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1、LetmeshowyousomeofthemPopulationGrowth（人口增长）Increasinglylargenumbersofpeoplearebeingaddedtotheworldeveryyear.Asthenumberofpeopleincreases,morepollutionisgenerated,morehabitatsaredestroyed,andmorenaturalresourcesareusedup.Evenifnewtechnologicaladvanceswereabletocutinhalftheenvironmentalimpactthateac
2、hpersonhad,assoonastheworld'spopulationsizedoubled,theearthwouldbenobetteroffthanbefore.ThePopulationDivisionoftheUnitedNationspredictsthatthe5.63billionhumansalivein1994willincreaseto6.23billionintheyear2000,8.47billionin2025,and10.02billionin2050.Infact,becauselargeramountsofresourcesperpersonare
3、usedinthedevelopednations,eachcitizenfromthedevelopedworldhasamuchgreaterenvironmentalimpactthandoesacitizenfromadevelopingcountry.GlobalWarming（全球变暖）Thisprocessisreferredtoasthegreenhouseeffect.Thesegreenhousegases,primarilycarbondioxide,methane,nitrousoxide,insulatetheearth'ssurface,helpingtomain
4、tainwarmtemperatures.Iftheconcentrationofthesegaseswerehigher,moreheatwouldbetrappedwithintheatmosphere,andworldwidetemperatureswouldrise.Airpollution（空气污染）Asignificantportionofindustryandtransportationisbasedontheburningoffossilfuels,suchasgasoline.Asthesefuelsareburned,chemicalsandparticulatematt
5、erarereleasedintotheatmosphere.Thesechemicalsinteractwithoneanotherandwithultravioletradiationinsunlightinvariousdangerousways.Smog,usuallyfoundinurbanareaswithlargenumbersofautomobiles,cancauseserioushealthproblems.Waterpollution（水污染）Estimatessuggestthatnearly1.5billionpeoplelacksafedrinkingwatera
6、ndthatatleast5milliondeathsperyearcanbeattributedtowaterbornediseases.Pointsourcesdischargepollutantsatspecificlocations-from,forexample,factories,sewagetreatmentplants,oroiltankers.Nonpointsources-forexample,runoffwatercontainingpesticidesandfertilizersfromacresofagriculturalland-aremuchmorediffic
7、ulttocontrol.Pollutionarisingfromnonpointsourcesaccountsforamajorityofthecontaminantsinstreamsandlakes.SpeciesExtinction（物种灭绝）Whatisclearisthatspeciesaredyingoutatanunprecedentedrate;minimumestimatesareatle
