeasure,isestimatedtohavefallenbyhalfsince1979,whensatelliterecordsbegan,andthereisprobablylessicefloatingontheArcticOceannowthanatanytimesinceaparticularlywarmperiod8,000yearsago,soonafterthelasticeage.ThatArcticseaiceisdisappearinghasbee
4、nknownfordecades.Theunderlyingcauseisbelievedbyallbutahandfulofclimatologiststobeglobalwarmingbroughtaboutbygreenhouse-gasemissions.Yettheratetheiceisvanishingconfoundstheseclimatologists’models.Thesepredictthatifthelevelofcarbondioxide,methaneandsoonintheatmospherecontinuestorise
5、,thentheArcticOceanwillbefreeoffloatingsummericebytheendofthecentury.Atcurrentratesofshrinkage,bycontrast,thislookslikelytohappensometimebetween2020and2050.ThereasonisthatArcticairiswarmingtwiceasfastastheatmosphereasawhole.Someofthecausesofthisareunderstood,butsomearenot.Thedarkn
6、essoflandandwatercomparedwiththereflectivenessofsnowandicemeansthatwhenthelattermelttorevealtheformer,theareaexposedabsorbsmoreheatfromthesunandreflectslessofitbackintospace.Theresultisafeedbackloopthataccelerateslocalwarming.Suchfeedback,though,doesnotcompletelyexplainwhatishappe
7、ning.Hencethesearchforotherthingsthatmightassisttheice’srapiddisappearance.ForcingtheissueOneisphysicalchangeintheiceitself.Formerlyasolidmassthatmeltedandrefrozeatitsedges,itisnowthinner,morefractured,andsomoreliabletomelt.Butthatis(literallyandfiguratively)amarginaleffect.Fillin
8、gthegapbetweenmodelandrealitymayn