global warming | Definition, Causes, Effects, Solutions, & Facts

Global warming, the phenomenon of rising average air temperatures near Earth's surface over the past 100 to 200 years. Earth's climate has changed over ... globalwarming Sections&Media Article IntroductionClimaticvariationsincethelastglaciationCausesofglobalwarmingThegreenhouseeffectRadiativeforcingTheinfluencesofhumanactivityonclimateGreenhousegasesWatervapourCarbondioxideMethaneSurface-levelozoneandothercompoundsNitrousoxidesandfluorinatedgasesAerosolsLand-usechangeStratosphericozonedepletionNaturalinfluencesonclimateVolcanicaerosolsVariationsinsolaroutputVariationsinEarth’sorbitFeedbackmechanismsandclimatesensitivityWatervapourfeedbackCloudfeedbacksIcealbedofeedbackCarboncyclefeedbacksClimateresearchModernobservationsPrehistoricalclimaterecordsTheoreticalclimatemodelsPotentialeffectsofglobalwarmingSimulationsoffutureclimatechangePatternsofwarmingPrecipitationpatternsRegionalpredictionsIcemeltandsealevelriseOceancirculationchangesTropicalcyclonesEnvironmentalconsequencesofglobalwarmingSocioeconomicconsequencesofglobalwarmingGlobalwarmingandpublicpolicyTheIPCCandthescientificconsensusTheUNFrameworkConventionandtheKyotoProtocolFutureclimate-changepolicy FastFacts 2-MinSummary Facts&RelatedContent Media Videos Images AdditionalInfo AdditionalReading MoreArticlesOnThisTopic Contributors ArticleHistory Home Science EarthScience,GeologicTime&Fossils EarthSciences globalwarming Earthscience Print print Print Pleaseselectwhichsectionsyouwouldliketoprint: TableOfContents Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. 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TopQuestionsHowdoesglobalwarmingwork?HumanactivityaffectsglobalsurfacetemperaturesbychangingEarth’sradiativebalance—the“giveandtake”betweenwhatcomesinduringthedayandwhatEarthemitsatnight.Increasesingreenhousegases—i.e.,tracegasessuchascarbondioxideandmethanethatabsorbheatenergyemittedfromEarth’ssurfaceandreradiateitback—generatedbyindustryandtransportationcausetheatmospheretoretainmoreheat,whichincreasestemperaturesandaltersprecipitationpatterns.Wheredoesglobalwarmingoccurintheatmosphere?Globalwarming,thephenomenonofincreasingaverageairtemperaturesnearEarth’ssurfaceoverthepastonetotwocenturies,happensmostlyinthetroposphere,thelowestleveloftheatmosphere,whichextendsfromEarth’ssurfaceuptoaheightof6–11miles.ThislayercontainsmostofEarth’scloudsandiswherelivingthingsandtheirhabitatsandweatherprimarilyoccur.Whyisglobalwarmingasocialproblem?Continuedglobalwarmingisexpectedtoimpacteverythingfromenergyusetowateravailabilitytocropproductivitythroughouttheworld.Poorcountriesandcommunitieswithlimitedabilitiestoadapttothesechangesareexpectedtosufferdisproportionately.Globalwarmingisalreadybeingassociatedwithincreasesintheincidenceofsevereandextremeweather,heavyflooding,andwildfires—phenomenathatthreatenhomes,dams,transportationnetworks,andotherfacetsofhumaninfrastructure.LearnmoreabouthowtheIPCC’sSixthAssessmentReport,releasedin2021,describesthesocialimpactsofglobalwarming.Wheredoesglobalwarmingaffectpolarbears?PolarbearsliveintheArctic,wheretheyusetheregion’sicefloesastheyhuntsealsandothermarinemammals.Temperatureincreasesrelatedtoglobalwarminghavebeenthemostpronouncedatthepoles,wheretheyoftenmakethedifferencebetweenfrozenandmeltedice.Polarbearsrelyonsmallgapsintheicetohunttheirprey. Asthesegapswidenbecauseofcontinuedmelting,preycapturehasbecomemorechallengingfortheseanimals.StudytheeffectofincreasingconcentrationsofcarbondioxideonEarth'satmosphereandplantlifeAnoverviewoftherolegreenhousegasesplayinmodifyingEarth'sclimate.EncyclopædiaBritannica,Inc.Seeallvideosforthisarticleglobalwarming,thephenomenonofincreasingaverageairtemperaturesnearthesurfaceofEarthoverthepastonetotwocenturies.Climatescientistshavesincethemid-20thcenturygathereddetailedobservationsofvariousweatherphenomena(suchastemperatures,precipitation,andstorms)andofrelatedinfluencesonclimate(suchasoceancurrentsandtheatmosphere’schemicalcomposition).ThesedataindicatethatEarth’sclimatehaschangedoveralmosteveryconceivabletimescalesincethebeginningofgeologictimeandthattheinfluenceofhumanactivitiessinceatleastthebeginningoftheIndustrialRevolutionhasbeendeeplywovenintotheveryfabricofclimatechange.Givingvoicetoagrowingconvictionofmostofthescientificcommunity,theIntergovernmentalPanelonClimateChange(IPCC)wasformedin1988bytheWorldMeteorologicalOrganization(WMO)andtheUnitedNationsEnvironmentProgram(UNEP).In2013theIPCCreportedthattheintervalbetween1880and2012sawanincreaseinglobalaveragesurfacetemperatureofapproximately0.9°C(1.5°F).Theincreaseiscloserto1.1°C(2.0°F)whenmeasuredrelativetothepreindustrial(i.e.,1750–1800)meantemperature.globalwarmingscenariosGraphofthepredictedincreaseinEarth'saveragesurfacetemperatureaccordingtoaseriesofclimatechangescenariosthatassumedifferentlevelsofeconomicdevelopment,populationgrowth,andfossilfueluse.Theassumptionsmadebyeachscenarioaregivenatthebottomofthegraph.EncyclopædiaBritannica,Inc.AspecialreportproducedbytheIPCCin2018honedthisestimatefurther,notingthathumanbeingsandhumanactivitieshavebeenresponsibleforaworldwideaveragetemperatureincreaseofbetween0.8and1.2°C(1.4and2.2°F)ofglobalwarmingsincepreindustrialtimes,andmostofthewarmingobservedoverthesecondhalfofthe20thcenturycouldbeattributedtohumanactivities.Itpredictedthattheglobalmeansurfacetemperaturewouldincreasebetween3and4°C(5.4and7.2°F)by2100relativetothe1986–2005averageshouldcarbonemissionscontinueattheircurrentrate.Thepredictedriseintemperaturewasbasedonarangeofpossiblescenariosthataccountedforfuturegreenhousegasemissionsandmitigation(severityreduction)measuresandonuncertaintiesinthemodelprojections.Someofthemainuncertaintiesincludethepreciseroleoffeedbackprocessesandtheimpactsofindustrialpollutantsknownasaerosols,whichmayoffsetsomewarming.Manyclimatescientistsagreethatsignificantsocietal,economic,andecologicaldamagewouldresultifglobalaveragetemperaturesrosebymorethan2°C(3.6°F)insuchashorttime.Suchdamagewouldincludeincreasedextinctionofmanyplantandanimalspecies,shiftsinpatternsofagriculture,andrisingsealevels.By2015allbutafewnationalgovernmentshadbeguntheprocessofinstitutingcarbonreductionplansaspartoftheParisAgreement,atreatydesignedtohelpcountrieskeepglobalwarmingto1.5°C(2.7°F)abovepreindustriallevelsinordertoavoidtheworstofthepredictedeffects.AuthorsofaspecialreportpublishedbytheIPCCin2018notedthatshouldcarbonemissionscontinueattheirpresentrate,theincreaseinaveragenear-surfaceairtemperatureswouldreach1.5°Csometimebetween2030and2052.PastIPCCassessmentsreportedthattheglobalaveragesealevelrosebysome19–21cm(7.5–8.3inches)between1901and2010andthatsealevelsrosefasterinthesecondhalfofthe20thcenturythaninthefirsthalf.Italsopredicted,againdependingonawiderangeofscenarios,thattheglobalaveragesealevelwouldrise26–77cm(10.2–30.3inches)relativetothe1986–2005averageby2100forglobalwarmingof1.5°C,anaverageof10cm(3.9inches)lessthanwhatwouldbeexpectedifwarmingroseto2°C(3.6°F)abovepreindustriallevels. 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SubscribeNow Thescenariosreferredtoabovedependmainlyonfutureconcentrationsofcertaintracegases,calledgreenhousegases,thathavebeeninjectedintotheloweratmosphereinincreasingamountsthroughtheburningoffossilfuelsforindustry,transportation,andresidentialuses.Modernglobalwarmingistheresultofanincreaseinmagnitudeoftheso-calledgreenhouseeffect,awarmingofEarth’ssurfaceandloweratmospherecausedbythepresenceofwatervapour,carbondioxide,methane,nitrousoxides,andothergreenhousegases.In2014theIPCCreportedthatconcentrationsofcarbondioxide,methane,andnitrousoxidesintheatmospheresurpassedthosefoundinicecoresdatingback800,000years.greenhouseeffectonEarthThegreenhouseeffectonEarth.SomeincomingsunlightisreflectedbyEarth'satmosphereandsurface,butmostisabsorbedbythesurface,whichiswarmed.Infrared(IR)radiationisthenemittedfromthesurface.SomeIRradiationescapestospace,butsomeisabsorbedbytheatmosphere'sgreenhousegases(especiallywatervapour,carbondioxide,andmethane)andreradiatedinalldirections,sometospaceandsomebacktowardthesurface,whereitfurtherwarmsthesurfaceandtheloweratmosphere.EncyclopædiaBritannica,Inc.Ofallthesegases,carbondioxideisthemostimportant,bothforitsroleinthegreenhouseeffectandforitsroleinthehumaneconomy.Ithasbeenestimatedthat,atthebeginningoftheindustrialageinthemid-18thcentury,carbondioxideconcentrationsintheatmospherewereroughly280partspermillion(ppm).Bythemiddleof2018theyhadrisento406ppm,and,iffossilfuelscontinuetobeburnedatcurrentrates,theyareprojectedtoreach550ppmbythemid-21stcentury—essentially,adoublingofcarbondioxideconcentrationsin300years.Avigorousdebateisinprogressovertheextentandseriousnessofrisingsurfacetemperatures,theeffectsofpastandfuturewarmingonhumanlife,andtheneedforactiontoreducefuturewarminganddealwithitsconsequences.Thisarticleprovidesanoverviewofthescientificbackgroundandpublicpolicydebaterelatedtothesubjectofglobalwarming.Itconsidersthecausesofrisingnear-surfaceairtemperatures,theinfluencingfactors,theprocessofclimateresearchandforecasting,thepossibleecologicalandsocialimpactsofrisingtemperatures,andthepublicpolicydevelopmentssincethemid-20thcentury.ForadetaileddescriptionofEarth’sclimate,itsprocesses,andtheresponsesoflivingthingstoitschangingnature,seeclimate.ForadditionalbackgroundonhowEarth’sclimatehaschangedthroughoutgeologictime,seeclimaticvariationandchange.ForafulldescriptionofEarth’sgaseousenvelope,withinwhichclimatechangeandglobalwarmingoccur,seeatmosphere. 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