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1、polaricecapmeltingpolaricecappolaricecapmeltingeffectscausessolutionsHowdotheyform?Athigherlatitudes,theearthdoesn’treceivemuchsunlightand,thereforethetemperaturesremainlowformostpartoftheyear,thusthewatercan’tremaininliquidformanditsolidifiesi.e.turnsintoice.Incaseofourownplane
2、t:thenorthernandthesouthernpolesarewheretheicecapsarelocated.Earth'snorthpoleiscoveredbyfloatingpackice(seaice)overtheArcticOcean.Portionsoftheicethatdon'tmeltseasonallycangetverythick,upto3–4metersthickoverlargeareas,withridgesupto20metersthick.One-yeariceisusuallyaboutameterth
3、ick.Theareacoveredbyseaicerangesbetween9and12millionkm².ThelandmassoftheEarth'ssouthpole,inAntarctica,iscoveredbytheAntarcticicesheet.Itcoversanareaofabout14.6millionkm²andcontains25-30millionkm³ofice.Around70%ofthefreshwaterontheEarthisheldinthisicesheet.TheIceIsMeltingByBANKI-
4、MOONPublished:September17,2009NewYorkTimesTwoweeksago,IvisitedtheArctic.Isawtheremainsofaglacierthatjustafewyearsagowasamajestic(宏伟的)massofice.Ithadcollapsed.Notslowlymelted—collapsed.Itraveledninehoursbyshipfromtheworld’snorthernmostsettlementtoreachthepolaricerim.Injustafewyea
5、rs,thesameshipmaybeabletosailunimpeded（畅通无阻的）allthewaytotheNorthPole.TheArcticcouldbevirtuallyice-freeby2030.Iwasalarmedbytherapidpaceofchangethere.Worsestill,changesintheArcticarenowacceleratingglobalwarming.Thawingpermafrostisreleasingmethane,agreenhousegas20timesmorepowerfult
6、hancarbondioxide.MeltingiceinGreenlandthreatenstoraisesealevels.CAUSESgeologicalchangesseasonalchangesglobalwarminggeologicalchangesThecausesforthesechangescanbeexplainedbyMilankovitchCycles.Thecyclesproposedbyhimtakeintoaccountorbitalshapes(eccentricity偏心率),axialtilt轴倾角(obliqui
7、ty倾角),axialprecession岁差,apsidalprecessionandorbitalinclination倾角.Allthesefactors,whencombined,affecttheconditionsontheplanetinthelongtermanditcausesiceagesatdifferenttimes.Duringaniceagetheicecapsincreaseinsizeandtheyretreatwhenaniceageends.Thesechangesoccuroveraperiodrangingfro
8、mthousandstomillionsofyears.seasonalchangesThey
