Vital Signs of the Planet - Causes | Facts – Climate Change

Human activities (primarily the burning of fossil fuels) have fundamentally increased the concentration of greenhouse gases in Earth's atmosphere, warming the ... Facts Evidence Causes Effects ScientificConsensus VitalSigns Questions(FAQ) Evidence Causes Effects ScientificConsensus VitalSigns Questions(FAQ) ›enespañol InBrief: Humanactivities(primarilytheburningoffossilfuels)havefundamentallyincreasedtheconcentrationofgreenhousegasesinEarth’satmosphere,warmingtheplanet.Naturaldrivers,withouthumanintervention,wouldpushourplanettowardacoolingperiod. Scientistsattributetheglobalwarmingtrendobservedsincethemid-20thcenturytothehumanexpansionofthe"greenhouseeffect"1—warmingthatresultswhentheatmospheretrapsheatradiatingfromEarthtowardspace. Certaingasesintheatmosphereblockheatfromescaping.Long-livedgasesthatremainsemi-permanentlyintheatmosphereanddonotrespondphysicallyorchemicallytochangesintemperaturearedescribedas"forcing"climatechange.Gases,suchaswatervapor,whichrespondphysicallyorchemicallytochangesintemperatureareseenas"feedbacks." Gasesthatcontributetothegreenhouseeffectinclude: Watervapor.Themostabundantgreenhousegas,butimportantly,itactsasafeedbacktotheclimate.WatervaporincreasesastheEarth'satmospherewarms,butsodoesthepossibilityofcloudsandprecipitation,makingthesesomeofthemostimportantfeedbackmechanismstothegreenhouseeffect. Carbondioxide(CO2).Aminorbutveryimportantcomponentoftheatmosphere,carbondioxideisreleasedthroughnaturalprocessessuchasrespirationandvolcanoeruptionsandthroughhumanactivitiessuchasdeforestation,landusechanges,andburningfossilfuels.HumanshaveincreasedatmosphericCO2concentrationby48%sincetheIndustrialRevolutionbegan.Thisisthemostimportantlong-lived"forcing"ofclimatechange. Methane.Ahydrocarbongasproducedboththroughnaturalsourcesandhumanactivities,includingthedecompositionofwastesinlandfills,agriculture,andespeciallyricecultivation,aswellasruminantdigestionandmanuremanagementassociatedwithdomesticlivestock.Onamolecule-for-moleculebasis,methaneisafarmoreactivegreenhousegasthancarbondioxide,butalsoonewhichismuchlessabundantintheatmosphere. Nitrousoxide.Apowerfulgreenhousegasproducedbysoilcultivationpractices,especiallytheuseofcommercialandorganicfertilizers,fossilfuelcombustion,nitricacidproduction,andbiomassburning. Chlorofluorocarbons(CFCs).Syntheticcompoundsentirelyofindustrialoriginusedinanumberofapplications,butnowlargelyregulatedinproductionandreleasetotheatmospherebyinternationalagreementfortheirabilitytocontributetodestructionoftheozonelayer.Theyarealsogreenhousegases. Notenoughgreenhouseeffect:TheplanetMarshasaverythinatmosphere,nearlyallcarbondioxide.Becauseofthelowatmosphericpressure,andwithlittletonomethaneorwatervaportoreinforcetheweakgreenhouseeffect,Marshasalargelyfrozensurfacethatshowsnoevidenceoflife. Toomuchgreenhouseeffect:TheatmosphereofVenus,likeMars,isnearlyallcarbondioxide.ButVenushasabout154,000timesasmuchcarbondioxideinitsatmosphereasEarth(andabout19,000timesasmuchasMarsdoes),producingarunawaygreenhouseeffectandasurfacetemperaturehotenoughtomeltlead. OnEarth,humanactivitiesarechangingthenaturalgreenhouse.Overthelastcenturytheburningoffossilfuelslikecoalandoilhasincreasedtheconcentrationofatmosphericcarbondioxide(CO2).ThishappensbecausethecoaloroilburningprocesscombinescarbonwithoxygenintheairtomakeCO2.Toalesserextent,theclearingoflandforagriculture,industry,andotherhumanactivitieshasincreasedconcentrationsofgreenhousegases. Theconsequencesofchangingthenaturalatmosphericgreenhousearedifficulttopredict,butsomeeffectsseemlikely: Onaverage,Earthwillbecomewarmer.Someregionsmaywelcomewarmertemperatures,butothersmaynot. Warmerconditionswillprobablyleadtomoreevaporationandprecipitationoverall,butindividualregionswillvary,somebecomingwetterandothersdryer. Astrongergreenhouseeffectwillwarmtheoceanandpartiallymeltglaciersandicesheets,increasingsealevel.Oceanwateralsowillexpandifitwarms,contributingfurthertosealevelrise. Outsideofagreenhouse,higheratmosphericcarbondioxide(CO2)levelscanhavebothpositiveandnegativeeffectsoncropyields.SomelaboratoryexperimentssuggestthatelevatedCO2levelscanincreaseplantgrowth.However,otherfactors,suchaschangingtemperatures,ozone,andwaterandnutrientconstraints,maymorethancounteractanypotentialincreaseinyield.Ifoptimaltemperaturerangesforsomecropsareexceeded,earlierpossiblegainsinyieldmaybereducedorreversedaltogether. Climateextremes,suchasdroughts,floodsandextremetemperatures,canleadtocroplossesandthreatenthelivelihoodsofagriculturalproducersandthefoodsecurityofcommunitiesworldwide.Dependingonthecropandecosystem,weeds,pests,andfungicanalsothriveunderwarmertemperatures,wetterclimates,andincreasedCO2levels,andclimatechangewilllikelyincreaseweedsandpests. Finally,althoughrisingCO2canstimulateplantgrowth,researchhasshownthatitcanalsoreducethenutritionalvalueofmostfoodcropsbyreducingtheconcentrationsofproteinandessentialmineralsinmostplantspecies.Climatechangecancausenewpatternsofpestsanddiseasestoemerge,affectingplants,animalsandhumans,andposingnewrisksforfoodsecurity,foodsafetyandhumanhealth.2 TheRoleofHumanActivity InitsFifthAssessmentReport,theIntergovernmentalPanelonClimateChange,agroupof1,300independentscientificexpertsfromcountriesallovertheworldundertheauspicesoftheUnitedNations,concludedthere'samorethan95percentprobabilitythathumanactivitiesoverthepast50yearshavewarmedourplanet. Theindustrialactivitiesthatourmoderncivilizationdependsuponhaveraisedatmosphericcarbondioxidelevelsfrom280partspermilliontoabout417partspermillioninthelast151years.Thepanelalsoconcludedthere'sabetterthan95percentprobabilitythathuman-producedgreenhousegasessuchascarbondioxide,methaneandnitrousoxidehavecausedmuchoftheobservedincreaseinEarth'stemperaturesoverthepast50-plusyears. Thepanel'sfullSummaryforPolicymakersreportisonlineathttps://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_summary-for-policymakers.pdf. SolarIrradiance Theabovegraphcomparesglobalsurfacetemperaturechanges(redline)andtheSun'senergythatEarthreceives(yellowline)inwatts(unitsofenergy)persquaremetersince1880.Thelighter/thinnerlinesshowtheyearlylevelswhiletheheavier/thickerlinesshowthe11-yearaveragetrends.Eleven-yearaveragesareusedtoreducetheyear-to-yearnaturalnoiseinthedata,makingtheunderlyingtrendsmoreobvious. TheamountofsolarenergythatEarthreceiveshasfollowedtheSun’snatural11-yearcycleofsmallupsanddownswithnonetincreasesincethe1950s.Overthesameperiod,globaltemperaturehasrisenmarkedly.ItisthereforeextremelyunlikelythattheSunhascausedtheobservedglobaltemperaturewarmingtrendoverthepasthalf-century.Credit:NASA/JPL-Caltech It'sreasonabletoassumethatchangesintheSun'senergyoutputwouldcausetheclimatetochange,sincetheSunisthefundamentalsourceofenergythatdrivesourclimatesystem. Indeed,studiesshowthatsolarvariabilityhasplayedaroleinpastclimatechanges.Forexample,adecreaseinsolaractivitycoupledwithanincreaseinvolcanicactivityisthoughttohavehelpedtriggertheLittleIceAgebetweenapproximately1650and1850,whenGreenlandcooledfrom1410tothe1720sandglaciersadvancedintheAlps. ButseverallinesofevidenceshowthatcurrentglobalwarmingcannotbeexplainedbychangesinenergyfromtheSun: Since1750,theaverageamountofenergycomingfromtheSuneitherremainedconstantorincreasedslightly. IfthewarmingwerecausedbyamoreactiveSun,thenscientistswouldexpecttoseewarmertemperaturesinalllayersoftheatmosphere.Instead,theyhaveobservedacoolingintheupperatmosphere,andawarmingatthesurfaceandinthelowerpartsoftheatmosphere.That'sbecausegreenhousegasesaretrappingheatintheloweratmosphere. Climatemodelsthatincludesolarirradiancechangescan’treproducetheobservedtemperaturetrendoverthepastcenturyormorewithoutincludingariseingreenhousegases. References IPCCFifthAssessmentReport,2014 UnitedStatesGlobalChangeResearchProgram,"GlobalClimateChangeImpactsintheUnitedStates,"CambridgeUniversityPress,2009 NaomiOreskes,"TheScientificConsensusonClimateChange,"Science3December2004:Vol.306no.5702p.1686DOI:10.1126/science.1103618 U.S.EnvironmentalProtectionAgency:"ClimateImpactsonAgricultureandFoodSupply" MikeLockwood,“SolarChangeandClimate:anupdateinthelightofthecurrentexceptionalsolarminimum,”ProceedingsoftheRoyalSocietyA,2December2009,doi10.1098/rspa.2009.0519; JudithLean,“Cyclesandtrendsinsolarirradianceandclimate,”WileyInterdisciplinaryReviews:ClimateChange,vol.1,January/February2010,111-122. WeLiveinaGreenhouse LifeonEarthdependsonenergycomingfromtheSun.AbouthalfthelightreachingEarth'satmospherepassesthroughtheairandcloudstothesurface,whereitisabsorbedandthenradiatedupwardintheformofinfraredheat.About90percentofthisheatisthenabsorbedbythegreenhousegasesandradiatedbacktowardthesurface. IstheSuntoBlame? Credit:SOHO-EITConsortium,ESA,NASA HowdoweknowthatchangesintheSunaren’ttoblameforcurrentglobalwarmingtrends? Since1978,aseriesofsatelliteinstrumentshavemeasuredtheenergyoutputoftheSundirectly.Thesatellitedatashowaveryslightdropinsolarirradiance(whichisameasureoftheamountofenergytheSungivesoff)overthistimeperiod.SotheSundoesn'tappeartoberesponsibleforthewarmingtrendobservedoverthepastseveraldecades. Longer-termestimatesofsolarirradiancehavebeenmadeusingsunspotrecordsandotherso-called“proxyindicators,”suchastheamountofcarbonintreerings.Themostrecentanalysesoftheseproxiesindicatethatsolarirradiancechangescannotplausiblyaccountformorethan10percentofthe20thcentury’swarming.2 Latestresources Video:GlobalWarmingfrom1880to2020 Video:OzoneWatch2018 Earth360Video:TheCallofScience ImagesofChange Exploreastunninggalleryofbefore-and-afterimagesofEarthfromlandandspacethatrevealourhomeplanetinastateofflux. ClimateTimeMachine TravelthroughEarth'srecentclimatehistoryandseehowincreasingcarbondioxide,globaltemperatureandseaicehavechangedovertime. EyesontheEarth TrackEarth'svitalsignsfromspaceandflyalongwithNASA'sEarth-observingsatellitesinaninteractive3Dvisualization. GlobalIceViewer Earth'sicecoverisshrinking.Seehowclimatechangehasaffectedglaciers,seaice,andcontinentalicesheets.