2021年英语四级作文预测：空气污染思维导图

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.