Therewasonethoughtthatairpollutionaffectedonlytheareaimmediatelyaroundlargecitieswithfactoriesandheavyautomobiletraffic.Atpresentwerealizethatalthoughthesearetheareaswiththeworstairpollutiontheproblemisliterallyworldwide.OnseveraloccasionsoverthepastdecadeaheavycloudofairpollutionhascoveredtheeastoftheUnitedStatesandbroughthealthwarningsinruralareasawayfromanymajorconcentrationofmanufacturingandautomobiletraffic.Infacttheveryclimateoftheentireearthmaybeinfectedbyairpollution.Somescientistsconsiderthattheincreasingconcentrationofcarbondioxideintheairresultingfromtheburningoffossilfuels(coalandoil)iscreatinga“greenhouseeffect”—conservingheatreflectedfromtheearthandraisingtheworld’saveragetemperature.Ifthisviewiscorrectandtheworld’stemperatureisraisedonlyafewdegreesmuchofthepolaricecapwillmeltandcitiessuchasNewYorkBostonMiamiandNewOrleanswillbeinwater.
Anotherviewlesswidelyheldisthatincreasingparticularmatterintheatmosphereisblockingsunlightandloweringtheearth’stemperature—aresultthatwouldbeequallydisastrous.Adropofjustafewdegreescouldcreatesomethingclosetoanewiceageandwouldmakeagriculturedifficultorimpossibleinmanyofourtopfarmingareas.Todaywedonotknowforsurethateitheroftheseconditionswillhappen(thoughonerecentgovernmentreportdraftedbyexpertsinthefieldconcludedthatthegreenhouseeffectisverypossible).Perhapsifweareluckyenoughthetwotendencieswilloffseteachotherandtheworld’stemperaturewillstayaboutthesameasitisnow.Drivenbyeconomicprofitspeopleneglectthedamageonourenvironmentcausedbythe“advancedcivilization”.Maybetheairpollutionisthepricethehumanbeingshavetopayfortheirdevelopment.Butisitreallyworthwhile?
小题1:Aspointedoutatthebeginningofthepassagepeopleusedtothinkthatairpollution_______.