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Thiswebsitewouldliketoremindyou:Yourbrowser(AppleSafari4)isoutofdate.Updateyourbrowserformore security,comfortandthebestexperienceonthissite. × EncyclopedicEntry globalwarming Forthecompleteencyclopedicentrywithmediaresources,visit: http://education.nationalgeographic.com/encyclopedia/global-warming/ GlobalwarmingdescribesthecurrentriseintheaveragetemperatureofEarth’sairandoceans.Globalwarmingis oftendescribedasthemostrecentexampleofclimatechange. Earth’sclimatehaschangedmanytimes.Ourplanethasgonethroughmultipleiceages,inwhichicesheetsand glacierscoveredlargeportionsoftheEarth.Ithasalsogonethroughwarmperiodswhentemperatureswere higherthantheyaretoday. PastchangesinEarth’stemperaturehappenedveryslowly,overhundredsofthousandsofyears.However,the recentwarmingtrendishappeningmuchfasterthaniteverhas.Naturalcyclesofwarmingandcoolingarenot enoughtoexplaintheamountofwarmingwehaveexperiencedinsuchashorttime—onlyhumanactivitiescan accountforit.Scientistsworrythattheclimateischangingfasterthansomelivingthingscanadapttoit. In1988,theWorldMeteorologicalOrganizationandtheUnitedNationsEnvironmentProgrammeestablisheda committeeofclimatologists,meteorologists,geographers,andotherscientistsfromaroundtheworld.This IntergovernmentalPanelonClimateChange(IPCC)includesthousandsofscientistswhoreviewthemostup-todateresearchavailablerelatedtoglobalwarmingandclimatechange.TheIPCCevaluatestheriskofclimate changecausedbyhumanactivities. AccordingtotheIPCC’smostrecentreport(in2007),Earth’saveragesurfacetemperatureshaverisenabout0.74 degreesCelsius(1.33degreesFahrenheit)duringthepast100years.Theincreaseisgreaterinnorthern latitudes.TheIPCCalsofoundthatlandregionsarewarmingfasterthanoceans.TheIPCCstatesthatmostofthe temperatureincreasesincethemid-20thcenturyislikelyduetohumanactivities. TheGreenhouseEffect Humanactivitiescontributetoglobalwarmingbyincreasingthegreenhouseeffect.Thegreenhouseeffect happenswhencertaingases—knownasgreenhousegases—collectinEarth’satmosphere.Thesegases,which occurnaturallyintheatmosphere,includecarbondioxide,methane,nitrogenoxide,andfluorinatedgases sometimesknownaschlorofluorocarbons(CFCs). Greenhousegasesletthesun’slightshineontotheEarth’ssurface,buttheytraptheheatthatreflectsbackupinto theatmosphere.Inthisway,theyactliketheinsulatingglasswallsofagreenhouse.Thegreenhouseeffectkeeps Earth’sclimatecomfortable.Withoutit,surfacetemperatureswouldbecoolerbyabout33degreesCelsius(60 degreesFahrenheit),andmanylifeformswouldfreeze. SincetheIndustrialRevolutioninthelate1700sandearly1800s,peoplehavebeenreleasinglargequantitiesof greenhousegasesintotheatmosphere.Thatamounthasskyrocketedinthepastcentury.Greenhousegas 1of9 emissionsincreased70percentbetween1970and2004.Emissionsofcarbondioxide,themostimportant greenhousegas,rosebyabout80percentduringthattime.Theamountofcarbondioxideintheatmosphere todayfarexceedsthenaturalrangeseenoverthelast650,000years. Mostofthecarbondioxidethatpeopleputintotheatmospherecomesfromburningfossilfuelssuchasoil,coal, andnaturalgas.Cars,trucks,trains,andplanesallburnfossilfuels.Manyelectricpowerplantsalsoburnfossil fuels. Anotherwaypeoplereleasecarbondioxideintotheatmosphereisbycuttingdownforests.Thishappensfortwo reasons.Decayingplantmaterial,includingtrees,releasestonsofcarbondioxideintotheatmosphere.Livingtrees absorbcarbondioxide.Bydiminishingthenumberoftreestoabsorbcarbondioxide,thegasremainsinthe atmosphere. Mostmethaneintheatmospherecomesfromlivestockfarming,landfills,andfossilfuelproductionsuchascoal miningandnaturalgasprocessing.Nitrousoxidecomesfromagriculturaltechnologyandfossilfuelburning. Fluorinatedgasesincludechlorofluorocarbons,hydrochlorofluorocarbons,andhydrofluorocarbons.These greenhousegasesareusedinaerosolcansandrefrigeration. Allofthesehumanactivitiesaddgreenhousegasestotheatmosphere,trappingmoreheatthanusualand contributingtoglobalwarming. EffectsofGlobalWarming Evenslightrisesinaverageglobaltemperaturescanhavehugeeffects.Perhapsthebiggest,mostobviouseffect isthatglaciersandicecapsmeltfasterthanusual.Themeltwaterdrainsintotheoceans,causingsealevelstorise andoceanstobecomelesssalty. Icesheetsandglaciersadvanceandretreatnaturally.AsEarth’stemperaturehaschanged,theicesheetshave grownandshrunk,andsealevelshavefallenandrisen.AncientcoralsfoundonlandinFlorida,Bermuda,andthe Bahamasshowthatthesealevelmusthavebeen5to6meters(16-20feet)higher130,000yearsagothanitis today.Earthdoesn’tneedtobecomeoven-hottomelttheglaciers.Northernsummerswerejust3to5degrees Celsius(5-9degreesFahrenheit)warmerduringthetimeofthoseancientfossilsthantheyaretoday. However,thespeedatwhichglobalwarmingistakingplaceisunprecedented.Theeffectsareunknown. Glaciersandicecapscoverabout10percentoftheworld’slandmasstoday.Theyholdabout75percentofthe world’sfreshwater.Ifallofthisicemelted,sealevelswouldrisebyabout70meters(230feet).TheIPCCreported thattheglobalsealevelroseabout1.8millimeters(0.07inches)peryearfrom1961to1993,and3.1millimeters (0.12inches)peryearsince1993. Risingsealevelscouldfloodcoastalcommunities,displacingmillionsofpeopleinareassuchasBangladesh,the Netherlands,andtheU.S.stateofFlorida.Forcedmigrationwouldimpactnotonlythoseareas,buttheregionsto whichthe“climaterefugees”flee.MillionsmorepeopleincountrieslikeBolivia,Peru,andIndiadependonglacial meltwaterfordrinking,irrigation,andhydroelectricpower.Rapidlossoftheseglacierswoulddevastatethose countries. Glacialmelthasalreadyraisedtheglobalsealevelslightly.However,scientistsarediscoveringwaysthesealevel couldincreaseevenfaster.Forexample,themeltingoftheChacaltayaGlacierinBoliviahasexposeddarkrocks beneathit.Therocksabsorbheatfromthesun,speedingupthemeltingprocess. 2of9 Manyscientistsusetheterm“climatechange”insteadof“globalwarming.”Thisisbecausegreenhousegas emissionsaffectmorethanjusttemperature.Anothereffectinvolveschangesinprecipitationlikerainandsnow. Patternsinprecipitationmaychangeorbecomemoreextreme.Overthecourseofthe20thcentury,precipitation increasedineasternpartsofNorthandSouthAmerica,northernEurope,andnorthernandcentralAsia.However, ithasdecreasedinpartsofAfrica,theMediterranean,andpartsofsouthernAsia. FutureChanges Nobodycanlookintoacrystalballandpredictthefuturewithcertainty.However,scientistscanmakeestimates aboutfuturepopulationgrowth,greenhousegasemissions,andotherfactorsthataffectclimate.Theycanenter thoseestimatesintocomputermodelstofindoutthemostlikelyeffectsofglobalwarming. TheIPCCpredictsthatgreenhousegasemissionswillcontinuetoincreaseoverthenextfewdecades.Asaresult, theypredicttheaverageglobaltemperaturewillincreasebyabout0.2degreesCelsius(0.36degreesFahrenheit) perdecade.Evenifwereducegreenhousegasandaerosolemissionstotheir2000levels,wecanstillexpecta warmingofabout0.1degreeCelsius(0.18degreesFahrenheit)perdecade. Thepanelalsopredictsglobalwarmingwillcontributetosomeseriouschangesinwatersuppliesaroundtheworld. Bythemiddleofthe21stcentury,theIPCCpredicts,riverrunoffandwateravailabilitywillmostlikelyincreaseat highlatitudesandinsometropicalareas.However,manydryregionsinthemid-latitudesandtropicswill experienceadecreaseinwaterresources. Asaresult,millionsofpeoplemaybeexposedtowatershortages.Watershortagesdecreasetheamountofwater availablefordrinking,electricity,andhygiene.Shortagesalsoreducewaterusedforirrigation.Agriculturaloutput wouldslowandfoodpriceswouldclimb.ConsistentyearsofdroughtintheGreatPlainsoftheUnitedStatesand Canadawouldhavethiseffect. IPCCdataalsosuggestthatthefrequencyofheatwavesandextremeprecipitationwillincrease.Weatherpatterns suchasstormsandtropicalcycloneswillbecomemoreintense.Stormsthemselvesmaybestronger,more frequent,andlonger-lasting.Theywouldbefollowedbystrongerstormsurges,theimmediateriseinsealevel followingstorms.Stormsurgesareparticularlydamagingtocoastalareasbecausetheireffects(flooding,erosion, damagetobuildingsandcrops)arelasting. WhatWeCanDo Reducingourgreenhousegasemissionsisacriticalstepinslowingtheglobalwarmingtrend.Manygovernments aroundtheworldareworkingtowardthisgoal. ThebiggesteffortsofarhasbeentheKyotoProtocol,whichwasadoptedin1997andwentintoeffectin2005.By theendof2009,187countrieshadsignedandratifiedtheagreement.Undertheprotocol,37industrialized countriesandtheEuropeanUnionhavecommittedtoreducingtheirgreenhousegasemissions. Thereareseveralwaysthatgovernments,industries,andindividualscanreducegreenhousegases.Wecan improveenergyefficiencyinhomesandbusinesses.Wecanimprovethefuelefficiencyofcarsandothervehicles. Wecanalsosupportdevelopmentofalternativeenergysources,suchassolarpowerandbiofuels,thatdon’t involveburningfossilfuels. Somescientistsareworkingtocapturecarbondioxideandstoreitunderground,ratherthanletitgointothe atmosphere.Thisprocessiscalledcarbonsequestration. 3of9 Treesandotherplantsabsorbcarbondioxideastheygrow.Protectingexistingforestsandplantingnewonescan helpbalancegreenhousegasesintheatmosphere. Changesinfarmingpracticescouldalsoreducegreenhousegasemissions.Forexample,farmsuselarge amountsofnitrogen-basedfertilizers,whichincreasenitrogenoxideemissionsfromthesoil.Reducingtheuseof thesefertilizerswouldreducetheamountofthisgreenhousegasintheatmosphere. Thewayfarmershandleanimalmanurecanalsohaveaneffectonglobalwarming.Whenmanureisstoredas liquidorslurryinpondsortanks,itreleasesmethane.Whenitdriesasasolid,however,itdoesnot. Reducinggreenhousegasemissionsisvitallyimportant.However,theglobaltemperaturehasalreadychanged andwillmostlikelycontinuetochangeforyearstocome.TheIPCCsuggeststhatpeopleexplorewaystoadaptto globalwarmingaswellastrytosloworstopit.Someofthesuggestionsforadaptinginclude: Expandingwatersuppliesthroughraincatchment,conservation,reuse,anddesalination. Adjustingcroplocations,variety,andplantingdates. Buildingseawallsandstormsurgebarriersandcreatingmarshesandwetlandsasbuffersagainstrisingsealevels. Creatingheat-healthactionplans,boostingemergencymedicalservices,andimprovingdiseasesurveillanceandcontrol. Diversifyingtourismattractions,becauseexistingattractionslikeskiresortsandcoralreefsmaydisappear. Planningforroadsandraillinestocopewithwarmingand/orflooding. Strengtheningenergyinfrastructure,improvingenergyefficiency,andreducingdependenceonsinglesourcesofenergy. VOCABULARY Term PartofSpeech Definition abnormal adjective unusual. adapt verb toadjusttonewsurroundingsoranewsituation. aerosolcan noun containerofliquidmaterialunderhighpressure.Whenreleasedthrough asmallopening,theliquidbecomesasprayorfoam. agriculturaltechnology noun theartandscienceofcomplexmachinesusedtoperformtasks associatedwithfarmingandranching. ancient adjective veryold. atmosphere noun layersofgasessurroundingaplanetorothercelestialbody. biofuel noun energysourcederiveddirectlyfromorganicmatter,suchasplants. buffer noun acushionorshield. carbondioxide noun greenhousegasproducedbyanimalsduringrespirationandusedby plantsduringphotosynthesis.Carbondioxideisalsothebyproductof burningfossilfuels. carbonicacid noun chemicalproducedascarbondioxidedissolvesinwater. carbonsequestration noun processofcapturingcarbonemissionsandstoringthemunderground. century noun 100years. chlorofluorocarbon (CFC) noun chemicalcompoundmostlyusedinrefrigerantsandflame-retardants. SomeCFCshavedestructiveeffectsontheozonelayer. climate noun allweatherconditionsforagivenlocationoveraperiodoftime. 4of9 climatechange noun gradualchangesinalltheinterconnectedweatherelementsonour planet. climaterefugee noun personforcedtoleavehisorherhomeandcommunitybecauseof climatechange. climatologist noun personwhostudieslong-termpatternsinweather. coal noun dark,solidfossilfuelminedfromtheearth. coast noun edgeoflandalongtheseaorotherlargebodyofwater. committee noun groupofpeopleelectedorappointedtoperformatask. conservation noun managementofanaturalresourcetopreventexploitation,destruction,or neglect. consistent adjective maintainingasteady,reliablequality. cope verb tohandleordealwithproblems. coral noun tinyoceananimal,someofwhichsecretecalciumcarbonatetoformreefs. coralreef noun rockyoceanfeaturesmadeupofmillionsofcoralskeletons. critical adjective veryimportant. cyclone noun weathersystemthatrotatesaroundacenteroflowpressureandincludes thunderstormsandrain.Usually,hurricanesrefertocyclonesthatform overtheAtlanticOcean. data pluralnoun (singular:datum)informationcollectedduringascientificstudy. decade noun 10years. decay verb torotordecompose. desalination noun processofconvertingseawatertofreshwaterbyremovingsaltand minerals. devastate verb todestroy. diminish verb tobecomesmallerorlessimportant. dissolve verb tobreakupordisintegrate. diverse adjective variedorhavingmanydifferenttypes. drought noun periodofgreatlyreducedprecipitation. electricity noun setofphysicalphenomenaassociatedwiththepresenceandflowof electriccharge. emission noun dischargeorrelease. encore noun reappearancebyaperformeraftertheendoftheperformance. energyefficiency noun useofarelativelysmallamountofenergyforagiventask,purpose,or service;achievingaspecificoutputwithlessenergyinput. erosion noun actinwhichearthiswornaway,oftenbywater,wind,orice. establish verb toformorofficiallyorganize. 5of9 EuropeanUnion noun associationofEuropeannationspromotingfreetrade,easeof transportation,andculturalandpoliticallinks. evaluate verb todecidesomething'sworth. farming noun theart,science,andbusinessofcultivatingthelandforgrowingcrops. fertilizer noun nutrient-richchemicalsubstance(naturalormanmade)appliedtosoilto encourageplantgrowth. flee verb torunaway. fluorinate verb toaddorcombinewiththeelementfluorine(F). forest noun ecosystemfilledwithtreesandunderbrush. fossil noun remnant,impression,ortraceofanancientorganism. fossilfuel noun coal,oil,ornaturalgas.Fossilfuelsformedfromtheremainsofancient plantsandanimals. freeze noun weatherpatternoftemperaturesbelow0degreesCelsius(32degrees Fahrenheit). fuelefficiency noun abilitytoproduceasmuchpowerwithaslittlefuelconsumedaspossible. geographer noun personwhostudiesplacesandtherelationshipsbetweenpeopleand theirenvironments. glacier noun massoficethatmovesslowlyoverland. globalwarming noun increaseintheaveragetemperatureoftheEarth'sairandoceans. GreatPlains noun grasslandregionofNorthAmerica,betweentheRockyMountainsand theMississippiRiver. greenhouse noun building,oftenmadeofglassorotherclearmaterial,usedtohelpplants grow. greenhouseeffect noun phenomenonwheregasesallowsunlighttoenterEarth'satmospherebut makeitdifficultforheattoescape. greenhousegas noun gasintheatmosphere,suchascarbondioxide,methane,watervapor, andozone,thatabsorbssolarheatreflectedbythesurfaceoftheEarth, warmingtheatmosphere. heat-healthactionplan noun publicsystemforpreventingorreducingdeathanddiseasedueto extremeheatwaves. heatwave noun periodofunusuallyhotweather. hydrochlorofluorocarbon noun greenhousegasoftenusedasanindustrialcoolingmaterial. hydroelectricpower noun usableenergygeneratedbymovingwaterconvertedtoelectricity. hygiene noun scienceandmethodsofkeepingcleanandhealthy. iceage noun longperiodofcoldclimatewhereglacierscoverlargepartsoftheEarth. Thelasticeagepeakedabout20,000yearsago.Alsocalledglacialage. icecap noun areaoffewerthan50,000squarekilometers(19,000squaremiles) coveredbyice. icesheet noun thicklayerofglacialicethatcoversalargeareaofland. 6of9 industrialization noun growthofmachineproductionandfactories. IndustrialRevolution noun changeineconomicandsocialactivities,beginninginthe18thcentury, broughtbythereplacementofhandtoolswithmachineryandmass production. infrastructure noun structuresandfacilitiesnecessaryforthefunctioningofasociety,suchas roads. insect noun typeofanimalthatbreathesairandhasabodydividedintothree segments,withsixlegsandusuallywings. IntergovernmentalPanel onClimateChange (IPCC) noun groupofscientistswhoreviewthemostup-to-dateresearchavailable relatedtoglobalwarmingandclimatechange. irrigation noun wateringland,usuallyforagriculture,byartificialmeans. KyotoProtocol noun (1997)internationalagreementtoreducegreenhousegasemissions. landfill noun sitewheregarbageislayeredwithdirtandotherabsorbingmaterialto preventcontaminationofthesurroundinglandorwater. landmass noun largeareaofland. latitude noun distancenorthorsouthoftheEquator,measuredindegrees. livestock animalsraisedforsaleandprofit. manure noun,plural noun noun marsh noun wetlandareausuallycoveredbyashallowlayerofseawateror freshwater. meltwater noun freshwaterthatcomesfrommeltingsnoworice. meteorologist noun personwhostudiespatternsandchangesinEarth'satmosphere. methane noun chemicalcompoundthatisthebasicingredientofnaturalgas. migration noun movementofagroupofpeopleoranimalsfromoneplacetoanother. model noun imageorimpressionofanobjectusedtorepresenttheobjectorsystem. multiple adjective many. naturalgas noun typeoffossilfuelmadeupmostlyofthegasmethane. nitrogen noun chemicalelementwiththesymbolN,whosegasformis78%ofthe Earth'satmosphere. nitrousoxide noun greenhousegasusedinmedicineandthemanufactureofrockets.Also knownaslaughinggasorhappygas. oil noun fossilfuelformedfromtheremainsofmarineplantsandanimals.Also knownaspetroleumorcrudeoil. penguin noun birdnativetotheAntarctic. powerplant noun industrialfacilityforthegenerationofelectricenergy. precipitation noun allformsinwhichwaterfallstoEarthfromtheatmosphere. protocol noun seriesofrules. animalexcrementorwasteusedtofertilizesoil. 7of9 raincatchment noun systemtocollectandstorerainwater. ratify verb toformallyapproveorconfirm. refrigerant noun substanceusedtokeepmaterialscool. research noun scientificobservationsandinvestigationintoasubject,usuallyfollowing thescientificmethod:observation,hypothesis,prediction, experimentation,analysis,andconclusion. runoff noun overflowoffluidfromafarmorindustrialfactory. sealevel noun baselevelformeasuringelevations.Sealevelisdeterminedby measurementstakenovera19-yearcycle. seawall noun barrierbuilttoprotectabeachorshorelinefromerosion.Alsocalleda bulkhead. skiresort noun facilitywherepeoplecanskiforrecreationorsport. skyrocket verb toincreaserapidly. slurry noun liquidwaste,suchasthatfromthecoalminingandcleaningprocess,also calledsludge. snow noun precipitationmadeoficecrystals. solarpower noun rateofproducing,transferring,orusingsolarenergy. spruce noun coniferous,orcone-bearing,tree. storm noun severeweatherindicatingadisturbedstateoftheatmosphereresulting fromupliftedair. stormsurge noun abnormalriseinsealevelaccompanyingahurricaneorotherintense storm.Alsocalledastormtide. stormsurgebarrier noun wallsorobstaclesbuilttopreventoceanorriverwaterfromflowinginto anareaafterastorm.Alsocalledleveeorfloodgate. surveillance noun observationofaperson,community,orsituation. temperature noun degreeofhotnessorcoldnessmeasuredbyathermometerwitha numericalscale. tourism noun theindustry(includingfood,hotels,andentertainment)oftravelingfor pleasure. tropical adjective existinginthetropics,thelatitudesbetweentheTropicofCancerinthe northandtheTropicofCapricorninthesouth. UnitedNations Environment Programme noun organizationwhosemissionistoprovideinternationalleadershipand encouragepartnershipsincaringfortheenvironment. unprecedented adjective neverbeforeknownorexperienced. vital adjective necessaryorveryimportant. watershortage noun reductionintheamountoffreshwateravailablefordrinking,hygiene,and industrialandagriculturaluse. 8of9 watersupply noun amountofavailablefreshwaterfordrinking,hygiene,andindustrialand agriculturaluse. weatherpattern noun repeatingorpredictablechangesintheEarth'satmosphere,suchas winds,precipitation,andtemperatures. wetland noun areaoflandcoveredbyshallowwaterorsaturatedbywater. WorldMeteorological Organization noun UnitedNationsagencythatstudiestheEarth'satmosphere,itsinteraction withtheoceans,theclimate,andthedistributionofwaterresources. ForFurtherExploration Audio&Video NationalGeographicVideo:GlobalWarming101 Images FoodandAgricultureOrganization:FactFile—GlobalWarming Worksheets&Handouts UnitedNationsEnvironmentProgramme:ClimateChangeToolkit Websites NationalGeographicEnvironment:GlobalWarming ©1996–2015NationalGeographicSociety.Allrightsreserved. 9of9