Causes of climate change - Canada.ca

Carbon dioxide is the main cause of human-induced climate change. It has been emitted in vast quantities from the burning of fossil fuels and it ... Skiptomaincontent Skipto"Aboutgovernment" Causesofclimatechange Whatisthemostimportantcauseofclimatechange? Humanactivityisthemaincauseofclimatechange.Peopleburnfossilfuelsandconvertlandfromforeststoagriculture.SincethebeginningoftheIndustrialRevolution,peoplehaveburnedmoreandmorefossilfuelsandchangedvastareasoflandfromforeststofarmland. Burningfossilfuelsproducescarbondioxide,agreenhousegas.Itiscalledagreenhousegasbecauseitproducesa“greenhouseeffect”.Thegreenhouseeffectmakestheearthwarmer,justasagreenhouseiswarmerthanitssurroundings. Carbondioxideisthemaincauseofhuman-inducedclimatechange. Itstaysintheatmosphereforaverylongtime.Othergreenhousegases,suchasnitrousoxide,stayintheatmosphereforalongtime.Othersubstancesonlyproduceshort-termeffects. Notallsubstancesproducewarming.Some,likecertainaerosols,canproducecooling. Whatareclimateforcers? Carbondioxideandothersubstancesarereferredtoasclimateforcersbecausetheyforceorpushtheclimatetowardsbeingwarmerorcooler.Theydothisbyaffectingtheflowofenergycomingintoandleavingtheearth’sclimatesystem. Smallchangesinthesun’senergythatreachestheearthcancausesomeclimatechange.ButsincetheIndustrialRevolution,addinggreenhousegaseshasbeenover50timesmorepowerfulthanchangesintheSun'sradiance.Theadditionalgreenhousegasesinearth’satmospherehavehadastrongwarmingeffectonearth’sclimate. Futureemissionsofgreenhousegases,particularlycarbondioxide,willdeterminehowmuchmoreclimatewarmingoccurs. Whatcanbedoneaboutclimatechange? Carbondioxideisthemaincauseofhuman-inducedglobalwarmingandassociatedclimatechange.Itisaverylong-livedgas,whichmeanscarbondioxidebuildsupintheatmospherewithongoinghumanemissionsandremainsintheatmosphereforcenturies.Globalwarmingcanonlybestoppedbyreducingglobalemissionsofcarbondioxidefromhumanfossilfuelcombustionandindustrialprocessestozero,butevenwithzeroemissions,theglobaltemperaturewillremainessentiallyconstantatitsnewwarmerlevel.Emissionsofothersubstancesthatwarmtheclimatemustalsobesubstantiallyreduced.Thisindicateshowdifficultthechallengeis. Whatisclimatechange? Climatechangeisalong-termshiftinweatherconditionsidentifiedbychangesintemperature,precipitation,winds,andotherindicators.Climatechangecaninvolvebothchangesinaverageconditionsandchangesinvariability,including,forexample,extremeevents. Theearth'sclimateisnaturallyvariableonalltimescales.However,itslong-termstateandaveragetemperatureareregulatedbythebalancebetweenincomingandoutgoingenergy,whichdeterminestheEarth'senergybalance.Anyfactorthatcausesasustainedchangetotheamountofincomingenergyortheamountofoutgoingenergycanleadtoclimatechange.Differentfactorsoperateondifferenttimescales,andnotallofthosefactorsthathavebeenresponsibleforchangesinearth'sclimateinthedistantpastarerelevanttocontemporaryclimatechange.Factorsthatcauseclimatechangecanbedividedintotwocategories­-thoserelatedtonaturalprocessesandthoserelatedtohumanactivity.Inadditiontonaturalcausesofclimatechange,changesinternaltotheclimatesystem,suchasvariations. Inoceancurrentsoratmosphericcirculation,canalsoinfluencetheclimateforshortperiodsoftime.Thisnaturalinternalclimatevariabilityissuperimposedonthelong-termforcedclimatechange. Doesclimatechangehavenaturalcauses? TheEarth'sclimatecanbeaffectedbynaturalfactorsthatareexternaltotheclimatesystem,suchaschangesinvolcanicactivity,solaroutput,andtheEarth'sorbitaroundtheSun.Ofthese,thetwofactorsrelevantontimescalesofcontemporaryclimatechangearechangesinvolcanicactivityandchangesinsolarradiation.IntermsoftheEarth'senergybalance,thesefactorsprimarilyinfluencetheamountofincomingenergy.Volcaniceruptionsareepisodicandhaverelativelyshort-termeffectsonclimate.ChangesinsolarirradiancehavecontributedtoclimatetrendsoverthepastcenturybutsincetheIndustrialRevolution,theeffectofadditionsofgreenhousegasestotheatmospherehasbeenover50timesthatofchangesintheSun'soutput. Humancauses Climatechangecanalsobecausedbyhumanactivities,suchastheburningoffossilfuelsandtheconversionoflandforforestryandagriculture.SincethebeginningoftheIndustrialRevolution,thesehumaninfluencesontheclimatesystemhaveincreasedsubstantially.Inadditiontootherenvironmentalimpacts,theseactivitieschangethelandsurfaceandemitvarioussubstancestotheatmosphere.Theseinturncaninfluenceboththeamountofincomingenergyandtheamountofoutgoingenergyandcanhavebothwarmingandcoolingeffectsontheclimate. Thedominantproductoffossilfuelcombustioniscarbondioxide,agreenhousegas.TheoveralleffectofhumanactivitiessincetheIndustrialRevolutionhasbeenawarmingeffect,drivenprimarilybyemissionsofcarbondioxideandenhancedbyemissionsofothergreenhousegases. Thebuild-upofgreenhousegasesintheatmospherehasledtoanenhancementofthenaturalgreenhouseeffect. Itisthishuman-inducedenhancementofthegreenhouseeffectthatisofconcernbecauseongoingemissionsofgreenhousegaseshavethepotentialtowarmtheplanettolevelsthathaveneverbeenexperiencedinthehistoryofhumancivilization.Suchclimatechangecouldhavefar-reachingand/orunpredictableenvironmental,social,andeconomicconsequences. Short-livedandlong-livedclimateforcers Carbondioxideisthemaincauseofhuman-inducedclimatechange.Ithasbeenemittedinvastquantitiesfromtheburningoffossilfuelsanditisaverylong-livedgas,whichmeansitcontinuestoaffecttheclimatesystemduringitslongresidencetimeintheatmosphere.However,fossilfuelcombustion,industrialprocesses,agriculture,andforestry-relatedactivitiesemitothersubstancesthatalsoactasclimateforcers.Some,suchasnitrousoxide,arelong-livedgreenhousegaseslikecarbondioxide,andsocontributetolong-termclimatechange.Othersubstanceshaveshorteratmosphericlifetimesbecausetheyareremovedfairlyquicklyfromtheatmosphere.Therefore,theireffectontheclimatesystemissimilarlyshort-lived.Together,theseshort-livedclimateforcersareresponsibleforasignificantamountofcurrentclimateforcingfromanthropogenicsubstances.Someshort-livedclimateforcershaveaclimatewarmingeffect(‘positiveclimateforcers')whileothershaveacoolingeffect(‘negativeclimateforcers'). Ifatmosphericlevelsofshort-livedclimateforcersarecontinuallyreplenishedbyongoingemissions,thesecontinuetoexertaclimateforcing.However,reducingemissionswillquitequicklyleadtoreducedatmosphericlevelsofsuchsubstances.Anumberofshort-livedclimateforcershaveclimatewarmingeffectsandtogetherarethemostimportantcontributorstothehumanenhancementofthegreenhouseeffectaftercarbondioxide.Thisincludesmethaneandtroposphericozone–bothgreenhousegases–andblackcarbon,asmallsolidparticleformedfromtheincompletecombustionofcarbon-basedfuels(coal,oilandwoodforexample). Othershort-livedclimateforcershaveclimatecoolingeffects,mostnotablysulphateaerosols.Fossilfuelcombustionemitssulphurdioxideintotheatmosphere(inadditiontocarbondioxide)whichthencombineswithwatervapourtoformtinydroplets(aerosols)whichreflectsunlight.Sulphateaerosolsremainintheatmosphereforonlyafewdays(washingoutinwhatisreferredtoasacidrain),andsodonothavethesamelong-termeffectasgreenhousegases.Thecoolingfromsulphateaerosolsintheatmospherehas,however,offsetsomeofthewarmingfromothersubstances.Thatis,thewarmingwehaveexperiencedtodatewouldhavebeenevenlargerhaditnotbeenforelevatedlevelsofsulphateaerosolsintheatmosphere. LearnmoreabouttheEarth'sclimatesystem. 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