Effects of global warmingWord文件下载.docx
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Effects of global warmingWord文件下载.docx
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threatstoendangeredspeciesanduniquesystems,damagesfromextremeclimateevents,effectsthatfallmostheavilyondevelopingcountriesandthepoorwithincountries,globalaggregateimpacts(i.e.,variousmeasurementsoftotalsocial,economicandecologicalimpacts),[3][4]andlarge-scalehigh-impactevents.Theabove"
burningembers"
diagramwasproducedbytheIPCCin2001.Alaterrevisionofthediagram,publishedin2009,butnotapprovedbytheIPCC,showsincreasedrisks.[5]
Thisarticleisabouttheeffectsofglobalwarmingandclimatechange.Theeffects,orimpacts,ofclimatechangemaybephysical,ecological,socialoreconomic.Evidenceofobservedclimatechangeincludestheinstrumentaltemperaturerecord,risingsealevels,anddecreasedsnowcoverintheNorthernHemisphere.[6]AccordingtotheIntergovernmentalPanelonClimateChange(IPCC,2007a:
10),"
[most]oftheobservedincreaseinglobalaveragetemperaturessincethemid-20thcenturyisverylikelyduetotheobservedincreasein[humangreenhousegas]concentrations"
.Itispredictedthatfutureclimatechangeswillincludefurtherglobalwarming(i.e.,anupwardtrendinglobalmeantemperature),sealevelrise,andaprobableincreaseinthefrequencyofsomeextremeweatherevents.SignatoriesoftheUnitedNationsFrameworkConventiononClimateChangehaveagreedtoimplementpoliciesdesignedtoreducetheiremissionsofgreenhousegases.
Definitions
Inthisarticle,thephrase“climatechange”isusedtodescribeachangeintheclimate,measuredintermsofitsstatisticalproperties,e.g.,theglobalmeansurfacetemperature.[7]Inthiscontext,“climate”istakentomeantheaverageweather.Climatecanchangeoverperiodoftimerangingfrommonthstothousandsormillionsofyears.Theclassicaltimeperiodis30years,asdefinedbytheWorldMeteorologicalOrganization.Theclimatechangereferredtomaybeduetonaturalcauses,e.g.,changesinthesun'
soutput,orduetohumanactivities,e.g.,changingthecompositionoftheatmosphere.[8]Anyhuman-inducedchangesinclimatewilloccuragainstthe“background”ofnaturalclimaticvariations(seeattributionofrecentclimatechangeformoreinformation).
Inthisarticle,thephrase“globalwarming”referstothechangeintheEarth'
sglobalaveragesurfacetemperature.[9]Measurementsshowaglobaltemperatureincreaseof1.4
°
F(0.78
C)betweentheyears1900and2005.Globalwarmingiscloselyassociatedwithabroadspectrumofotherclimatechanges,suchasincreasesinthefrequencyofintenserainfall,decreasesinsnowcoverandseaice,morefrequentandintenseheatwaves,risingsealevels,andwidespreadoceanacidification.[10]
Temperaturechanges
Globalmeansurfacetemperaturedifferencefromtheaveragefor1880–2009
Thisarticlebreaksdownsomeoftheimpactsofclimatechangeaccordingtodifferentlevelsoffutureglobalwarming.Thiswayofdescribingimpactshas,forinstance,beenusedintheIPCC'
sAssessmentReportsonclimatechange.[11]Theinstrumentaltemperaturerecordshowsglobalwarmingofaround0.6°
Covertheentire20thcentury.[12]Thefuturelevelofglobalwarmingisuncertain,butawiderangeofestimates(projections)havebeenmade.[13]TheIPCC'
s"
SRES"
scenarioshavebeenfrequentlyusedtomakeprojectionsoffutureclimatechange.[14]:
22-24ClimatemodelsusingthesixSRES"
marker"
scenariossuggestfuturewarmingof1.1to6.4°
Cbytheendofthe21stcentury(aboveaverageglobaltemperaturesoverthe1980to1999timeperiod).[15]Therangeintemperatureprojectionspartlyreflectsdifferentprojectionsoffuturesocialandeconomicdevelopment(e.g.,economicgrowth,populationlevel,energypolicies),whichinturnaffectsprojectionsofgreenhousegas(GHG)emissions.TherangealsoreflectsuncertaintyintheresponseoftheclimatesystemtopastandfutureGHGemissions(measuredbytheclimatesensitivity).
Theprojectedrateofwarmingunderthesescenarioswouldverylikelybewithoutprecedentduringatleastthelast10,000years(seefootnote1).[16]Themostrecentwarmperiodcomparabletotheseprojectionswasthemid-Pliocene,around3millionyearsago.[17]Atthattime,modelssuggestthatmeanglobaltemperatureswereabout2–3°
Cwarmerthanpre-industrialtemperatures.[18]
Physicalimpacts
Mainarticle:
Physicalimpactsofclimatechange
Keyclimateindicatorsthatshowglobalwarming.[19]:
2-3
WorkingGroupI'
scontributiontotheIPCCFourthAssessmentReport,publishedin2007,concludedthatwarmingoftheclimatesystemwas"
unequivocal."
[20]Thiswasbasedontheconsistencyofevidenceacrossarangeofobservedchanges,includingincreasesinglobalaverageairandoceantemperatures,widespreadmeltingofsnowandice,andrisingglobalaveragesealevel.[21]
Humanactivitieshavecontributedtoanumberoftheobservedchangesinclimate.[22]Thiscontributionhasprincipallybeenthroughtheburningoffossilfuels,whichhasledtoanincreaseintheconcentrationofGHGsintheatmosphere.[23]Anotherhumaninfluenceontheclimatearesulfurdioxideemissions,whichareaprecursortotheformationofsulfateaerosolsintheatmosphere.[24]
Human-inducedwarmingcouldpotentiallyleadtosomeimpactsthatareabruptorirreversible(seethesectiononAbruptorirreversiblechanges).[15][25]Theprobabilityofwarminghavingunforeseenconsequencesincreaseswiththerate,magnitude,anddurationofclimatechange.[26]
Radiativeforcing
Theeffectofhumanactivitiesontheclimatesystemcanbemeasuredbyradiativeforcing:
EnergyisconstantlyflowingintotheatmosphereintheformofsunlightthatalwaysshinesonhalfoftheEarth'
ssurface.[27]Someofthissunlightisreflectedbacktospaceandtherestisabsorbedbytheplanet.SomeenergyfromtheEarthisalsoradiatedbackoutintospaceasinvisibleinfraredlight.RadiativeforcingisameasureoftheenergyflowingintotheEarth-atmospheresystem,minustheenergyflowingout.Apositiveradiativeforcingwilltendtowarmtheclimate,whileanegativeforcingwilltendtocooltheclimate.[28]Anthopogenicforcing(i.e.,theradiativeforcingduetohumanactivites)wasestimatedtohavebeenpositiveintheyear2005.[28]Thisisrelativetotheestimatedforcingsatthestartoftheindustrialera,takenastheyear1750.Anthropogenicforcingoftheclimatehaslikelytocontributedtoanumberofobservedchanges,includingsealevelrise,changesinclimateextremes(suchaswarmandcolddays),declinesinArcticseaiceextent,andtoglacierretreat.[22]
Effectsonweather
Observationsshowthattherehavebeenchangesinweather.[29]Asclimatechanges,theprobabilitiesofcertaintypesofweathereventsareaffected.
Changeshavebeenobservedintheamount,intensity,frequency,andtypeofprecipitation.[14]:
18Widespreadincreasesinheavyprecipitationhaveoccurred,eveninplaceswheretotalrainamountshavedecreased.IPCC(2007d)concludedthathumaninfluenceshad,morelikelythannot(greaterthan50%probability,basedonexpertjudgement),[30]ledtoanincreaseinthefrequencyofheavyprecipitationevents.[31]Projectionsoffuturechangesinprecipitationshowoverallincreasesintheglobalaverage,butwithsubstantialshiftsinwhereandhowprecipitationfalls.[14]:
24Climatemodelstendtoprojectincreasingprecipitationathighlatitudesandinthetropics(e.g.,thesouth-eastmonsoonregionandoverthetropicalPacific)anddecreasingprecipitationinthesub-tropics(e.g.,overmuchofNorthAfricaandthenorthernSahara).[32]
Evidencesuggeststhat,sincethe1970s,therehavebeensubstantialincreasesintheintensityanddurationoftropicalstormsandhurricanes.[33]Modelsprojectageneraltendencyformoreintensebutfewerstormsoutsidethetropics.[14]:
24
AccumulatedcycloneenergyintheAtlanticOceanandtheseasurfacetemperaturedifferencewhichinfluencessuch,measuredbytheU.S.NOAA.
Extremeweather
Seealso:
Extremeweather,Tropicalcyclone#Globalwarming,
andListofAtlantichurricanerecords
Sincethelate20thcentury,changeshavebeenobservedinthetrendsofsomeextremeweatherandclimateevents,e.g.,heatwaves.[34]Humanactivitieshave,withvaryingdegreesofconfidence,contributedtosomeoftheseobservedtrends.Projectionsforthe21stcenturysuggestcontinuingchangesintrendsforsomeextremeevents.Solomonetal.(2007),forexample,projectedthefollowinglikely(greaterthan66%probability,basedonexpertjudgement)[30]changes:
[34]
▪anincreaseintheareasaffectedbydrought;
▪increasedtropicalcycloneactivity;
▪andincreasedincidenceofextremehighsealevel(excludingtsunamis).
Projectedchangesinextremeeventswillhavepredominantlyadverseimpactsonecosystemsandhumansociety.[35][36]
Glacierretreatanddisappearance
Retreatofglacierssince1850
Amapofthechangeinthicknessofmountainglacierssince1970.Thinninginorangeandred,thickeninginblue.
IPCC(2007a:
5)foundthat,onaverage,mountainglaciersandsnowcoverhaddecreasedinboththenorthernandsouthernhemispheres.[20]Thiswidespreaddecreaseinglaciersandicecapshadcontributedtoobservedsealevelrise.Withveryhighorhighconfidence(seefootnote2),IPCC(2007b[37
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