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1、智课网TOEFL备考资料托福阅读机经背景复习：温室气流全球变暖指的是在一段时间中，地球的大气和海洋温度上升的现象，主要是指人为因素造成的温度上升。原因很可能是由于温室气体排放过多造成。Thegreenhouseeffectistheprocessbywhichabsorptionandemissionofinfraredradiationbygasesintheatmospherewarmaplanet’sloweratmosphereandsurface.ItwasdiscoveredbyJosephFourieri
2、n1824andwasfirstinvestigatedquantitativelybySvanteArrheniusin1896.Existenceofthegreenhouseeffectassuchisnotdisputed,evenbythosewhodonotagreethattherecenttemperatureincreaseisattributabletohumanactivity.Thequestionisinsteadhowthestrengthofthegreenhouseeffectchang
3、eswhenhumanactivityincreasestheconcentrationsofgreenhousegasesintheatmosphere.Naturallyoccurringgreenhousegaseshaveameanwarmingeffectofabout33°C(59°F).[20]Themajorgreenhousegasesarewatervapor,whichcausesabout36–70percentofthegreenhouseeffect;carbondioxide(CO2),w
4、hichcauses9–26percent;methane(CH4),whichcauses4–9percent;andozone(O3),whichcauses3–7percent.Cloudsalsoaffecttheradiationbalance,buttheyarecomposedofliquidwateroriceandsoareconsideredseparatelyfromwatervaporandothergases.HumanactivitysincetheIndustrialRevolutionh
5、asincreasedtheamountofgreenhousegasesintheatmosphere,leadingtoincreasedradiativeforcingfromCO2,methane,troposphericozone,CFCsandnitrousoxide.TheconcentrationsofCO2andmethanehaveincreasedby36%and148%respectivelysincethemid-1700s.[24]Theselevelsaremuchhigherthanat
6、anytimeduringthelast650,000years,theperiodforwhichreliabledatahasbeenextractedfromicecores.LessdirectgeologicalevidenceindicatesthatCO2valuesthishighwerelastseenabout20millionyearsago.[26]Fossilfuelburninghasproducedaboutthree-quartersoftheincreaseinCO2fromhuman
7、activityoverthepast20years.Mostoftherestisduetoland-usechange,particularlydeforestation.CO2concentrationsarecontinuingtoriseduetoburningoffossilfuelsandland-usechange.Thefuturerateofrisewilldependonuncertaineconomic,sociological,technological,andnaturaldevelopme
8、nts.Accordingly,theIPCCSpecialReportonEmissionsScenariosgivesawiderangeoffutureCO2scenarios,rangingfrom541to970ppmbytheyear2100.Fossilfuelreservesaresufficienttoreach
