Causes of climate change - Met Office

The evidence is clear: the main cause of climate change is burning fossil fuels such as oil, gas, and coal. When burnt, fossil fuels release carbon dioxide ... Causesofclimatechange Theevidenceisclear:themaincauseofclimatechangeisburningfossilfuelssuchasoil,gas,andcoal.Whenburnt,fossilfuelsreleasecarbondioxideintotheair,causingtheplanettoheatup. Whatcausesclimatechange? TheclimateonEarthhasbeenchangingsinceitformed4.5billionyearsago.Untilrecently,naturalfactorshavebeenthecauseofthesechanges.Naturalinfluencesontheclimateincludevolcaniceruptions,changesintheorbitoftheEarth,andshiftsintheEarth'scrust(knownasplatetectonics). Overthepastonemillionyears,theEarthhasexperiencedaseriesoficeages,includingcoolerperiods(glacials)andwarmerperiods(interglacials).Glacialandinterglacialperiodscycleroughlyevery100,000years,causedbychangesinEarth'sorbitaroundthesun.Forthepastfewthousandyears,Earthhasbeeninaninterglacialperiodwithaconstanttemperature. However,sincetheIndustrialRevolutioninthe1800s,theglobaltemperaturehasincreasedatamuchfasterrate.Byburningfossilfuelsandchanginghowweusetheland,humanactivityhasquicklybecometheleadingcauseofchangestoourclimate. Howdoestheclimatesystemwork? Greenhousegasesandthegreenhouseeffect SomegasesintheEarth'satmospheretrapheatandstopitescapingintospace.Wecallthese'greenhousegases'.Thesegases actasawarmingblanketaroundtheEarth,knownasthe'greenhouseeffect'. Greenhousegasescomefrombothhumanandnaturalsources.Gaseslikecarbondioxide,methane,andnitrousoxidenaturallyoccurintheatmosphere.Others,suchaschlorofluorocarbons(CFCs),areonlyproducedbyhumanactivity. Whenshort-wave radiationfromthesunreachesEarth,mostofitpassesstraightthroughandhitsthesurface.TheEarthabsorbsmostofthisradiationandgivesofflonger-wavelengthinfraredradiation. Thegreenhousegasesabsorbsomeofthisinfraredradiation,insteadofitpassingstraightoutintospace.Theatmospherethenemitsradiationinalldirections,sendingsomeofitbacktothesurface,causingtheplanettoheatup.Thisprocessisknownasthe'greenhouseeffect'. Thegreenhouseeffectiscriticaltooursurvival.Infact,withoutgreenhousegases,Earthwouldbeabout30degreescolderthanitistoday.Withoutgreenhousegasesandtheirwarmingeffect,wewouldn'tbeabletosurvive. However,sincetheIndustrialRevolution,we'vebeenaddingmoreandmoregreenhousegasesintotheair,trappingevenmoreheat.InsteadofkeepingEarthatawarm,stabletemperature,thegreenhouseeffectisheatingtheplanetatamuchfasterrate.Wecallthisthe'enhancedgreenhouseeffect' andit'sthemaincauseofclimatechange. Humancausesofclimatechange Humanscauseclimatechangebyreleasingcarbondioxideandothergreenhousegasesintotheair.Today,thereismorecarbondioxideintheatmospherethanthereeverhasbeen in atleast thepast2millionyears.Duringthe20thand21stcentury,thelevelofcarbondioxideroseby40%. Weproducegreenhousegasesinlotsofdifferentways: Burningfossilfuels–Fossilfuelssuchasoil,gas,andcoalcontaincarbondioxidethathasbeen'lockedaway'inthegroundforthousandsofyears.Whenwetaketheseoutofthelandandburnthem,wereleasethestoredcarbondioxideintotheair. Deforestation–Forestsremoveandstorecarbondioxidefromtheatmosphere.Cuttingthemdownmeansthatcarbondioxidebuildsupquickersincetherearenotreestoabsorbit.Notonlythat,treesreleasethecarbontheystoredwhenweburnthem. Agriculture–Plantingcropsandrearinganimalsreleasesmanydifferenttypesofgreenhousegasesintotheair.Forexample,animalsproducemethane,whichis30timesmorepowerfulthancarbondioxideasagreenhousegas.Thenitrousoxideusedforfertilisersistentimesworseandisnearly300timesmorepotentthancarbondioxide! Cement–Producingcementisanothercontributortoclimatechange,causing2%ofourentirecarbondioxideemissions. Naturalchangestotheclimate Theleadingcauseofclimatechangeishumanactivityandthereleaseofgreenhousegases.However,therearelotsofnaturalcausesthatalsoleadtochangesintheclimatesystem. Naturalcyclescancausetheclimatetoalternatebetweenwarmingandcooling.Therearealsonaturalfactorsthatforcetheclimatetochange,knownas'forcings'.Eventhoughthesenaturalcausescontributetoclimatechange,weknowthattheyarenottheprimarycause,basedonscientificevidence. Someofthesenaturalcyclesinclude: Milankovitchcycles–AsEarthtravelsaroundthesun,itspathandthetiltofitsaxiscanchangeslightly.Thesechanges,calledMilankovitchcycles,affecttheamountofsunlightthatfallsonEarth.ThiscancausethetemperatureofEarthtochange.However,thesecyclestakeplaceovertensorhundredsofthousandsofyearsandareunlikelytobecausingthechangestotheclimatethatweareseeingtoday. ElNiñoSouthernOscillation(ENSO)–ENSOisapatternofchangingwatertemperaturesinthePacificOcean.Inan'ElNiño'year,theglobaltemperaturewarmsup,andina'LaNiña'year,itcoolsdown.Thesepatternscanaffecttheglobaltemperatureforashortamountoftime(monthsoryears)butcannotexplainthepersistentwarmingthatweseetoday. WhatisElNiño,whatdoesitmeanandhowdoesitaffectweatheraroundtheworld? Naturalforcingsthatcancontributetoclimatechangeinclude: Solarirradiance–ChangingenergyfromthesunhasaffectedthetemperatureofEarthinthepast.However,wehavenotseenanythingstrongenoughtochangeourclimate.AnyincreaseinsolarenergywouldmaketheentireatmosphereofEarthwarm,butwecanonlyseewarminginthebottomlayer. Volcaniceruptions–Volcanoeshaveamixedeffectonourclimate.EruptionsproduceaerosolparticlesthatcoolEarth,buttheyalsoreleasecarbondioxide,whichwarmsit.Volcanoesproduce50timeslesscarbondioxidethanhumansdo,soweknowtheyarenottheleadingcauseofglobalwarming.Ontopofthis,coolingisthedominanteffectofvolcaniceruptions,notwarming. Arehumansresponsibleforclimatechange? Whenlookingatalltheevidence,thereisalargescientificconsensusthathumansaretheleadingcauseofclimatechange.Intheirlatestreport,theIntergovernmentalPanelonClimateChangestatedunequivocally thathumanactivityisthecauseofglobalwarming. NaturalclimatecyclescanchangethetemperatureofEarth,butthechangesweareseeingarehappeningatascaleandspeedthatnaturalcyclescannotexplain.Thesecyclesaffecttheglobaltemperatureforyears,orsometimesjustmonths,notthe100yearsthatwehaveobserved.Meanwhile,longer-termchangeslikeMilankovitchcyclesandsolarirradiancetakethousandsandthousandsofyears. Therearelotsofthingsthataffectclimatechange,buttheevidenceisirrefutable.Humanactivity,suchasburningfossilfuelsandchanginghowweusetheland,istheleadingcauseofclimatechange. Relatedlinks Whatisclimatechange? Effectsofclimatechange Climatechangequestions UKclimate Climatescience Organisationsandreports Helpusimproveourwebsite Takeourshortsurvey