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第PAGE\*MERGEFORMAT2页共NUMPAGES\*MERGEFORMAT2页 英语四级美文听力第95篇:HotterorColder? HotterorColder?Itwasoncethoughtthatairpollutionaffectedonlytheareaimmediatelyaroundlargecitieswithfactoriesand/orheavyautomobiletraffic.Today,weknowthatalthoughthesearetheareaswiththeworstairpollution,theproblemisliterallyworldwide.Onseveraloccasionsoverthepastdecade,aheavycloudofairpollutionhascoveredtheentireeasternhalfoftheUnitedStatesandledtohealthwarningseveninruralareasawayfromanymajorconcentrationofmanufacturingandautomobiletraffic.Infact,theclimateoftheentireearthmaybeaffectedbyairpollution.Somescientistsfeelthattheincreasingconcentrationofcarbondioxideintheairresultingfromtheburningoffossilfuels(coalandoil)iscreatinga“greenhouseeffect”—holdinginheatreflectedfromtheearthandraisingtheworld'saveragetemperature.Ifthisviewiscorrectandtheworld'stemperatureisraisedonlyafewdegrees,muchofthepolaricecapwillmeltandcitiessuchasNewYork,Boston,Miami,andNewOrleanswillbeunderwater.Anotherview,lesswidelyheld,isthatincreasingparticulatematterintheatmosphereisblockingsunlightandloweringtheearth'stemperature—aresultthatwouldbeequallydisastrous.Adropofjustafewdegreescouldcreatesomethingclosetonewiceageandwouldmakeagriculturedifficultorimpossibleinmanyofourtopfarmingareas.Atpresentwedonotknowforsurethateitheroftheseconditionswillhappen(thoughonerecentgovernmentreportpreparedbyexpertsinthefieldconcludedthatthegreenhouseeffectisverylikely).Perhaps,ifweareverylucky,thetwotendencieswilloffseteachotherandtheworld'stemperaturewillstayaboutthesameasitisnow.
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