Effects of global warming.docx

Effects of global warming.docx

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Effectsofglobalwarming

Effectsofglobalwarming

FromWikipedia,thefreeencyclopedia

Thisarticleisabout（primarily）effectsduringthe21stcentury.Forlongertermeffects,seeLong-termeffectsofglobalwarming.

Thevariouseffectsofclimatechangeposerisksthatincreasewithglobalwarming（i.e.,increasesintheEarth'sglobalmeantemperature）.[1][2]TheIPCC（2001d[1]and2007d）[3]hasorganizedmanyoftheserisksintofive"reasonsforconcern:

"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

Mainarticle:

Retreatofglacierssince1850

Amapofthechangeinthicknessofmountainglacierssince1970.Thinninginorangeandred,thickeninginblue.

IPCC（2007a:

5）foundthat,onaverage,mountainglaciersandsnowcoverhaddecreasedinboththenorthernandsouthernhemispheres.[20]Thiswidespreaddecreaseinglaciersandicecapshadcontributedtoobservedsealevelrise.Withveryhighorhighconfidence（seefootnote2）,IPCC（2007b[37