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1、GlobalClimateChangeImpactsintheUnitedStatesGlobalClimateChangeGlobalClimateChangeKeyMessages:•Humanactivitieshaveledtolargeincreasesinheat-trappinggasesoverthepastcentury.•Globalaveragetemperatureandsealevelhaveincreased,andprecipitationpatternshavechanged.•Th
2、eglobalwarmingofthepast50yearsisdueprimarilytohuman-inducedincreasesinheat-trappinggases.Human“fingerprints”alsohavebeenidentifiedinmanyotheraspectsoftheclimatesystem,includingchangesinoceanheatcontent,precipitation,atmosphericmoisture,andArcticseaice.NATIONAL
3、LEVELCLIMATEIMPACTS•Globaltemperaturesareprojectedtocontinuetoriseoverthiscentury;byhowmuchandforhowlongdependsonanumberoffactors,includingtheamountofheat-trappinggasemissionsandhowsensitivetheclimateistothoseemissions.KeySourcesThisintroductiontoglobalclimate
4、changeexplainsverybrieflywhathas800,000YearRecordofCarbonDioxideConcentrationbeenhappeningtotheworld’sclimateandwhy,andwhatisprojectedtohappeninthefuture.WhilethisreportfocusesonclimatechangeimpactsintheUnitedStates,understandingthesechangesandtheirimpactsrequ
5、iresanunderstandingoftheglobalclimatesystem.Manychangeshavebeenobservedinglobalclimateoverthepastcentury.Thenatureandcausesofthesechangeshavebeencomprehensivelychronicledinavarietyofrecentreports,suchasthosebytheIntergovernmentalPanelLüthietal.;Tans;IIASA2onCl
6、imateChange(IPCC)andtheU.S.ClimateChangeScienceProgramAnalysisofairbubblestrappedinanAntarcticicecoreextendingback800,000yearsdocumentstheEarth’schangingcarbondioxideconcentration.Overthislongperiod,(CCSP).Thissectiondoesnotintendtonaturalfactorshavecausedthea
7、tmosphericcarbondioxideconcentrationtovaryduplicatethesecomprehensiveefforts,withinarangeofabout170to300partspermillion(ppm).Temperature-relateddatabutrathertoprovideabriefsynthesis,makeclearthatthesevariationshaveplayedacentralroleindeterminingtheglobalandtoi
8、ntegratemorerecentworkwithclimate.Asaresultofhumanactivities,thepresentcarbondioxideconcentrationofabout385ppmisabout30percentaboveitshighestleveloveratleastthelast800,000theassess
