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.