Passage2<br/><spanstyle="display:block;text-align:center;">InGreenland,IceandInstability</span>TheancientfrozendomecloakingGreenlandissovastthatpilotshavecrashedintowhattheythoughtwasacloudbankspanningthehorizon.Flyingoverit,youcanscarcelyimaginethatitcoulderodefastenoughtodangerouslyraisesealevelsanytimesoon.<br/>Alongtheflanksinspringandsummer,however,thepictureisverydifferent.Foranincreasingnumberofwarmyears,anetworkofbluelakesandrivuletsofmelt-waterhasbeenspreadingeverhigherontheicecap.<br/>Themeltingsurfacedarkens,absorbinguptofourtimesasmuchenergyfromthesunassnow,whichreflectssunlight.Naturaldrainpipescalledmoulinscarrywaterfromthesurfaceintothedepths,insomeplacesreachingbedrock.<br/>Theprocessslightly,butmeasurably,lubricatesandacceleratesthegrindingpassageoficetowardsthesea.<br/>Mostimportant,manyglaciologistssay,isthebreak-upofhugesemi-submergedclotsoficewheresomelargeGreenlandglaciers,particularlyalongthewestcoast,squeezethroughfiordsastheymeetthewarmingocean.Asthesepassageshavecleared,thishassharplyacceleratedtheflowofmanyofthesecreeping,corrugatedandfrozenrivers.<br/>Someglaciologistsfearthattheriseinseasinawarmingworldcouldbemuchgreaterthantheupperestimateofabout60centimetresthiscenturymadebytheIntergovernmentalPanelonClimateChangelastyear.(Seasroselessthan30centimetreslastcentury.)<br/>Thepanel’sassessmentdidnotincludefactorsknowntocontributetoiceflowsbutnotunderstoodwellenoughtoestimatewithconfidence.Ascientificscrambleisunderwaytoclarifywhethertheerosionoftheworld’smostvulnerableicesheets,inGreenlandandwestAntarctica,cancontinuetoaccelerate.Theeffortinvolvesfieldandsatelliteanalysesandsiftingforcluesfrompastwarmperiods.<br/>Thingsaredefinitelyfarmoreseriousthananyonewouldhavethoughtfiveyearsago.