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1、ClimatechangeintheArcticBeatingaretreatArcticseaiceismeltingfarfasterthanclimatemodelspredict.Why?Sep24th2011ONSEPTEMBER9th,attheheightofitssummertimeshrinkage,icecovered4.33msquarekm,or1.67msquaremiles,oftheArcticOcean,accordingtoAmerica’sNationalSnowandIceDataCentre(NSIDC).Thatisnotarec
2、ordlow—notquite.Buttheactualrecord,4.17msquarekmin2007,wastheproductofanunusualcombinationofsunnydays,cloudlessskiesandwarmcurrentsflowingupfrommid-latitudes.Thisyearhasseennosuchoppositeofaperfectstorm,yetthesummersea-iceminimumisamere4%biggerthanthatrecord.Addinthefactthatthethicknessof
3、theice,whichismuchhardertomeasure,isestimatedtohavefallenbyhalfsince1979,whensatelliterecordsbegan,andthereisprobablylessicefloatingontheArcticOceannowthanatanytimesinceaparticularlywarmperiod8,000yearsago,soonafterthelasticeage.ThatArcticseaiceisdisappearinghasbeenknownfordecades.Theunde
4、rlyingcauseisbelievedbyallbutahandfulofclimatologiststobeglobalwarmingbroughtaboutbygreenhouse-gasemissions.Yettheratetheiceisvanishingconfoundstheseclimatologists’models.Thesepredictthatifthelevelofcarbondioxide,methaneandsoonintheatmospherecontinuestorise,thentheArcticOceanwillbefreeoff
5、loatingsummericebytheendofthecentury.Atcurrentratesofshrinkage,bycontrast,thislookslikelytohappensometimebetween2020and2050.ThereasonisthatArcticairiswarmingtwiceasfastastheatmosphereasawhole.Someofthecausesofthisareunderstood,butsomearenot.Thedarknessoflandandwatercomparedwiththereflecti
6、venessofsnowandicemeansthatwhenthelattermelttorevealtheformer,theareaexposedabsorbsmoreheatfromthesunandreflectslessofitbackintospace.Theresultisafeedbackloopthataccelerateslocalwarming.Suchfeedback,though,doesnotcompletelyexplainwhatishappening.Hencethesearchforotherthingsthatmightassist
7、theice’srapiddisappearance.ForcingtheissueOneisphysicalchangeintheiceitself.Formerlyasolidmassthatmeltedandrefrozeatitsedges,itisnowthinner,morefractured,andsomoreliabletomelt.Butthatis(literallyandfiguratively)amarginaleffect.Fillingthegapbetweenmodelandrealitymayn
