两极冰川融化(polar-ice-cap-melting)

polaricecappolaricecapmeltingeffectscausessolutionsHowdotheyform?•Athigherlatitudes,theearthdoesn’treceivemuchsunlightand,thereforethetemperaturesremainlowformostpartoftheyear,thusthewatercan’tremaininliquidformanditsolidifiesi.e.turnsintoice.Incaseofourownplanet:thenorthernandthesouthernpolesarewheretheicecapsarelocated.•Earth'snorthpoleiscoveredbyfloatingpackice(seaice)overtheArcticOcean.Portionsoftheicethatdon'tmeltseasonallycangetverythick,upto3–4metersthickoverlargeareas,withridgesupto20metersthick.One-yeariceisusuallyaboutameterthick.Theareacoveredbyseaicerangesbetween9and12millionkm².•ThelandmassoftheEarth'ssouthpole,inAntarctica,iscoveredbytheAntarcticicesheet.Itcoversanareaofabout14.6millionkm²andcontains25-30millionkm³ofice.Around70%ofthefreshwaterontheEarthisheldinthisicesheet.•TheIceIsMelting•ByBANKI-MOON•Published:September17,2009NewYorkTimes•Twoweeksago,IvisitedtheArctic.Isawtheremainsofaglacierthatjustafewyearsagowasamajestic(宏伟的)massofice.Ithadcollapsed.Notslowlymelted—collapsed.Itraveledninehoursbyshipfromtheworld’snorthernmostsettlementtoreachthepolaricerim.Injustafewyears,thesameshipmaybeabletosailunimpeded（畅通无阻的）allthewaytotheNorthPole.TheArcticcouldbevirtuallyice-freeby2030.•Iwasalarmedbytherapidpaceofchangethere.Worsestill,changesintheArcticarenowacceleratingglobalwarming.Thawingpermafrostisreleasingmethane,agreenhousegas20timesmorepowerfulthancarbondioxide.MeltingiceinGreenlandthreatenstoraisesealevels.CAUSES•geologicalchanges•seasonalchanges•globalwarminggeologicalchanges•ThecausesforthesechangescanbeexplainedbyMilankovitchCycles.Thecyclesproposedbyhimtakeintoaccountorbitalshapes(eccentricity偏心率),axialtilt轴倾角(obliquity倾角),axialprecession岁差,apsidalprecessionandorbitalinclination倾角.•Allthesefactors,whencombined,affecttheconditionsontheplanetinthelongtermanditcausesiceagesatdifferenttimes.Duringaniceagetheicecapsincreaseinsizeandtheyretreatwhenaniceageends.Thesechangesoccuroveraperiodrangingfromthousandstomillionsofyears.seasonalchanges•Theyaremedium-termchangesandtheyoccureveryyear.Everyyearwiththecomingofthewinterseason,theicecapsbegintoexpandbuttheymeltagainwiththecomingofthesummerseasons.GlobalWarmingTherearemanycausesofthemeltingofthepolaricecapsandglobalwarming,someofwhicharenatural.However,theactivitiesofmanareresponsibleformuchoftherapidchangethatscientistsareseeing.Humankindengagesinamultitudeofactivitiesthathaveacceleratedtheprocessofglobalwarming.Mostpeopleknowthattheman-madeactivitythathasbeencitedasamajoracceleratorofglobalwarmingisthecombustionoffossilfuels,suchascoalandpetroleum.Industrialprocessesandtheoperationofpersonalmotorvehiclesallreleasevariousemissionsintotheair,includingcarbonmonoxide一氧化碳,hydrocarbons碳氢化合物,andlead铅,whichturntocarbondioxide.Miningactivitiesalsoreleasemethane甲烷intotheatmosphere,whichisagreenhousegasthatleadstoawarmingplanet.•Theoverpopulationoftheplanetisanotheractivitythathasacceleratedglobalwarming.Morepeopleontheplanetmeanstherearegreaterenergyrequirements,moretransportationandincreasedneedforfood.Becauseoftheneedforcheapgoodsduetotheamountofpeopleontheplanet,plasticgoodshavebeenconstructed,whicharenotbiodegradable.•Morepeoplealsomeansmorecarsandmorecarbonemissionsmovingintotheair.Themorepeoplethereare,themoreroomneedstobemadefortheworld’spopulation,whichleadstoexpansionintowild,naturalareas,likeforests,whichprotecttheplanet’sdelicatebalance.•Oneoftheleastwell-knowncausesofglobalwarmingisdeforestation.Becauseofman’scravingforspace,lumber,andbeef,manyoftheplanet’sforestshavebeendestroyed.Treeshavebeencutdowntobeusedforconstruction,inordertoclearroomfornewdevelopmentsorhouses,andtomakeroomforcattletograzeinordertosatisfythedemandforbeef,especiallyintheUnitedStates.•However,theforestsaroundtheplanethaveaprotectivepurpose,becausetheyproduceoxygenthatreducestheamountofcarbondioxideintheatmosphere.Whenforestsareslashedandburned,carbonemissionsskyrocket猛涨.Boththeactofburningtheseorganicmaterialsandthelossofthetreesspeedupglobalwarming.Effectsofmelting•TheArcticcouldseeice-freesummersbytheendofthe21stcenturyifthecurrentrateoficecapshrinkingcontinues,accordingtotheNaturalResourcesDefenseCouncil(NRDC).ThelargestblockoficeintheArcticisbreakingintopieces,andthesummerpolaricecaphasshrunksome20percentsince1979.Meltingicecapsaffectlocalresidentsandwildlife,andcouldhaveafar-reachingimpactworldwidethroughrisingsealevelsandglobaltemperaturesClimate•ResearchcarriedoutbyscientistsatNASA美国国家航空航天局showsthatmeltingicecapshaveaneffectontheEarth'sclimate.ThepolaricecapsthatcoverthetopandbottomoftheEarthreflectsunlightintospace.Whentheicecapsrecededuetomelting,thesunlightisabsorbedbytheoceanandlandinsteadofbeingreflectedbacktospace.Asaresult,theplanetbecomeswarmer,moreicemeltsandthecyclerepeatsitself.•TheEnvironmentalProtectionAgency(EPA)citesastudyonitswebsiteproducedbytheArcticCouncilwhichstatesthatinrecentdecadestheaveragetemperatureintheArctichasrisenatnearlydoubletherateoftemperatureselsewhereintheworld.Thiswarmingisevidencedbymeltingofglaciersandseaice,whichaffects