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1、ClimatechangeintheArcticBeatingaretreatArcticseaiceismeltingfarfasterthanclimatemodelspredict.Why?Sep24th2011ONSEPTEMBER9th,attheheightofitssummertimeshrinkage,icecovered4.33msquarekm,or1.67msquaremiles,oftheArcticOcean,accordingtoAmerica’sNationalSnowandIceDataCentre(NSIDC).
2、Thatisnotarecordlow—notquite.Buttheactualrecord,4.17msquarekmin2007,wastheproductofanunusualcombinationofsunnydays,cloudlessskiesandwarmcurrentsflowingupfrommid-latitudes.Thisyearhasseennosuchoppositeofaperfectstorm,yetthesummersea-iceminimumisamere4%biggerthanthatrecord.Addi
3、nthefactthatthethicknessoftheice,whichismuchhardertomeasure,isestimatedtohavefallenbyhalfsince1979,whensatelliterecordsbegan,andthereisprobablylessicefloatingontheArcticOceannowthanatanytimesinceaparticularlywarmperiod8,000yearsago,soonafterthelasticeage.ThatArcticseaiceisdis
4、appearinghasbeenknownfordecades.Theunderlyingcauseisbelievedbyallbutahandfulofclimatologiststobeglobalwarmingbroughtaboutbygreenhouse-gasemissions.Yettheratetheiceisvanishingconfoundstheseclimatologists’models.Thesepredictthatifthelevelofcarbondioxide,methaneandsoonintheatmos
5、pherecontinuestorise,thentheArcticOceanwillbefreeoffloatingsummericebytheendofthecentury.Atcurrentratesofshrinkage,bycontrast,thislookslikelytohappensometimebetween2020and2050.ThereasonisthatArcticairiswarmingtwiceasfastastheatmosphereasawhole.Someofthecausesofthisareundersto
6、od,butsomearenot.Thedarknessoflandandwatercomparedwiththereflectivenessofsnowandicemeansthatwhenthelattermelttorevealtheformer,theareaexposedabsorbsmoreheatfromthesunandreflectslessofitbackintospace.Theresultisafeedbackloopthataccelerateslocalwarming.Suchfeedback,though,doesn
7、otcompletelyexplainwhatishappening.Hencethesearchforotherthingsthatmightassisttheice’srapiddisappearance.ForcingtheissueOneisphysicalchangeintheiceitself.Formerlyasolidmassthatmeltedandrefrozeatitsedges,itisnowthinner,morefractured,andsomoreliabletomelt.Butthatis(literallyand
8、figuratively)amarginaleffect.Fillingthegapbetweenmodelandrealitymayn
