第十四章人类活动对气候的影响

全球气候系统GlobalClimateSystem第十四章人类活动的气候影响什么是温室效应?地球大气中有哪些温室气体?温室气体从何处来?温室效应很不好,是吗?近百年的气候变化有多少是温室效应造成的?如果CO2加倍全球温度会上升多少?21世纪气候会怎样?不确定性有多大?(有关全球变暖的争论)地球大气中有哪些温室气体?温室气体从何处来?Halocarbonsarecarbon-basedcompoundsthatcontainchlorine,fluorine,bromine,oriodine.

TheCFC's,halons(bromine-containingCFC's),hydrofluorocarbons(HFCs),chloroform(CHCl3)andcarbontertrachloride(CCl4)areexclusivelyofindustrialoriginanddidnotexistpriorto60yearsago.

Halocarbonsareresponsiblefortheenvironmentalproblemofstratosphericozonedepletionandseveralofthecompoundsarestronggreenhousegases.

CFC'sarefarlessabundantintheatmospherethanCO2butare10,000timesmorepowerfulasgreenhousegases.ProportionofCFC'shasdeclinedsincebanningoftheirusein1984.

AnnualglobalemissionsofthehalocarbonsCFC-11(filledblacksquares)andCFC-12(opensquares)totheatmospherefrom1972to1992,principallyfromtheiruseasrefrigerantsandagentsfortheblowingoffoam.NoticethedeclineinemissionsfollowingenactmentoftheMontrealProtocolin1987.(AfterWorldMeteorologicalOrganization,1994).

ConcentrationsofCarbonDioxide.Atmosphericcarbondioxideconcentrationinpartspermillion(ppm)asrecordedatfivesites(datafromBradleyandJones,1995).温室效应很可怕,是吗?近百年的气候变化有多少是温室效应造成的?气候系统对各种强迫的敏感性的不确定性2xCO2~4W/m2~1.2C(withoutfeed-backs)actualvalue=~3C(1.5-4.5C)???21世纪气候会怎样??是祸还是福?何种对策?全球变暖的有关争论Table1.KeyDifferenceswithSkeptics1.Observedglobalwarming:realormeasurementproblem?Hansen:globalwarmingis0.5-0.75°Cinpastcentury,atleast~0.3°Cinpast25years.Lindzen:sinceabout1850"...morelikely...0.1±0.3°C"(MITTechTalk,34,#7,1989).2.Climatesensitivity(equilibriumresponseto2xCO2)Lindzen:~<1°CHansen:3±1°CComments:paleoclimatedata,improvedclimatemodels,andprocessstudiesmaynarrowuncertainties;observedclimatechangeondecadaltimescaleswillprovideconstraintifclimateforcingsaremeasured;implicitinformationonclimatesensitivitycanbeextractedfromobservedchangesinoceanheatstorage.

3.Watervaporfeedback

Lindzen:negative,uppertroposphericwatervapordecreaseswithglobalwarming.Hansen:positive,upperandlowertroposphericwatervaporincreasewithglobalwarming.References:(theseincludereferencesbyLindzenstatingthat,inresponsetoglobalwarming,watervaporwilldecreaseataltitudesabove2-3km).Comment:accurateobservationsofinterannualchanges(severalyears)andlong-termchanges(1-2decades)ofuppertroposphericwatervaporcouldprovidedefiningdata.4.CO2contributiontothe~33°CnaturalgreenhouseeffectLindzen:"Evenifallothergreenhousegases(suchascarbondioxideandmethane)weretodisappear,wewouldstillbeleftwithover98percentofthecurrentgreenhouseeffect."CatoReview,Springissue,87-98,1992;"IfallCO2wereremovedfromtheatmosphere,watervaporandcloudswouldstillprovidealmostallofthepresentgreenhouseeffect."Res.Explor.9,191-200,1993.

LacisandHansen:removingCO2,withwatervaporkeptfixed,wouldcooltheEarth5-10°C;removingCO2andtracegaseswithwatervaporallowedtorespondwouldremovemostofthenaturalgreenhouseeffect.5.Whenwillglobalwarmingandclimatechangebeobvious?Lindzen:Ipersonallyfeelthatthelikelihoodoverthenextcentury[21stcentury]ofgreenhousewarmingreachingmagnitudescomparabletonaturalvariabilityremainssmall.Hansen:"Withtheclimatologicalprobabilityofahotsummerrepresentedbytwofaces(saypaintedred)ofasix-faceddie,judgingfromourmodelbythe1990sthreeorfourofthesixdiefaceswillbered.Itseemstousthatthisisasufficient'loading'ofthedicethatitwillbenoticeabletothemaninthestreet."J.Geophys.Res.93,9341-9364,1988.6.Planetarydisequilibrium

Hansen:Earthisoutofradiativeequilibriumwithspacebyatleastapproximately0.5W/m2(absorbingmoreenergythanitemits).Comments:Thisisthemostfundamentalmeasureofthestateofthegreenhouseeffect.Becausethedisequilibriumisaproductofthelongresponsetimeoftheclimatesystem,whichinturnisastrongfunctionofclimatesensitivity,confirmationofthedisequilibriumprovidesinformationonclimatesensitivityandanindicationofhowmuchadditionalglobalwarmingis"inthepipeline"duetogasesalreadyaddedtotheatmosphere.Thisdisequilibriumcouldbemeasuredasthesumoftherateofheatstorageintheoceanplusthenetenergygoingintoth