专业英语温室效应ppt课件.ppt

UnitFour TheGreenhouseEffect 第四课温室效应 1 Newwords Triple三倍于quadruple四倍于NationalAcademyofScience国家科学院Impact影响effectFeedback反馈annual每年的Seasonal每季的Expand扩展extendspreadAntarctic南极洲Greenland格陵兰Flood洪水泛滥Bangladesh孟加拉BayofBengal孟加拉湾 BOB Timely定时的 及时的Zone区域region 2 Infraredradiation红外辐射Climaticfeedback气候反馈Snowcover雪盖Etal 等等 人 etc 等等 物 3 4 5 6 7 辐射 物体以电磁波或粒子流形式向周围传递或交换能量的方式 电磁波谱 辐射的基本知识 辐射是太阳能传输到地球的唯一途径 8 大气窗 7 13 9 大气中的辐射传输过程 大气对短波的影响 吸收散射反射 吸收逆辐射 大气对长波的影响 10 11 12 13 ppm partpermillion 14 15 P1 Manisreversingmillionsofyearsofnaturalevolutionbyputtingintotheatmospherecarbonthathadbeensequesteredovertheagesasfossilfuels AtmosphericconcentrationsofCO2arelikelytodouble andpossiblytriple by2100 Becausenohistoricalprecedentexists reasonableexpectationsaboutfutureclimatemustbebasedonscientificevidence notgeologicalrecords Afterevaluatingtheavailableevidence theNationalAcademyofSciencesconcludedthatadoublingofatmosphericconcentrationsofCO2wouldwarmtheearth saveragetemperature1 5 4 5 16 17 P2 Thegreenhouseeffectoftheatmospherehasneverbeendoubted Moreofthesun sradiationisvisiblelight whichpassesthroughtheatmospherelargelyundeterred Whentheradiationstrikestheearth itwarmsthesurface whichthenradiatestheheatasinfraredradiation However atmosphericCO2 watervapor andsomeothergasesabsorbtheinfraredradiationratherthanallowittopassundeterredlythroughtheatmospheretospace Becausetheatmospheretrapstheheatandwarmstheearthinamannersomewhatanalogoustotheglasspanelsofagreenhouse thisphenomenonisgenerallyknownasthe greenhouseeffect Withoutthiseffect theearthwouldbe33 60 colderthatitiscurrently 18 P3 TheextenttowhichCO2absorbsheathasbeenknownforalmostacentury ScientistsshowthatdoublingofatmosphericCO2wouldraisetheaveragetemperature1 2 ifnothingelseintheearth sclimaticsystemchanged However manypartsoftheclimatewillchange amplifyingthedirectimpactofCO2 Becausethesechangesarenotcompletelyunderstood thetotalwarmingisdifficulttoestimate ThecurrentuncertaintysurroundingtheimpactofCO2onaveragetemperatureiscenteredaroundtheseclimatic feedback notthedirectwarmingfromCO2 19 P4 Themostimportantfeedbackwillresultfromthewarmeratmosphere sabilitytoretainmoisture Becausewatervaporalsoabsorbsinfraredradiation additionalheatingwillresult Hansoneral estimatethatdoubleCO2wouldincreasetheatmosphere swatervaporcontent30 heatingtheearthandadditional1 4 20 P5 Anotherimportantpositivefeedbackconcernstheimpactofsnowandicecoverontheearth salbedo theextenttowhichitreflectssunlight Iceandsnowreflectmostofthesun sradiation whilewaterandsoilabsorbit Anincreaseinsurfacetemperatureswouldmeltsnowonlandandfloatingiceandtherebyallowtheearthtoabsorbenergythatwouldotherwisebereflectedbackintospace Hansonetal estimateanadditionalwarmingof0 4 fromthealbedoeffect 21 P6 Afeedbackthatislessunderstoodistheimpactofaglobalwarmingonclouds whichalsoreflectsunlightintospace Theeffectsofcloudsontheearth salbedodependontheirheightsandotherproperties aswellastheextentofcloudcover Thus theimpactofaglobalwarmingoncloudsissomewhatuncertain Nevertheless withsomewhatlessconfidence Hansonetal estimatea2 reductionincloudcoverandaresultingwarmingof0 5 Theyalsoestimatethatincreaseincloudheightwouldresultinanadditionalwarmingof0 5 foratotalimpactof1 0 fromclouds 22 P7 AlthoughtheincreaseintheaveragetemperatureoftheearthisaconvenientshorthanddescriptionofCO2inducedclimatechange itmasksimportantregionalimplications Mostsearchersagreethatpolartemperaturewouldincreasetwotothreetimestheearth saverageincrease Theworld sclimatedependslargelyoncirculationpatternsbywhichtheatmosphereandtheoceanstransportheatfromwarmtocoldregions 23 P7 Asaresult anysignificantchangeinthedifferencebetweenequatorialandpolartemperaturescoulddramaticallyaffectclimaticpatterns Aparticularlyimportanteffectofthesechangeswillbeshiftsinannualandseasonalprecipitationandevaporation withsomeareasgainingandotherlosing Furthermore becausehurricanesrequireanoceantemperatureof27 orwarmer aglobalwarmingcouldallowhurricanestoformathigherlatitudesandduringagreaterpartoftheyear Thesechangescouldbeimportanttocoastalcommunities 24 P8 Amoreimmediate 直接的 concernisthattheprojectedglobalwarmingcouldraisetheseaasmuchasonemeterinthenextcenturybyheatingoceanwater whichwouldthenexpand andbycausingmountainglaciersandpartsoficesheetsinWestAntarctica EastAntarctica andGreenlandtomeltorslideintotheoceans Thus theseacouldreachheightsunprecedentedinthehistoryofcivilizationuntilthiseffort Noonehadattemptedtoforecastsealevelriseinspecificyearsordetermineitsimportancetotoday sactivities 25 P9 Ifthispredictioncomestrue thewaterwillfloodover15percentifBangladesh sterritory about12to15percentofEgypt scultivatedlandandsignificantlyreducetheterritoryofmanyislandcountries IntheUnitedStates thousandsofsquaremilesoflandcouldbelost particularlyinlow lyingareassuchastheMississippiDelta wherethelandisalsosubsidingatapproximatelyonemeterpercentury Stormdamage alreadyestimatedatoverthreebilliondollarsperyearnationwide couldalsoincreasethesalinityofmarshes estuaries andaquifers disruptingmarinelifeandpossiblythreateningsomedrinkingwatersupplies 26 Thegreenhousegasesarealsodamagingtheozonelayersurroundingtheearthwhichprotectshumanbeingsfromultravioletradiation Researchshowsthatcancercouldincreaseby3percentforevery1percentreductionintheozonelayer Fortunately themostadverse 不利的 effectscanbeavoidediftimelyactionsaretaken 27 P10 AlthoughtheclimaticchangesthatcouldresultfromCO2emissionsispoorlyunderstood thereiscompleteagreementthatCO2concentrationsareincreasing 28 P11 Approximatelyone halftheCO2releasedbycombustionoffossilfuelshasremainedintheatmosphere ItisgenerallybelievedthatmostoftheremainingCO2hasdissolvedintotheoceans AlthoughtropicaldeforestationandcementproductionalsoresultinCO2emission theircontributionhavebeenandwillcontinuetobemuchlessimportant 29 P12 Controllingthegreenhousegases especiallytheincreasingdischarge 排放 ofcarbondioxidehasalreadybecomeakeyproblem Theglobalcommunitymustmakeeffortstoreducethegreenhouseeffect 30 P13 Inthenextfewdecades however CO2emissionsareunlikelytobecurtailed eithervoluntarilyorbyregulation Theworld sinfrastructureisbuiltaroundfossilfuels Thecost 成本 ofusingcoal gasandoilislowcomparedwithnuclearandsolarpower andthisrelativecostadvantage 优势 isexpectedtocontinue Therefore avoluntaryreductioninCO2emissionsisunlikely 31 P14 TheonlygovernmentactionthatcouldsuccessfullyreduceCO2emissionswouldbetocurtailtheuseoffossilfuels EmissioncontrolsforCO2frompowerplants 电厂 wouldatleastquadruplethecostofelectricity Forsmallerusersoffossilfuels suchashomesandmotorvehicles controlisnotevenfeasible Otherplans suchassequesteringcarboninmassivetreeplantings areevenlessplausible 32 P15 Evenifpoliticalleadersdecidetotakedrastic 严厉的 actionstolimitworldwideconsumptionoffossilfuels itisprobablyalreadytoolatetopreventsignificantrisesinglobaltemperaturesandsealevel Arecentstudyinvestigatedtheimpactofdrasticenergypolicychangesontheexpectedtimingofagreenhousewarming SeidelandKeyes 1983 Theauthorsconcludedthatsuchpoliciescouldhaveimportantimpactby2100 butwouldnotsubstantiallydelaythe2 Cwarmingexpectedby2040 33 Theyestimatedthata300percenttaxonfossilfuelswoulddelaythe2Cwarmingbyonlyfiveyears andthatevenaworldwidebanoncoal shale 页岩 oil andsyntheticfuelswoulddelaythewarmingbyonlytwenty fiveyears ifimplementedby2000 Furthermore suchabanwoulddelaytheriseinsealevelexpectedthrough2040byonlytwelveyears 34 P16 Thepoliticalfeasibilityofinstituting 制定 suchabanby2000isalsodoubtful becauseonlyaworldwideagreementtocurtailemissioncouldbesuccessful AnyindividualnationthatcurtailsitsownemissionswilldelaythedaywhenCO2concentrationsdoublebyafewyearsatmost Furthermore becauseenergycostswouldincreaseforanynationthatcurtailsitsemissions thatnation sindustrieswouldbeplacedatacompetitivedisadvantagecomparedwiththoseoftherestoftheworld 35 Finally politicalleaderswouldrequireproofthatsuchapolicywouldbemorebeneficialthanadaptingtohigherCO2levels Suchproofwillprobablyremainimpossibletoprovidefortheforeseeablefut