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1、2010届上海市高三英语二模汇编——C篇（奉贤）(C)AgainstthesuppositionthatforestfiresinAlaska,CanadaandSiberiawarmtheclimate,scientistshavediscoveredthatcoolingmayoccurinareaswhereburnttreesallowmoresnowtomirrormoresunlightintospace.Thisfindingsuggeststhattakingstepstopreventnorthernfor
2、esttolimitthereleaseofgreenhousegasesmaywarmtheclimateinnorthernregions.Usuallylargefiresdestroyedforestsintheseareasoverthepastdecade.Scientistspredictthatwithclimatewarming,firesmayoccurmorefrequentlyovernextseveralcenturiesasaresultofalongerfireseason.Sunlightta
3、keninbytheearthtendstocausewarming,whileheatmirroredbackintospacetendstocausecooling.Thisisthefirststudytoanalyzeallaspectsofhownorthernfiresinfluenceclimate.Earlierstudiesbyotherscientistshavesuggestedthatfireinnorthernregionsspeedupclimatewarmingbecausegreenhouse
4、gasesfromburningtreesandplantsarereleasedintotheatmosphereandthustrapheat.Scientistsfoundthatlightafterthefire,largeamountsofgreenhousegasesenteredtheatmosphereandcausedwarming.Ozone(臭氧)levelsincreased,aidashfromthefirefellonfar-offseaice,darkeningthesurfaceandcaus
5、ingmoreradiationfromthesuntobetakenin.Thefollowingspring,however,thelandwithintheareaofthefirewasbrighterthanbeforethefire,becausefewertreescoveredtheground.Snowonthegroundmirroredmoresunlightbackintospace,leadingtocooling."Weneedtofindoutallpossiblewaystoreducethe
6、growthofgreenhousegasesintheatmosphere."Scientiststrackedthechangeinamountofradiationenteringandleavingtheclimatesystemasaresultofthefire,andfoundameasurementcloselyrelatedtotheglobalairtemperature.Typically,fireinnorthernregionsoccursinthesameareaevery80to150years
7、.Scientists,however,foundthatwhenfireoccursmorefrequently,moreradiationislostfromtheearthandcoolingresults.Specifically,theydeterminedwhenfirereturns20yearsearlierthanpredicated,0.5wattspersquaremeterofareaburnedaresoakedupbytheearthfromgreenhousegases,but0.9wattsp
8、ersquaremeterwillbesentbackintospace.Theneteffectiscooling.Wattsareusedtomeasuretherateatwhichenergyisgainedorlostfromtheearth.72.Accordingtothen
