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What is Greenhouse Effect ? The “Greenhouse Effect” is a term that refers to a physical property of the Earth's atmosphere. If the Earth had no atmosphere, its average surface temperature would be very low of about 18℃ rather than the comfortable 15℃ found today. The difference in temperature is due to a suite of gases called greenhouse gases which affect the overall energy balance of the Earth's system by absorbing infrared radiation. In its existing state, the Earth atmosphere system balances absorption of solar radiation by emission of infrared radiation to space (Fig. 1). Due to greenhouse gases, the atmosphere absorbs more infrared energy than it reradiates to space, resulting in a net warming of the Earthatmosphere system and of surface temperature. This is the “Natural Greenhouse Effect”. With more greenhouse gases released to the atmosphere due to human activity, more infrared radiation will be trapped in the Earth's surface which contributes to the “Enhanced Greenhouse Effect”. Fig. 1 A simplified diagram illustrating the global longterm radiative balance of the atmosphere. Net input of solar radiation (240 Wm 2 ) must be balanced by net output of infrared radiation. About a third (103 Wm 2 ) of incoming solar radiation is reflected and the remainder is mostly absorbed by the surface. Outgoing infrared radiation is absorbed by greenhouse gases and by clouds keeping the surface about 33℃ warmer than it would otherwise be. Types of Greenhouse gases Greenhouse gases comprise less than 1% of the atmosphere. Their levels are determined by a balance between “sources”and “sinks”. Sources and sinks are processes that generate and destroy greenhouse gases respectively. Human affect greenhouse gas levels by introducing new sources or by interfering with natural sinks. The major greenhouse gases in the atmosphere are carbon dioxide (CO 2 ), methane, (CH 4 ), nitrous oxide (N 2 O), chlorofluorocarbons (CFCs) and ozone (O 3 ). Atmospheric water vapour (H 2 O) also makes a large contribution to the natural greenhouse effect but it is thought that its presence is not directly affected by human activity. Characteristics of some of the greenhouse gases are shown in Table 1. Global Warming Potential (GWP) Different greenhouse gases exert different effects on the Earth's energy balance. In order to assist policymakers to measure the impact of various greenhouse gases on global warming, the concept of Global Warming Potentials (GWPs) was introduced by the Intergovernmental Panel on Climate Change (IPCC) in its 1990 report. GWP reflects the relative strength of individual greenhouse gas with respect to its impact on global warming. It was defined as the cumulative radiative forcing* between the present and some future time caused by a unit mass of greenhouse gas emitted now, expressed relative to CO 2 . The GWPs developed by IPCC for a number of greenhouse gases are shown in Table 2. Global Warming Potentials take into account the differing atmospheric lifetimes and abilities of various gases to absorb radiation. Derivations of GWPs requires knowledge of the fate of the emitted gas (typically not well understood) and the radiative forcing due to the amount remaining in the atmosphere (reasonably well + Climatological Information Services > Climate Change > Green House Effect

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  • WhatisGreenhouseEffect?

    TheGreenhouseEffectisatermthatreferstoaphysicalpropertyoftheEarth'satmosphere.IftheEarthhadnoatmosphere,itsaveragesurfacetemperaturewouldbeverylowofabout18ratherthanthecomfortable15foundtoday.ThedifferenceintemperatureisduetoasuiteofgasescalledgreenhousegaseswhichaffecttheoverallenergybalanceoftheEarth'ssystembyabsorbinginfraredradiation.Initsexistingstate,theEarthatmospheresystembalancesabsorptionofsolarradiationbyemissionofinfraredradiationtospace(Fig.1).Duetogreenhousegases,theatmosphereabsorbsmoreinfraredenergythan

    itreradiatestospace,resultinginanetwarmingoftheEarthatmospheresystemandofsurfacetemperature.ThisistheNaturalGreenhouseEffect.Withmoregreenhousegasesreleasedtotheatmosphereduetohumanactivity,moreinfraredradiationwillbetrappedintheEarth'ssurfacewhichcontributestotheEnhancedGreenhouseEffect.

    Fig.1Asimplifieddiagramillustratingthegloballongtermradiativebalanceoftheatmosphere.Netinputofsolarradiation(240Wm2)mustbebalancedbynetoutputofinfraredradiation.Aboutathird(103Wm2)ofincomingsolarradiationisreflectedandtheremainderismostlyabsorbedbythesurface.Outgoinginfraredradiationisabsorbedbygreenhousegasesandbycloudskeepingthesurfaceabout33warmerthanitwouldotherwisebe.

    TypesofGreenhousegases

    Greenhousegasescompriselessthan1%oftheatmosphere.Theirlevelsaredeterminedbyabalancebetweensourcesandsinks.Sourcesandsinksareprocessesthatgenerateanddestroygreenhousegasesrespectively.Humanaffectgreenhousegaslevelsbyintroducingnewsourcesorbyinterferingwithnaturalsinks.

    Themajorgreenhousegasesintheatmospherearecarbondioxide(CO2),methane,(CH4),nitrousoxide(N2O),chlorofluorocarbons(CFCs)andozone(O3).Atmosphericwatervapour(H2O)alsomakesalargecontributiontothenaturalgreenhouseeffectbutitisthoughtthatitspresenceisnotdirectlyaffectedbyhumanactivity.CharacteristicsofsomeofthegreenhousegasesareshowninTable1.

    GlobalWarmingPotential(GWP)

    DifferentgreenhousegasesexertdifferenteffectsontheEarth'senergybalance.Inordertoassistpolicymakerstomeasuretheimpactofvariousgreenhousegasesonglobalwarming,theconceptofGlobalWarmingPotentials(GWPs)wasintroducedbytheIntergovernmentalPanelonClimateChange(IPCC)inits1990report.GWPreflectstherelativestrengthofindividualgreenhousegaswithrespecttoitsimpactonglobalwarming.Itwasdefinedasthecumulativeradiativeforcing*betweenthepresentandsomefuturetimecausedbyaunitmassofgreenhousegasemittednow,expressedrelativetoCO2.TheGWPsdevelopedbyIPCCforanumberofgreenhousegasesareshowninTable2.

    GlobalWarmingPotentialstakeintoaccountthedifferingatmosphericlifetimesandabilitiesofvariousgasestoabsorbradiation.DerivationsofGWPsrequiresknowledgeofthefateoftheemittedgas(typicallynotwellunderstood)andtheradiativeforcingduetotheamountremainingintheatmosphere(reasonablywellunderstood).Hence,GWPsencompasscertainuncertainty,typically+35%relativetoCO2reference.

    *Radiativeforcingisdefinedasachangeinaveragenetradiationatthetopofthetroposphere(tropopause)duetoachangeineithersolarorinfraredradiation.Aradiativeforcingperturbsthebalancebetweenincomingandoutgoingradiation.ApositiveradiativeforcingtendsonaveragetowarmtheEarth'ssurfaceanegativeradiativeforcingtendsonaveragetocooltheEarth'ssurface.

    Trendsingreenhousegasconcentrations

    a)CarbonDioxide(CO2)

    HighqualityobservationsoftheconcentrationofCO2beganin1958,withflaskmeasurementsattheMaunaLoaObservatoryinHawaii.Fig.2showsthattheaverageannualconcentrationofCO2intheatmospherehasrisenfromabout315ppmv(partpermillionbyvolume)in1958toaround363ppmvin1997.ThereisaclearannualcycleintheMaunaLoadatathatcorrespondstotheannualcycleofplantrespirationintheNorthernHemisphere:CO2concentrationincreaseduringtheFallandWinteranddeclineduringSpringandSummer.Thiscycle,followsthegrowthanddiebackofvegetation,isreversedandofsmalleramplitudeintheSouthernHemisphere,anddisappearsalmostentirelyinthedatameasuredneartheEquator.

    @Fig.2Atmosphericcarbondioxidemonthlymeanmixingratios.DatapriortoMay1974arefromtheScrippsInstitutionofOceanography(),datasinceMay1974arefromtheU.S.NationalOceanicandAtmosphericAdministration().Alongtermtrendcurve()isfittedtothemonthlymeanvalues.

    b)Methane(CH4)

    Therateofincreaseoftheatmosphericabundanceofmethanehasdeclinedoverthelastdecade,slowingdramaticallyin1991to1992,thoughwithanapparentincreaseinthegrowthrateinlate1993(Fig.3).Theaveragetrendover1980to1990isabout13ppbv/year(partperbillionbyvolume/year).

    @Fig.3AtmosphericmethanemixingratiosfromdiscreteairsamplescollectedatMaunaLoa,Hawaii.Asmoothcurve(red)andlongtermtrend(green)arefittedtothemeasurements(blue).

    c)NitrousOxide(N2O)

    Overthelastfourdecades,theaveragegrowthrateofN2Oisabout0.25%/year(Fig.4).CurrenttroposphericconcentrationofN2Oisaround312to314ppbv.

    @Fig.4AtmosphericN2Omixingratios.

    d)Chlorofluorocarbons(CFCs)

    Amongthefamilycompoundsofchlorocarbons,CFCl3(CFC11)andCF2Cl2(CFC12)arereceivingmoreattentionbecauseoftheirlargerconcentrationsandpotentiallysignificanteffectsonstratosphericozone.CFC11andCFC12havethehighestconcentrationsofthemanmadechlorocarbons,around0.27and0.55ppbv,respectively(measuredatMaunaLoain1997,Fig.5&6).AsindicatedintheirGWPvalues,thesetwogasesarestronginfraredabsorbers.ItisthoughtthatCFC11andCFC12havecontributedaboutonethirdoftheradiativeforcingofgasesotherthanCO2duringthe1980s.

    @Fig.5AtmosphericCFC11mixingratio.

    @Fig.6AtmosphericCFC12mixingratios.

    @(Courtesy:MaunaLoaObservatory,Hawaii)

    ConsequencesofEnhancedGreenhouseEffect

    i)GlobalWarming

    Increaseofgreenhousegasesconcentrationcausesareductioninoutgoinginfraredradiation,thustheEarth'sclimatemustchangesomehowtorestorethebalancebetweenincomingandoutgoingradiation.ThisclimaticchangewillincludeaglobalwarmingoftheEarth'ssurfaceandtheloweratmosphereaswarmingupisthesimplestwayfortheclimatetogetridoftheextraenergy.However,asmallriseintemperaturewillinducemanyotherchanges,forexample,cloudcoverandwindpatterns.Someofthesechangesmayacttoenhancethewarming(positivefeedbacks),

    otherstocounteractit(negativefeedbacks).

    Usingcomplexclimatemodels,the"IntergovernmentalPanelonClimateChange"intheirthirdassessmentreporthasforecastthatglobalmeansurfacetemperaturewillriseby1.4to5.8bytheendof2100.Thisprojectiontakesintoaccounttheeffectsofaerosolswhichtendtocooltheclimateaswellasthedelayingeffectsoftheoceanswhichhavealargethermalcapacity.However,therearemanyuncertaintiesassociatedwiththisprojectionsuchasfutureemissionratesofgreenhousegases,climatefeedbacks,andthesizeoftheoceandelay...etc.

    ii)SeaLevelRise

    Ifglobalwarmingtakesplace,sealevelwillriseduetotwodifferentprocesses.Firstly,warmertemperaturecausesealeveltoriseduetothethermalexpansionofseawater.Secondly,waterfrommeltingglaciersandtheicesheetsofGreenlandandtheAntarcticawouldalsoaddwatertotheocean.ItispredictedthattheEarth'saveragesealevelwillriseby0.09to0.88m

    between1990and2100.

    PotentialImpactonhumanlife

    a)EconomicImpact

    Overhalfofthehumanpopulationliveswithin100kilometresofthesea.Mostofthispopulationlivesinurbanareasthatserveasseaports.Ameasurableriseinsealevelwillhaveasevereeconomicimpactonlowlyingcoastalareasandislands,forexamples,increasingthebeacherosionratesalongcoastlines,risingsealeveldisplacingfreshgroundwaterforasubstantialdistanceinland.

    b)AgriculturalImpact

    ExperimentshaveshownthatwithhigherconcentrationsofCO2,plantscangrowbiggerandfaster.However,theeffectofglobalwarmingmayaffecttheatmosphericgeneralcirculationandthusalteringtheglobalprecipitationpatternaswellaschangingthesoilmoisturecontentsovervariouscontinents.Sinceitisunclearhowglobalwarmingwillaffectclimateonaregionalorlocalscale,theprobableeffectsonthebiosphereremainsuncertain.

    c)EffectsonAquaticsystems

    Thelossofcoastalwetlandscouldcertainlyreducefishpopulations,especiallyshellfish.Increasedsalinityinestuariescouldreducetheabundanceoffreshwaterspeciesbutcouldincreasethepresenceofmarinespecies.However,thefullimpactonmarinespeciesisnotknown.

    d)EffectsonHydrologicalCycle

    Globalprecipitationislikelytoincrease.However,itisnotknownhowregionalrainfallpatternswillchange.Someregionsmayhavemorerainfall,whileothersmayhaveless.Furthermore,highertemperatureswouldprobablyincreaseevaporation.Thesechangeswouldprobablycreatenewstressesformanywatermanagementsystems.

    Table1Characteristicsofsomemajorgreenhousegases

    Table2GlobalWarmingPotentials(GWPs)followingtheinstantaneousinjectionof1Kgofeach

    Greenhousegas,relativeto1KgofCO2(BasedonIntergovernmentalPanelonClimateChangeThirdAssessmentReport,2001)

    ClimatologicalInformationServices>ClimateChange>GreenHouseEffect

    Greenhousegas Sources Sinks Importanceforclimate

    CarbonDioxide

    (CO2)

    1)Burningoffossilfuel

    2)Landusechange(deforestation)

    1)OceanUptake

    2)Plantsphotosynthesis

    AbsorbsinfraredradiationaffectsstratosphericO3

    Methane

    (CH4)

    1)Biomassburning

    2)Entericfermentation

    3)Ricepaddies

    1)ReactionswithOH

    2)Microorganismsuptakebysoils

    AbsorbsinfraredradiationaffectstroposphericO3andOHaffectsstratosphericO3andH2OproducesCO2

    NitrousOxide

    (N2O)

    1)Biomassburning

    2)Fossilfuelcombustion

    3)Fertilizers

    1)Removalbysoils

    2)StratosphericphotolysisandreactionwithO

    AbsorbsinfraredradiationaffectsstratosphericO3

    Ozone

    (O3)

    PhotochemicalreactionsinvolvingO2

    CatalyticchemicalreactionsinvolvingNOx,ClOxandHOxspecies.

    Absorbsultravioletandinfraredradiation

    CarbonMonoxide

    (CO)

    1)Plantemissions

    2)Manmaderelease(transport,industrial)

    1)Soiluptake

    2)ReactionswithOH

    AffectsstratosphericO3andOHcyclesproducesCO2

    Chlorofluorocarbons

    (CFCs)

    Industrialproduction Insignificantintroposphere,dissociatedinstratosphere(photolysisandreactionwithO)

    AbsorbsinfraredradiationaffectsstratosphericO3

    SulphurDioxide

    (SO2)

    1)Volcanoes

    2)CoalandBiomassburning

    1)Dryandwetdeposition

    2)ReactionswithOH

    Formsaerosols,whichscattersolarradiation

    Greenhousegas EstimatedLifetime

    (years)

    GlobalWarmingPotential

    20years 100years 500years

    CarbonDioxide(CO2) Variable 1 1 1

    Methane(CH4) 12.0 62 23 7

    NitrousOxide(N2O) 114 275 296 156

    Chlorofluorocarbons(CFCs)

    i) CFCl3(CFC11) 45 6300 4600 1600

    ii) CF2Cl2(CFC12) 100 10200 10600 5200

    iii) CClF3(CFC13) 640 10000 14000 16300

    iv) C2F3Cl3(CFC113) 85 6100 6000 2700

    v) C2F4Cl2(CFC114) 300 7500 9800 8700

    vi) C2F5Cl(CFC115) 1700 4900 7200 9900

  • WhatisGreenhouseEffect?

    TheGreenhouseEffectisatermthatreferstoaphysicalpropertyoftheEarth'satmosphere.IftheEarthhadnoatmosphere,itsaveragesurfacetemperaturewouldbeverylowofabout18ratherthanthecomfortable15foundtoday.ThedifferenceintemperatureisduetoasuiteofgasescalledgreenhousegaseswhichaffecttheoverallenergybalanceoftheEarth'ssystembyabsorbinginfraredradiation.Initsexistingstate,theEarthatmospheresystembalancesabsorptionofsolarradiationbyemissionofinfraredradiationtospace(Fig.1).Duetogreenhousegases,theatmosphereabsorbsmoreinfraredenergythan

    itreradiatestospace,resultinginanetwarmingoftheEarthatmospheresystemandofsurfacetemperature.ThisistheNaturalGreenhouseEffect.Withmoregreenhousegasesreleasedtotheatmosphereduetohumanactivity,moreinfraredradiationwillbetrappedintheEarth'ssurfacewhichcontributestotheEnhancedGreenhouseEffect.

    Fig.1Asimplifieddiagramillustratingthegloballongtermradiativebalanceoftheatmosphere.Netinputofsolarradiation(240Wm2)mustbebalancedbynetoutputofinfraredradiation.Aboutathird(103Wm2)ofincomingsolarradiationisreflectedandtheremainderismostlyabsorbedbythesurface.Outgoinginfraredradiationisabsorbedbygreenhousegasesandbycloudskeepingthesurfaceabout33warmerthanitwouldotherwisebe.

    TypesofGreenhousegases

    Greenhousegasescompriselessthan1%oftheatmosphere.Theirlevelsaredeterminedbyabalancebetweensourcesandsinks.Sourcesandsinksareprocessesthatgenerateanddestroygreenhousegasesrespectively.Humanaffectgreenhousegaslevelsbyintroducingnewsourcesorbyinterferingwithnaturalsinks.

    Themajorgreenhousegasesintheatmospherearecarbondioxide(CO2),methane,(CH4),nitrousoxide(N2O),chlorofluorocarbons(CFCs)andozone(O3).Atmosphericwatervapour(H2O)alsomakesalargecontributiontothenaturalgreenhouseeffectbutitisthoughtthatitspresenceisnotdirectlyaffectedbyhumanactivity.CharacteristicsofsomeofthegreenhousegasesareshowninTable1.

    GlobalWarmingPotential(GWP)

    DifferentgreenhousegasesexertdifferenteffectsontheEarth'senergybalance.Inordertoassistpolicymakerstomeasuretheimpactofvariousgreenhousegasesonglobalwarming,theconceptofGlobalWarmingPotentials(GWPs)wasintroducedbytheIntergovernmentalPanelonClimateChange(IPCC)inits1990report.GWPreflectstherelativestrengthofindividualgreenhousegaswithrespecttoitsimpactonglobalwarming.Itwasdefinedasthecumulativeradiativeforcing*betweenthepresentandsomefuturetimecausedbyaunitmassofgreenhousegasemittednow,expressedrelativetoCO2.TheGWPsdevelopedbyIPCCforanumberofgreenhousegasesareshowninTable2.

    GlobalWarmingPotentialstakeintoaccountthedifferingatmosphericlifetimesandabilitiesofvariousgasestoabsorbradiation.DerivationsofGWPsrequiresknowledgeofthefateoftheemittedgas(typicallynotwellunderstood)andtheradiativeforcingduetotheamountremainingintheatmosphere(reasonablywellunderstood).Hence,GWPsencompasscertainuncertainty,typically+35%relativetoCO2reference.

    *Radiativeforcingisdefinedasachangeinaveragenetradiationatthetopofthetroposphere(tropopause)duetoachangeineithersolarorinfraredradiation.Aradiativeforcingperturbsthebalancebetweenincomingandoutgoingradiation.ApositiveradiativeforcingtendsonaveragetowarmtheEarth'ssurfaceanegativeradiativeforcingtendsonaveragetocooltheEarth'ssurface.

    Trendsingreenhousegasconcentrations

    a)CarbonDioxide(CO2)

    HighqualityobservationsoftheconcentrationofCO2beganin1958,withflaskmeasurementsattheMaunaLoaObservatoryinHawaii.Fig.2showsthattheaverageannualconcentrationofCO2intheatmospherehasrisenfromabout315ppmv(partpermillionbyvolume)in1958toaround363ppmvin1997.ThereisaclearannualcycleintheMaunaLoadatathatcorrespondstotheannualcycleofplantrespirationintheNorthernHemisphere:CO2concentrationincreaseduringtheFallandWinteranddeclineduringSpringandSummer.Thiscycle,followsthegrowthanddiebackofvegetation,isreversedandofsmalleramplitudeintheSouthernHemisphere,anddisappearsalmostentirelyinthedatameasuredneartheEquator.

    @Fig.2Atmosphericcarbondioxidemonthlymeanmixingratios.DatapriortoMay1974arefromtheScrippsInstitutionofOceanography(),datasinceMay1974arefromtheU.S.NationalOceanicandAtmosphericAdministration().Alongtermtrendcurve()isfittedtothemonthlymeanvalues.

    b)Methane(CH4)

    Therateofincreaseoftheatmosphericabundanceofmethanehasdeclinedoverthelastdecade,slowingdramaticallyin1991to1992,thoughwithanapparentincreaseinthegrowthrateinlate1993(Fig.3).Theaveragetrendover1980to1990isabout13ppbv/year(partperbillionbyvolume/year).

    @Fig.3AtmosphericmethanemixingratiosfromdiscreteairsamplescollectedatMaunaLoa,Hawaii.Asmoothcurve(red)andlongtermtrend(green)arefittedtothemeasurements(blue).

    c)NitrousOxide(N2O)

    Overthelastfourdecades,theaveragegrowthrateofN2Oisabout0.25%/year(Fig.4).CurrenttroposphericconcentrationofN2Oisaround312to314ppbv.

    @Fig.4AtmosphericN2Omixingratios.

    d)Chlorofluorocarbons(CFCs)

    Amongthefamilycompoundsofchlorocarbons,CFCl3(CFC11)andCF2Cl2(CFC12)arereceivingmoreattentionbecauseoftheirlargerconcentrationsandpotentiallysignificanteffectsonstratosphericozone.CFC11andCFC12havethehighestconcentrationsofthemanmadechlorocarbons,around0.27and0.55ppbv,respectively(measuredatMaunaLoain1997,Fig.5&6).AsindicatedintheirGWPvalues,thesetwogasesarestronginfraredabsorbers.ItisthoughtthatCFC11andCFC12havecontributedaboutonethirdoftheradiativeforcingofgasesotherthanCO2duringthe1980s.

    @Fig.5AtmosphericCFC11mixingratio.

    @Fig.6AtmosphericCFC12mixingratios.

    @(Courtesy:MaunaLoaObservatory,Hawaii)

    ConsequencesofEnhancedGreenhouseEffect

    i)GlobalWarming

    Increaseofgreenhousegasesconcentrationcausesareductioninoutgoinginfraredradiation,thustheEarth'sclimatemustchangesomehowtorestorethebalancebetweenincomingandoutgoingradiation.ThisclimaticchangewillincludeaglobalwarmingoftheEarth'ssurfaceandtheloweratmosphereaswarmingupisthesimplestwayfortheclimatetogetridoftheextraenergy.However,asmallriseintemperaturewillinducemanyotherchanges,forexample,cloudcoverandwindpatterns.Someofthesechangesmayacttoenhancethewarming(positivefeedbacks),

    otherstocounteractit(negativefeedbacks).

    Usingcomplexclimatemodels,the"IntergovernmentalPanelonClimateChange"intheirthirdassessmentreporthasforecastthatglobalmeansurfacetemperaturewillriseby1.4to5.8bytheendof2100.Thisprojectiontakesintoaccounttheeffectsofaerosolswhichtendtocooltheclimateaswellasthedelayingeffectsoftheoceanswhichhavealargethermalcapacity.However,therearemanyuncertaintiesassociatedwiththisprojectionsuchasfutureemissionratesofgreenhousegases,climatefeedbacks,andthesizeoftheoceandelay...etc.

    ii)SeaLevelRise

    Ifglobalwarmingtakesplace,sealevelwillriseduetotwodifferentprocesses.Firstly,warmertemperaturecausesealeveltoriseduetothethermalexpansionofseawater.Secondly,waterfrommeltingglaciersandtheicesheetsofGreenlandandtheAntarcticawouldalsoaddwatertotheocean.ItispredictedthattheEarth'saveragesealevelwillriseby0.09to0.88m

    between1990and2100.

    PotentialImpactonhumanlife

    a)EconomicImpact

    Overhalfofthehumanpopulationliveswithin100kilometresofthesea.Mostofthispopulationlivesinurbanareasthatserveasseaports.Ameasurableriseinsealevelwillhaveasevereeconomicimpactonlowlyingcoastalareasandislands,forexamples,increasingthebeacherosionratesalongcoastlines,risingsealeveldisplacingfreshgroundwaterforasubstantialdistanceinland.

    b)AgriculturalImpact

    ExperimentshaveshownthatwithhigherconcentrationsofCO2,plantscangrowbiggerandfaster.However,theeffectofglobalwarmingmayaffecttheatmosphericgeneralcirculationandthusalteringtheglobalprecipitationpatternaswellaschangingthesoilmoisturecontentsovervariouscontinents.Sinceitisunclearhowglobalwarmingwillaffectclimateonaregionalorlocalscale,theprobableeffectsonthebiosphereremainsuncertain.

    c)EffectsonAquaticsystems

    Thelossofcoastalwetlandscouldcertainlyreducefishpopulations,especiallyshellfish.Increasedsalinityinestuariescouldreducetheabundanceoffreshwaterspeciesbutcouldincreasethepresenceofmarinespecies.However,thefullimpactonmarinespeciesisnotknown.

    d)EffectsonHydrologicalCycle

    Globalprecipitationislikelytoincrease.However,itisnotknownhowregionalrainfallpatternswillchange.Someregionsmayhavemorerainfall,whileothersmayhaveless.Furthermore,highertemperatureswouldprobablyincreaseevaporation.Thesechangeswouldprobablycreatenewstressesformanywatermanagementsystems.

    Table1Characteristicsofsomemajorgreenhousegases

    Table2GlobalWarmingPotentials(GWPs)followingtheinstantaneousinjectionof1Kgofeach

    Greenhousegas,relativeto1KgofCO2(BasedonIntergovernmentalPanelonClimateChangeThirdAssessmentReport,2001)

    ClimatologicalInformationServices>ClimateChange>GreenHouseEffect

    Greenhousegas Sources Sinks Importanceforclimate

    CarbonDioxide

    (CO2)

    1)Burningoffossilfuel

    2)Landusechange(deforestation)

    1)OceanUptake

    2)Plantsphotosynthesis

    AbsorbsinfraredradiationaffectsstratosphericO3

    Methane

    (CH4)

    1)Biomassburning

    2)Entericfermentation

    3)Ricepaddies

    1)ReactionswithOH

    2)Microorganismsuptakebysoils

    AbsorbsinfraredradiationaffectstroposphericO3andOHaffectsstratosphericO3andH2OproducesCO2

    NitrousOxide

    (N2O)

    1)Biomassburning

    2)Fossilfuelcombustion

    3)Fertilizers

    1)Removalbysoils

    2)StratosphericphotolysisandreactionwithO

    AbsorbsinfraredradiationaffectsstratosphericO3

    Ozone

    (O3)

    PhotochemicalreactionsinvolvingO2

    CatalyticchemicalreactionsinvolvingNOx,ClOxandHOxspecies.

    Absorbsultravioletandinfraredradiation

    CarbonMonoxide

    (CO)

    1)Plantemissions

    2)Manmaderelease(transport,industrial)

    1)Soiluptake

    2)ReactionswithOH

    AffectsstratosphericO3andOHcyclesproducesCO2

    Chlorofluorocarbons

    (CFCs)

    Industrialproduction Insignificantintroposphere,dissociatedinstratosphere(photolysisandreactionwithO)

    AbsorbsinfraredradiationaffectsstratosphericO3

    SulphurDioxide

    (SO2)

    1)Volcanoes

    2)CoalandBiomassburning

    1)Dryandwetdeposition

    2)ReactionswithOH

    Formsaerosols,whichscattersolarradiation

    Greenhousegas EstimatedLifetime

    (years)

    GlobalWarmingPotential

    20years 100years 500years

    CarbonDioxide(CO2) Variable 1 1 1

    Methane(CH4) 12.0 62 23 7

    NitrousOxide(N2O) 114 275 296 156

    Chlorofluorocarbons(CFCs)

    i) CFCl3(CFC11) 45 6300 4600 1600

    ii) CF2Cl2(CFC12) 100 10200 10600 5200

    iii) CClF3(CFC13) 640 10000 14000 16300

    iv) C2F3Cl3(CFC113) 85 6100 6000 2700

    v) C2F4Cl2(CFC114) 300 7500 9800 8700

    vi) C2F5Cl(CFC115) 1700 4900 7200 9900

  • WhatisGreenhouseEffect?

    TheGreenhouseEffectisatermthatreferstoaphysicalpropertyoftheEarth'satmosphere.IftheEarthhadnoatmosphere,itsaveragesurfacetemperaturewouldbeverylowofabout18ratherthanthecomfortable15foundtoday.ThedifferenceintemperatureisduetoasuiteofgasescalledgreenhousegaseswhichaffecttheoverallenergybalanceoftheEarth'ssystembyabsorbinginfraredradiation.Initsexistingstate,theEarthatmospheresystembalancesabsorptionofsolarradiationbyemissionofinfraredradiationtospace(Fig.1).Duetogreenhousegases,theatmosphereabsorbsmoreinfraredenergythan

    itreradiatestospace,resultinginanetwarmingoftheEarthatmospheresystemandofsurfacetemperature.ThisistheNaturalGreenhouseEffect.Withmoregreenhousegasesreleasedtotheatmosphereduetohumanactivity,moreinfraredradiationwillbetrappedintheEarth'ssurfacewhichcontributestotheEnhancedGreenhouseEffect.

    Fig.1Asimplifieddiagramillustratingthegloballongtermradiativebalanceoftheatmosphere.Netinputofsolarradiation(240Wm2)mustbebalancedbynetoutputofinfraredradiation.Aboutathird(103Wm2)ofincomingsolarradiationisreflectedandtheremainderismostlyabsorbedbythesurface.Outgoinginfraredradiationisabsorbedbygreenhousegasesandbycloudskeepingthesurfaceabout33warmerthanitwouldotherwisebe.

    TypesofGreenhousegases

    Greenhousegasescompriselessthan1%oftheatmosphere.Theirlevelsaredeterminedbyabalancebetweensourcesandsinks.Sourcesandsinksareprocessesthatgenerateanddestroygreenhousegasesrespectively.Humanaffectgreenhousegaslevelsbyintroducingnewsourcesorbyinterferingwithnaturalsinks.

    Themajorgreenhousegasesintheatmospherearecarbondioxide(CO2),methane,(CH4),nitrousoxide(N2O),chlorofluorocarbons(CFCs)andozone(O3).Atmosphericwatervapour(H2O)alsomakesalargecontributiontothenaturalgreenhouseeffectbutitisthoughtthatitspresenceisnotdirectlyaffectedbyhumanactivity.CharacteristicsofsomeofthegreenhousegasesareshowninTable1.

    GlobalWarmingPotential(GWP)

    DifferentgreenhousegasesexertdifferenteffectsontheEarth'senergybalance.Inordertoassistpolicymakerstomeasuretheimpactofvariousgreenhousegasesonglobalwarming,theconceptofGlobalWarmingPotentials(GWPs)wasintroducedbytheIntergovernmentalPanelonClimateChange(IPCC)inits1990report.GWPreflectstherelativestrengthofindividualgreenhousegaswithrespecttoitsimpactonglobalwarming.Itwasdefinedasthecumulativeradiativeforcing*betweenthepresentandsomefuturetimecausedbyaunitmassofgreenhousegasemittednow,expressedrelativetoCO2.TheGWPsdevelopedbyIPCCforanumberofgreenhousegasesareshowninTable2.

    GlobalWarmingPotentialstakeintoaccountthedifferingatmosphericlifetimesandabilitiesofvariousgasestoabsorbradiation.DerivationsofGWPsrequiresknowledgeofthefateoftheemittedgas(typicallynotwellunderstood)andtheradiativeforcingduetotheamountremainingintheatmosphere(reasonablywellunderstood).Hence,GWPsencompasscertainuncertainty,typically+35%relativetoCO2reference.

    *Radiativeforcingisdefinedasachangeinaveragenetradiationatthetopofthetroposphere(tropopause)duetoachangeineithersolarorinfraredradiation.Aradiativeforcingperturbsthebalancebetweenincomingandoutgoingradiation.ApositiveradiativeforcingtendsonaveragetowarmtheEarth'ssurfaceanegativeradiativeforcingtendsonaveragetocooltheEarth'ssurface.

    Trendsingreenhousegasconcentrations

    a)CarbonDioxide(CO2)

    HighqualityobservationsoftheconcentrationofCO2beganin1958,withflaskmeasurementsattheMaunaLoaObservatoryinHawaii.Fig.2showsthattheaverageannualconcentrationofCO2intheatmospherehasrisenfromabout315ppmv(partpermillionbyvolume)in1958toaround363ppmvin1997.ThereisaclearannualcycleintheMaunaLoadatathatcorrespondstotheannualcycleofplantrespirationintheNorthernHemisphere:CO2concentrationincreaseduringtheFallandWinteranddeclineduringSpringandSummer.Thiscycle,followsthegrowthanddiebackofvegetation,isreversedandofsmalleramplitudeintheSouthernHemisphere,anddisappearsalmostentirelyinthedatameasuredneartheEquator.

    @Fig.2Atmosphericcarbondioxidemonthlymeanmixingratios.DatapriortoMay1974arefromtheScrippsInstitutionofOceanography(),datasinceMay1974arefromtheU.S.NationalOceanicandAtmosphericAdministration().Alongtermtrendcurve()isfittedtothemonthlymeanvalues.

    b)Methane(CH4)

    Therateofincreaseoftheatmosphericabundanceofmethanehasdeclinedoverthelastdecade,slowingdramaticallyin1991to1992,thoughwithanapparentincreaseinthegrowthrateinlate1993(Fig.3).Theaveragetrendover1980to1990isabout13ppbv/year(partperbillionbyvolume/year).

    @Fig.3AtmosphericmethanemixingratiosfromdiscreteairsamplescollectedatMaunaLoa,Hawaii.Asmoothcurve(red)andlongtermtrend(green)arefittedtothemeasurements(blue).

    c)NitrousOxide(N2O)

    Overthelastfourdecades,theaveragegrowthrateofN2Oisabout0.25%/year(Fig.4).CurrenttroposphericconcentrationofN2Oisaround312to314ppbv.

    @Fig.4AtmosphericN2Omixingratios.

    d)Chlorofluorocarbons(CFCs)

    Amongthefamilycompoundsofchlorocarbons,CFCl3(CFC11)andCF2Cl2(CFC12)arereceivingmoreattentionbecauseoftheirlargerconcentrationsandpotentiallysignificanteffectsonstratosphericozone.CFC11andCFC12havethehighestconcentrationsofthemanmadechlorocarbons,around0.27and0.55ppbv,respectively(measuredatMaunaLoain1997,Fig.5&6).AsindicatedintheirGWPvalues,thesetwogasesarestronginfraredabsorbers.ItisthoughtthatCFC11andCFC12havecontributedaboutonethirdoftheradiativeforcingofgasesotherthanCO2duringthe1980s.

    @Fig.5AtmosphericCFC11mixingratio.

    @Fig.6AtmosphericCFC12mixingratios.

    @(Courtesy:MaunaLoaObservatory,Hawaii)

    ConsequencesofEnhancedGreenhouseEffect

    i)GlobalWarming

    Increaseofgreenhousegasesconcentrationcausesareductioninoutgoinginfraredradiation,thustheEarth'sclimatemustchangesomehowtorestorethebalancebetweenincomingandoutgoingradiation.ThisclimaticchangewillincludeaglobalwarmingoftheEarth'ssurfaceandtheloweratmosphereaswarmingupisthesimplestwayfortheclimatetogetridoftheextraenergy.However,asmallriseintemperaturewillinducemanyotherchanges,forexample,cloudcoverandwindpatterns.Someofthesechangesmayacttoenhancethewarming(positivefeedbacks),

    otherstocounteractit(negativefeedbacks).

    Usingcomplexclimatemodels,the"IntergovernmentalPanelonClimateChange"intheirthirdassessmentreporthasforecastthatglobalmeansurfacetemperaturewillriseby1.4to5.8bytheendof2100.Thisprojectiontakesintoaccounttheeffectsofaerosolswhichtendtocooltheclimateaswellasthedelayingeffectsoftheoceanswhichhavealargethermalcapacity.However,therearemanyuncertaintiesassociatedwiththisprojectionsuchasfutureemissionratesofgreenhousegases,climatefeedbacks,andthesizeoftheoceandelay...etc.

    ii)SeaLevelRise

    Ifglobalwarmingtakesplace,sealevelwillriseduetotwodifferentprocesses.Firstly,warmertemperaturecausesealeveltoriseduetothethermalexpansionofseawater.Secondly,waterfrommeltingglaciersandtheicesheetsofGreenlandandtheAntarcticawouldalsoaddwatertotheocean.ItispredictedthattheEarth'saveragesealevelwillriseby0.09to0.88m

    between1990and2100.

    PotentialImpactonhumanlife

    a)EconomicImpact

    Overhalfofthehumanpopulationliveswithin100kilometresofthesea.Mostofthispopulationlivesinurbanareasthatserveasseaports.Ameasurableriseinsealevelwillhaveasevereeconomicimpactonlowlyingcoastalareasandislands,forexamples,increasingthebeacherosionratesalongcoastlines,risingsealeveldisplacingfreshgroundwaterforasubstantialdistanceinland.

    b)AgriculturalImpact

    ExperimentshaveshownthatwithhigherconcentrationsofCO2,plantscangrowbiggerandfaster.However,theeffectofglobalwarmingmayaffecttheatmosphericgeneralcirculationandthusalteringtheglobalprecipitationpatternaswellaschangingthesoilmoisturecontentsovervariouscontinents.Sinceitisunclearhowglobalwarmingwillaffectclimateonaregionalorlocalscale,theprobableeffectsonthebiosphereremainsuncertain.

    c)EffectsonAquaticsystems

    Thelossofcoastalwetlandscouldcertainlyreducefishpopulations,especiallyshellfish.Increasedsalinityinestuariescouldreducetheabundanceoffreshwaterspeciesbutcouldincreasethepresenceofmarinespecies.However,thefullimpactonmarinespeciesisnotknown.

    d)EffectsonHydrologicalCycle

    Globalprecipitationislikelytoincrease.However,itisnotknownhowregionalrainfallpatternswillchange.Someregionsmayhavemorerainfall,whileothersmayhaveless.Furthermore,highertemperatureswouldprobablyincreaseevaporation.Thesechangeswouldprobablycreatenewstressesformanywatermanagementsystems.

    Table1Characteristicsofsomemajorgreenhousegases

    Table2GlobalWarmingPotentials(GWPs)followingtheinstantaneousinjectionof1Kgofeach

    Greenhousegas,relativeto1KgofCO2(BasedonIntergovernmentalPanelonClimateChangeThirdAssessmentReport,2001)

    ClimatologicalInformationServices>ClimateChange>GreenHouseEffect

    Greenhousegas Sources Sinks Importanceforclimate

    CarbonDioxide

    (CO2)

    1)Burningoffossilfuel

    2)Landusechange(deforestation)

    1)OceanUptake

    2)Plantsphotosynthesis

    AbsorbsinfraredradiationaffectsstratosphericO3

    Methane

    (CH4)

    1)Biomassburning

    2)Entericfermentation

    3)Ricepaddies

    1)ReactionswithOH

    2)Microorganismsuptakebysoils

    AbsorbsinfraredradiationaffectstroposphericO3andOHaffectsstratosphericO3andH2OproducesCO2

    NitrousOxide

    (N2O)

    1)Biomassburning

    2)Fossilfuelcombustion

    3)Fertilizers

    1)Removalbysoils

    2)StratosphericphotolysisandreactionwithO

    AbsorbsinfraredradiationaffectsstratosphericO3

    Ozone

    (O3)

    PhotochemicalreactionsinvolvingO2

    CatalyticchemicalreactionsinvolvingNOx,ClOxandHOxspecies.

    Absorbsultravioletandinfraredradiation

    CarbonMonoxide

    (CO)

    1)Plantemissions

    2)Manmaderelease(transport,industrial)

    1)Soiluptake

    2)ReactionswithOH

    AffectsstratosphericO3andOHcyclesproducesCO2

    Chlorofluorocarbons

    (CFCs)

    Industrialproduction Insignificantintroposphere,dissociatedinstratosphere(photolysisandreactionwithO)

    AbsorbsinfraredradiationaffectsstratosphericO3

    SulphurDioxide

    (SO2)

    1)Volcanoes

    2)CoalandBiomassburning

    1)Dryandwetdeposition

    2)ReactionswithOH

    Formsaerosols,whichscattersolarradiation

    Greenhousegas EstimatedLifetime

    (years)

    GlobalWarmingPotential

    20years 100years 500years

    CarbonDioxide(CO2) Variable 1 1 1

    Methane(CH4) 12.0 62 23 7

    NitrousOxide(N2O) 114 275 296 156

    Chlorofluorocarbons(CFCs)

    i) CFCl3(CFC11) 45 6300 4600 1600

    ii) CF2Cl2(CFC12) 100 10200 10600 5200

    iii) CClF3(CFC13) 640 10000 14000 16300

    iv) C2F3Cl3(CFC113) 85 6100 6000 2700

    v) C2F4Cl2(CFC114) 300 7500 9800 8700

    vi) C2F5Cl(CFC115) 1700 4900 7200 9900

  • WhatisGreenhouseEffect?

    TheGreenhouseEffectisatermthatreferstoaphysicalpropertyoftheEarth'satmosphere.IftheEarthhadnoatmosphere,itsaveragesurfacetemperaturewouldbeverylowofabout18ratherthanthecomfortable15foundtoday.ThedifferenceintemperatureisduetoasuiteofgasescalledgreenhousegaseswhichaffecttheoverallenergybalanceoftheEarth'ssystembyabsorbinginfraredradiation.Initsexistingstate,theEarthatmospheresystembalancesabsorptionofsolarradiationbyemissionofinfraredradiationtospace(Fig.1).Duetogreenhousegases,theatmosphereabsorbsmoreinfraredenergythan

    itreradiatestospace,resultinginanetwarmingoftheEarthatmospheresystemandofsurfacetemperature.ThisistheNaturalGreenhouseEffect.Withmoregreenhousegasesreleasedtotheatmosphereduetohumanactivity,moreinfraredradiationwillbetrappedintheEarth'ssurfacewhichcontributestotheEnhancedGreenhouseEffect.

    Fig.1Asimplifieddiagramillustratingthegloballongtermradiativebalanceoftheatmosphere.Netinputofsolarradiation(240Wm2)mustbebalancedbynetoutputofinfraredradiation.Aboutathird(103Wm2)ofincomingsolarradiationisreflectedandtheremainderismostlyabsorbedbythesurface.Outgoinginfraredradiationisabsorbedbygreenhousegasesandbycloudskeepingthesurfaceabout33warmerthanitwouldotherwisebe.

    TypesofGreenhousegases

    Greenhousegasescompriselessthan1%oftheatmosphere.Theirlevelsaredeterminedbyabalancebetweensourcesandsinks.Sourcesandsinksareprocessesthatgenerateanddestroygreenhousegasesrespectively.Humanaffectgreenhousegaslevelsbyintroducingnewsourcesorbyinterferingwithnaturalsinks.

    Themajorgreenhousegasesintheatmospherearecarbondioxide(CO2),methane,(CH4),nitrousoxide(N2O),chlorofluorocarbons(CFCs)andozone(O3).Atmosphericwatervapour(H2O)alsomakesalargecontributiontothenaturalgreenhouseeffectbutitisthoughtthatitspresenceisnotdirectlyaffectedbyhumanactivity.CharacteristicsofsomeofthegreenhousegasesareshowninTable1.

    GlobalWarmingPotential(GWP)

    DifferentgreenhousegasesexertdifferenteffectsontheEarth'senergybalance.Inordertoassistpolicymakerstomeasuretheimpactofvariousgreenhousegasesonglobalwarming,theconceptofGlobalWarmingPotentials(GWPs)wasintroducedbytheIntergovernmentalPanelonClimateChange(IPCC)inits1990report.GWPreflectstherelativestrengthofindividualgreenhousegaswithrespecttoitsimpactonglobalwarming.Itwasdefinedasthecumulativeradiativeforcing*betweenthepresentandsomefuturetimecausedbyaunitmassofgreenhousegasemittednow,expressedrelativetoCO2.TheGWPsdevelopedbyIPCCforanumberofgreenhousegasesareshowninTable2.

    GlobalWarmingPotentialstakeintoaccountthedifferingatmosphericlifetimesandabilitiesofvariousgasestoabsorbradiation.DerivationsofGWPsrequiresknowledgeofthefateoftheemittedgas(typicallynotwellunderstood)andtheradiativeforcingduetotheamountremainingintheatmosphere(reasonablywellunderstood).Hence,GWPsencompasscertainuncertainty,typically+35%relativetoCO2reference.

    *Radiativeforcingisdefinedasachangeinaveragenetradiationatthetopofthetroposphere(tropopause)duetoachangeineithersolarorinfraredradiation.Aradiativeforcingperturbsthebalancebetweenincomingandoutgoingradiation.ApositiveradiativeforcingtendsonaveragetowarmtheEarth'ssurfaceanegativeradiativeforcingtendsonaveragetocooltheEarth'ssurface.

    Trendsingreenhousegasconcentrations

    a)CarbonDioxide(CO2)

    HighqualityobservationsoftheconcentrationofCO2beganin1958,withflaskmeasurementsattheMaunaLoaObservatoryinHawaii.Fig.2showsthattheaverageannualconcentrationofCO2intheatmospherehasrisenfromabout315ppmv(partpermillionbyvolume)in1958toaround363ppmvin1997.ThereisaclearannualcycleintheMaunaLoadatathatcorrespondstotheannualcycleofplantrespirationintheNorthernHemisphere:CO2concentrationincreaseduringtheFallandWinteranddeclineduringSpringandSummer.Thiscycle,followsthegrowthanddiebackofvegetation,isreversedandofsmalleramplitudeintheSouthernHemisphere,anddisappearsalmostentirelyinthedatameasuredneartheEquator.

    @Fig.2Atmosphericcarbondioxidemonthlymeanmixingratios.DatapriortoMay1974arefromtheScrippsInstitutionofOceanography(),datasinceMay1974arefromtheU.S.NationalOceanicandAtmosphericAdministration().Alongtermtrendcurve()isfittedtothemonthlymeanvalues.

    b)Methane(CH4)

    Therateofincreaseoftheatmosphericabundanceofmethanehasdeclinedoverthelastdecade,slowingdramaticallyin1991to1992,thoughwithanapparentincreaseinthegrowthrateinlate1993(Fig.3).Theaveragetrendover1980to1990isabout13ppbv/year(partperbillionbyvolume/year).

    @Fig.3AtmosphericmethanemixingratiosfromdiscreteairsamplescollectedatMaunaLoa,Hawaii.Asmoothcurve(red)andlongtermtrend(green)arefittedtothemeasurements(blue).

    c)NitrousOxide(N2O)

    Overthelastfourdecades,theaveragegrowthrateofN2Oisabout0.25%/year(Fig.4).CurrenttroposphericconcentrationofN2Oisaround312to314ppbv.

    @Fig.4AtmosphericN2Omixingratios.

    d)Chlorofluorocarbons(CFCs)

    Amongthefamilycompoundsofchlorocarbons,CFCl3(CFC11)andCF2Cl2(CFC12)arereceivingmoreattentionbecauseoftheirlargerconcentrationsandpotentiallysignificanteffectsonstratosphericozone.CFC11andCFC12havethehighestconcentrationsofthemanmadechlorocarbons,around0.27and0.55ppbv,respectively(measuredatMaunaLoain1997,Fig.5&6).AsindicatedintheirGWPvalues,thesetwogasesarestronginfraredabsorbers.ItisthoughtthatCFC11andCFC12havecontributedaboutonethirdoftheradiativeforcingofgasesotherthanCO2duringthe1980s.

    @Fig.5AtmosphericCFC11mixingratio.

    @Fig.6AtmosphericCFC12mixingratios.

    @(Courtesy:MaunaLoaObservatory,Hawaii)

    ConsequencesofEnhancedGreenhouseEffect

    i)GlobalWarming

    Increaseofgreenhousegasesconcentrationcausesareductioninoutgoinginfraredradiation,thustheEarth'sclimatemustchangesomehowtorestorethebalancebetweenincomingandoutgoingradiation.ThisclimaticchangewillincludeaglobalwarmingoftheEarth'ssurfaceandtheloweratmosphereaswarmingupisthesimplestwayfortheclimatetogetridoftheextraenergy.However,asmallriseintemperaturewillinducemanyotherchanges,forexample,cloudcoverandwindpatterns.Someofthesechangesmayacttoenhancethewarming(positivefeedbacks),

    otherstocounteractit(negativefeedbacks).

    Usingcomplexclimatemodels,the"IntergovernmentalPanelonClimateChange"intheirthirdassessmentreporthasforecastthatglobalmeansurfacetemperaturewillriseby1.4to5.8bytheendof2100.Thisprojectiontakesintoaccounttheeffectsofaerosolswhichtendtocooltheclimateaswellasthedelayingeffectsoftheoceanswhichhavealargethermalcapacity.However,therearemanyuncertaintiesassociatedwiththisprojectionsuchasfutureemissionratesofgreenhousegases,climatefeedbacks,andthesizeoftheoceandelay...etc.

    ii)SeaLevelRise

    Ifglobalwarmingtakesplace,sealevelwillriseduetotwodifferentprocesses.Firstly,warmertemperaturecausesealeveltoriseduetothethermalexpansionofseawater.Secondly,waterfrommeltingglaciersandtheicesheetsofGreenlandandtheAntarcticawouldalsoaddwatertotheocean.ItispredictedthattheEarth'saveragesealevelwillriseby0.09to0.88m

    between1990and2100.

    PotentialImpactonhumanlife

    a)EconomicImpact

    Overhalfofthehumanpopulationliveswithin100kilometresofthesea.Mostofthispopulationlivesinurbanareasthatserveasseaports.Ameasurableriseinsealevelwillhaveasevereeconomicimpactonlowlyingcoastalareasandislands,forexamples,increasingthebeacherosionratesalongcoastlines,risingsealeveldisplacingfreshgroundwaterforasubstantialdistanceinland.

    b)AgriculturalImpact

    ExperimentshaveshownthatwithhigherconcentrationsofCO2,plantscangrowbiggerandfaster.However,theeffectofglobalwarmingmayaffecttheatmosphericgeneralcirculationandthusalteringtheglobalprecipitationpatternaswellaschangingthesoilmoisturecontentsovervariouscontinents.Sinceitisunclearhowglobalwarmingwillaffectclimateonaregionalorlocalscale,theprobableeffectsonthebiosphereremainsuncertain.

    c)EffectsonAquaticsystems

    Thelossofcoastalwetlandscouldcertainlyreducefishpopulations,especiallyshellfish.Increasedsalinityinestuariescouldreducetheabundanceoffreshwaterspeciesbutcouldincreasethepresenceofmarinespecies.However,thefullimpactonmarinespeciesisnotknown.

    d)EffectsonHydrologicalCycle

    Globalprecipitationislikelytoincrease.However,itisnotknownhowregionalrainfallpatternswillchange.Someregionsmayhavemorerainfall,whileothersmayhaveless.Furthermore,highertemperatureswouldprobablyincreaseevaporation.Thesechangeswouldprobablycreatenewstressesformanywatermanagementsystems.

    Table1Characteristicsofsomemajorgreenhousegases

    Table2GlobalWarmingPotentials(GWPs)followingtheinstantaneousinjectionof1Kgofeach

    Greenhousegas,relativeto1KgofCO2(BasedonIntergovernmentalPanelonClimateChangeThirdAssessmentReport,2001)

    ClimatologicalInformationServices>ClimateChange>GreenHouseEffect

    Greenhousegas Sources Sinks Importanceforclimate

    CarbonDioxide

    (CO2)

    1)Burningoffossilfuel

    2)Landusechange(deforestation)

    1)OceanUptake

    2)Plantsphotosynthesis

    AbsorbsinfraredradiationaffectsstratosphericO3

    Methane

    (CH4)

    1)Biomassburning

    2)Entericfermentation

    3)Ricepaddies

    1)ReactionswithOH

    2)Microorganismsuptakebysoils

    AbsorbsinfraredradiationaffectstroposphericO3andOHaffectsstratosphericO3andH2OproducesCO2

    NitrousOxide

    (N2O)

    1)Biomassburning

    2)Fossilfuelcombustion

    3)Fertilizers

    1)Removalbysoils

    2)StratosphericphotolysisandreactionwithO

    AbsorbsinfraredradiationaffectsstratosphericO3

    Ozone

    (O3)

    PhotochemicalreactionsinvolvingO2

    CatalyticchemicalreactionsinvolvingNOx,ClOxandHOxspecies.

    Absorbsultravioletandinfraredradiation

    CarbonMonoxide

    (CO)

    1)Plantemissions

    2)Manmaderelease(transport,industrial)

    1)Soiluptake

    2)ReactionswithOH

    AffectsstratosphericO3andOHcyclesproducesCO2

    Chlorofluorocarbons

    (CFCs)

    Industrialproduction Insignificantintroposphere,dissociatedinstratosphere(photolysisandreactionwithO)

    AbsorbsinfraredradiationaffectsstratosphericO3

    SulphurDioxide

    (SO2)

    1)Volcanoes

    2)CoalandBiomassburning

    1)Dryandwetdeposition

    2)ReactionswithOH

    Formsaerosols,whichscattersolarradiation

    Greenhousegas EstimatedLifetime

    (years)

    GlobalWarmingPotential

    20years 100years 500years

    CarbonDioxide(CO2) Variable 1 1 1

    Methane(CH4) 12.0 62 23 7

    NitrousOxide(N2O) 114 275 296 156

    Chlorofluorocarbons(CFCs)

    i) CFCl3(CFC11) 45 6300 4600 1600

    ii) CF2Cl2(CFC12) 100 10200 10600 5200

    iii) CClF3(CFC13) 640 10000 14000 16300

    iv) C2F3Cl3(CFC113) 85 6100 6000 2700

    v) C2F4Cl2(CFC114) 300 7500 9800 8700

    vi) C2F5Cl(CFC115) 1700 4900 7200 9900

  • WhatisGreenhouseEffect?

    TheGreenhouseEffectisatermthatreferstoaphysicalpropertyoftheEarth'satmosphere.IftheEarthhadnoatmosphere,itsaveragesurfacetemperaturewouldbeverylowofabout18ratherthanthecomfortable15foundtoday.ThedifferenceintemperatureisduetoasuiteofgasescalledgreenhousegaseswhichaffecttheoverallenergybalanceoftheEarth'ssystembyabsorbinginfraredradiation.Initsexistingstate,theEarthatmospheresystembalancesabsorptionofsolarradiationbyemissionofinfraredradiationtospace(Fig.1).Duetogreenhousegases,theatmosphereabsorbsmoreinfraredenergythan

    itreradiatestospace,resultinginanetwarmingoftheEarthatmospheresystemandofsurfacetemperature.ThisistheNaturalGreenhouseEffect.Withmoregreenhousegasesreleasedtotheatmosphereduetohumanactivity,moreinfraredradiationwillbetrappedintheEarth'ssurfacewhichcontributestotheEnhancedGreenhouseEffect.

    Fig.1Asimplifieddiagramillustratingthegloballongtermradiativebalanceoftheatmosphere.Netinputofsolarradiation(240Wm2)mustbebalancedbynetoutputofinfraredradiation.Aboutathird(103Wm2)ofincomingsolarradiationisreflectedandtheremainderismostlyabsorbedbythesurface.Outgoinginfraredradiationisabsorbedbygreenhousegasesandbycloudskeepingthesurfaceabout33warmerthanitwouldotherwisebe.

    TypesofGreenhousegases

    Greenhousegasescompriselessthan1%oftheatmosphere.Theirlevelsaredeterminedbyabalancebetweensourcesandsinks.Sourcesandsinksareprocessesthatgenerateanddestroygreenhousegasesrespectively.Humanaffectgreenhousegaslevelsbyintroducingnewsourcesorbyinterferingwithnaturalsinks.

    Themajorgreenhousegasesintheatmospherearecarbondioxide(CO2),methane,(CH4),nitrousoxide(N2O),chlorofluorocarbons(CFCs)andozone(O3).Atmosphericwatervapour(H2O)alsomakesalargecontributiontothenaturalgreenhouseeffectbutitisthoughtthatitspresenceisnotdirectlyaffectedbyhumanactivity.CharacteristicsofsomeofthegreenhousegasesareshowninTable1.

    GlobalWarmingPotential(GWP)

    DifferentgreenhousegasesexertdifferenteffectsontheEarth'senergybalance.Inordertoassistpolicymakerstomeasuretheimpactofvariousgreenhousegasesonglobalwarming,theconceptofGlobalWarmingPotentials(GWPs)wasintroducedbytheIntergovernmentalPanelonClimateChange(IPCC)inits1990report.GWPreflectstherelativestrengthofindividualgreenhousegaswithrespecttoitsimpactonglobalwarming.Itwasdefinedasthecumulativeradiativeforcing*betweenthepresentandsomefuturetimecausedbyaunitmassofgreenhousegasemittednow,expressedrelativetoCO2.TheGWPsdevelopedbyIPCCforanumberofgreenhousegasesareshowninTable2.

    GlobalWarmingPotentialstakeintoaccountthedifferingatmosphericlifetimesandabilitiesofvariousgasestoabsorbradiation.DerivationsofGWPsrequiresknowledgeofthefateoftheemittedgas(typicallynotwellunderstood)andtheradiativeforcingduetotheamountremainingintheatmosphere(reasonablywellunderstood).Hence,GWPsencompasscertainuncertainty,typically+35%relativetoCO2reference.

    *Radiativeforcingisdefinedasachangeinaveragenetradiationatthetopofthetroposphere(tropopause)duetoachangeineithersolarorinfraredradiation.Aradiativeforcingperturbsthebalancebetweenincomingandoutgoingradiation.ApositiveradiativeforcingtendsonaveragetowarmtheEarth'ssurfaceanegativeradiativeforcingtendsonaveragetocooltheEarth'ssurface.

    Trendsingreenhousegasconcentrations

    a)CarbonDioxide(CO2)

    HighqualityobservationsoftheconcentrationofCO2beganin1958,withflaskmeasurementsattheMaunaLoaObservatoryinHawaii.Fig.2showsthattheaverageannualconcentrationofCO2intheatmospherehasrisenfromabout315ppmv(partpermillionbyvolume)in1958toaround363ppmvin1997.ThereisaclearannualcycleintheMaunaLoadatathatcorrespondstotheannualcycleofplantrespirationintheNorthernHemisphere:CO2concentrationincreaseduringtheFallandWinteranddeclineduringSpringandSummer.Thiscycle,followsthegrowthanddiebackofvegetation,isreversedandofsmalleramplitudeintheSouthernHemisphere,anddisappearsalmostentirelyinthedatameasuredneartheEquator.

    @Fig.2Atmosphericcarbondioxidemonthlymeanmixingratios.DatapriortoMay1974arefromtheScrippsInstitutionofOceanography(),datasinceMay1974arefromtheU.S.NationalOceanicandAtmosphericAdministration().Alongtermtrendcurve()isfittedtothemonthlymeanvalues.

    b)Methane(CH4)

    Therateofincreaseoftheatmosphericabundanceofmethanehasdeclinedoverthelastdecade,slowingdramaticallyin1991to1992,thoughwithanapparentincreaseinthegrowthrateinlate1993(Fig.3).Theaveragetrendover1980to1990isabout13ppbv/year(partperbillionbyvolume/year).

    @Fig.3AtmosphericmethanemixingratiosfromdiscreteairsamplescollectedatMaunaLoa,Hawaii.Asmoothcurve(red)andlongtermtrend(green)arefittedtothemeasurements(blue).

    c)NitrousOxide(N2O)

    Overthelastfourdecades,theaveragegrowthrateofN2Oisabout0.25%/year(Fig.4).CurrenttroposphericconcentrationofN2Oisaround312to314ppbv.

    @Fig.4AtmosphericN2Omixingratios.

    d)Chlorofluorocarbons(CFCs)

    Amongthefamilycompoundsofchlorocarbons,CFCl3(CFC11)andCF2Cl2(CFC12)arereceivingmoreattentionbecauseoftheirlargerconcentrationsandpotentiallysignificanteffectsonstratosphericozone.CFC11andCFC12havethehighestconcentrationsofthemanmadechlorocarbons,around0.27and0.55ppbv,respectively(measuredatMaunaLoain1997,Fig.5&6).AsindicatedintheirGWPvalues,thesetwogasesarestronginfraredabsorbers.ItisthoughtthatCFC11andCFC12havecontributedaboutonethirdoftheradiativeforcingofgasesotherthanCO2duringthe1980s.

    @Fig.5AtmosphericCFC11mixingratio.

    @Fig.6AtmosphericCFC12mixingratios.

    @(Courtesy:MaunaLoaObservatory,Hawaii)

    ConsequencesofEnhancedGreenhouseEffect

    i)GlobalWarming

    Increaseofgreenhousegasesconcentrationcausesareductioninoutgoinginfraredradiation,thustheEarth'sclimatemustchangesomehowtorestorethebalancebetweenincomingandoutgoingradiation.ThisclimaticchangewillincludeaglobalwarmingoftheEarth'ssurfaceandtheloweratmosphereaswarmingupisthesimplestwayfortheclimatetogetridoftheextraenergy.However,asmallriseintemperaturewillinducemanyotherchanges,forexample,cloudcoverandwindpatterns.Someofthesechangesmayacttoenhancethewarming(positivefeedbacks),

    otherstocounteractit(negativefeedbacks).

    Usingcomplexclimatemodels,the"IntergovernmentalPanelonClimateChange"intheirthirdassessmentreporthasforecastthatglobalmeansurfacetemperaturewillriseby1.4to5.8bytheendof2100.Thisprojectiontakesintoaccounttheeffectsofaerosolswhichtendtocooltheclimateaswellasthedelayingeffectsoftheoceanswhichhavealargethermalcapacity.However,therearemanyuncertaintiesassociatedwiththisprojectionsuchasfutureemissionratesofgreenhousegases,climatefeedbacks,andthesizeoftheoceandelay...etc.

    ii)SeaLevelRise

    Ifglobalwarmingtakesplace,sealevelwillriseduetotwodifferentprocesses.Firstly,warmertemperaturecausesealeveltoriseduetothethermalexpansionofseawater.Secondly,waterfrommeltingglaciersandtheicesheetsofGreenlandandtheAntarcticawouldalsoaddwatertotheocean.ItispredictedthattheEarth'saveragesealevelwillriseby0.09to0.88m

    between1990and2100.

    PotentialImpactonhumanlife

    a)EconomicImpact

    Overhalfofthehumanpopulationliveswithin100kilometresofthesea.Mostofthispopulationlivesinurbanareasthatserveasseaports.Ameasurableriseinsealevelwillhaveasevereeconomicimpactonlowlyingcoastalareasandislands,forexamples,increasingthebeacherosionratesalongcoastlines,risingsealeveldisplacingfreshgroundwaterforasubstantialdistanceinland.

    b)AgriculturalImpact

    ExperimentshaveshownthatwithhigherconcentrationsofCO2,plantscangrowbiggerandfaster.However,theeffectofglobalwarmingmayaffecttheatmosphericgeneralcirculationandthusalteringtheglobalprecipitationpatternaswellaschangingthesoilmoisturecontentsovervariouscontinents.Sinceitisunclearhowglobalwarmingwillaffectclimateonaregionalorlocalscale,theprobableeffectsonthebiosphereremainsuncertain.

    c)EffectsonAquaticsystems

    Thelossofcoastalwetlandscouldcertainlyreducefishpopulations,especiallyshellfish.Increasedsalinityinestuariescouldreducetheabundanceoffreshwaterspeciesbutcouldincreasethepresenceofmarinespecies.However,thefullimpactonmarinespeciesisnotknown.

    d)EffectsonHydrologicalCycle

    Globalprecipitationislikelytoincrease.However,itisnotknownhowregionalrainfallpatternswillchange.Someregionsmayhavemorerainfall,whileothersmayhaveless.Furthermore,highertemperatureswouldprobablyincreaseevaporation.Thesechangeswouldprobablycreatenewstressesformanywatermanagementsystems.

    Table1Characteristicsofsomemajorgreenhousegases

    Table2GlobalWarmingPotentials(GWPs)followingtheinstantaneousinjectionof1Kgofeach

    Greenhousegas,relativeto1KgofCO2(BasedonIntergovernmentalPanelonClimateChangeThirdAssessmentReport,2001)

    ClimatologicalInformationServices>ClimateChange>GreenHouseEffect

    Greenhousegas Sources Sinks Importanceforclimate

    CarbonDioxide

    (CO2)

    1)Burningoffossilfuel

    2)Landusechange(deforestation)

    1)OceanUptake

    2)Plantsphotosynthesis

    AbsorbsinfraredradiationaffectsstratosphericO3

    Methane

    (CH4)

    1)Biomassburning

    2)Entericfermentation

    3)Ricepaddies

    1)ReactionswithOH

    2)Microorganismsuptakebysoils

    AbsorbsinfraredradiationaffectstroposphericO3andOHaffectsstratosphericO3andH2OproducesCO2

    NitrousOxide

    (N2O)

    1)Biomassburning

    2)Fossilfuelcombustion

    3)Fertilizers

    1)Removalbysoils

    2)StratosphericphotolysisandreactionwithO

    AbsorbsinfraredradiationaffectsstratosphericO3

    Ozone

    (O3)

    PhotochemicalreactionsinvolvingO2

    CatalyticchemicalreactionsinvolvingNOx,ClOxandHOxspecies.

    Absorbsultravioletandinfraredradiation

    CarbonMonoxide

    (CO)

    1)Plantemissions

    2)Manmaderelease(transport,industrial)

    1)Soiluptake

    2)ReactionswithOH

    AffectsstratosphericO3andOHcyclesproducesCO2

    Chlorofluorocarbons

    (CFCs)

    Industrialproduction Insignificantintroposphere,dissociatedinstratosphere(photolysisandreactionwithO)

    AbsorbsinfraredradiationaffectsstratosphericO3

    SulphurDioxide

    (SO2)

    1)Volcanoes

    2)CoalandBiomassburning

    1)Dryandwetdeposition

    2)ReactionswithOH

    Formsaerosols,whichscattersolarradiation

    Greenhousegas EstimatedLifetime

    (years)

    GlobalWarmingPotential

    20years 100years 500years

    CarbonDioxide(CO2) Variable 1 1 1

    Methane(CH4) 12.0 62 23 7

    NitrousOxide(N2O) 114 275 296 156

    Chlorofluorocarbons(CFCs)

    i) CFCl3(CFC11) 45 6300 4600 1600

    ii) CF2Cl2(CFC12) 100 10200 10600 5200

    iii) CClF3(CFC13) 640 10000 14000 16300

    iv) C2F3Cl3(CFC113) 85 6100 6000 2700

    v) C2F4Cl2(CFC114) 300 7500 9800 8700

    vi) C2F5Cl(CFC115) 1700 4900 7200 9900

  • WhatisGreenhouseEffect?

    TheGreenhouseEffectisatermthatreferstoaphysicalpropertyoftheEarth'satmosphere.IftheEarthhadnoatmosphere,itsaveragesurfacetemperaturewouldbeverylowofabout18ratherthanthecomfortable15foundtoday.ThedifferenceintemperatureisduetoasuiteofgasescalledgreenhousegaseswhichaffecttheoverallenergybalanceoftheEarth'ssystembyabsorbinginfraredradiation.Initsexistingstate,theEarthatmospheresystembalancesabsorptionofsolarradiationbyemissionofinfraredradiationtospace(Fig.1).Duetogreenhousegases,theatmosphereabsorbsmoreinfraredenergythan

    itreradiatestospace,resultinginanetwarmingoftheEarthatmospheresystemandofsurfacetemperature.ThisistheNaturalGreenhouseEffect.Withmoregreenhousegasesreleasedtotheatmosphereduetohumanactivity,moreinfraredradiationwillbetrappedintheEarth'ssurfacewhichcontributestotheEnhancedGreenhouseEffect.

    Fig.1Asimplifieddiagramillustratingthegloballongtermradiativebalanceoftheatmosphere.Netinputofsolarradiation(240Wm2)mustbebalancedbynetoutputofinfraredradiation.Aboutathird(103Wm2)ofincomingsolarradiationisreflectedandtheremainderismostlyabsorbedbythesurface.Outgoinginfraredradiationisabsorbedbygreenhousegasesandbycloudskeepingthesurfaceabout33warmerthanitwouldotherwisebe.

    TypesofGreenhousegases

    Greenhousegasescompriselessthan1%oftheatmosphere.Theirlevelsaredeterminedbyabalancebetweensourcesandsinks.Sourcesandsinksareprocessesthatgenerateanddestroygreenhousegasesrespectively.Humanaffectgreenhousegaslevelsbyintroducingnewsourcesorbyinterferingwithnaturalsinks.

    Themajorgreenhousegasesintheatmospherearecarbondioxide(CO2),methane,(CH4),nitrousoxide(N2O),chlorofluorocarbons(CFCs)andozone(O3).Atmosphericwatervapour(H2O)alsomakesalargecontributiontothenaturalgreenhouseeffectbutitisthoughtthatitspresenceisnotdirectlyaffectedbyhumanactivity.CharacteristicsofsomeofthegreenhousegasesareshowninTable1.

    GlobalWarmingPotential(GWP)

    DifferentgreenhousegasesexertdifferenteffectsontheEarth'senergybalance.Inordertoassistpolicymakerstomeasuretheimpactofvariousgreenhousegasesonglobalwarming,theconceptofGlobalWarmingPotentials(GWPs)wasintroducedbytheIntergovernmentalPanelonClimateChange(IPCC)inits1990report.GWPreflectstherelativestrengthofindividualgreenhousegaswithrespecttoitsimpactonglobalwarming.Itwasdefinedasthecumulativeradiativeforcing*betweenthepresentandsomefuturetimecausedbyaunitmassofgreenhousegasemittednow,expressedrelativetoCO2.TheGWPsdevelopedbyIPCCforanumberofgreenhousegasesareshowninTable2.

    GlobalWarmingPotentialstakeintoaccountthedifferingatmosphericlifetimesandabilitiesofvariousgasestoabsorbradiation.DerivationsofGWPsrequiresknowledgeofthefateoftheemittedgas(typicallynotwellunderstood)andtheradiativeforcingduetotheamountremainingintheatmosphere(reasonablywellunderstood).Hence,GWPsencompasscertainuncertainty,typically+35%relativetoCO2reference.

    *Radiativeforcingisdefinedasachangeinaveragenetradiationatthetopofthetroposphere(tropopause)duetoachangeineithersolarorinfraredradiation.Aradiativeforcingperturbsthebalancebetweenincomingandoutgoingradiation.ApositiveradiativeforcingtendsonaveragetowarmtheEarth'ssurfaceanegativeradiativeforcingtendsonaveragetocooltheEarth'ssurface.

    Trendsingreenhousegasconcentrations

    a)CarbonDioxide(CO2)

    HighqualityobservationsoftheconcentrationofCO2beganin1958,withflaskmeasurementsattheMaunaLoaObservatoryinHawaii.Fig.2showsthattheaverageannualconcentrationofCO2intheatmospherehasrisenfromabout315ppmv(partpermillionbyvolume)in1958toaround363ppmvin1997.ThereisaclearannualcycleintheMaunaLoadatathatcorrespondstotheannualcycleofplantrespirationintheNorthernHemisphere:CO2concentrationincreaseduringtheFallandWinteranddeclineduringSpringandSummer.Thiscycle,followsthegrowthanddiebackofvegetation,isreversedandofsmalleramplitudeintheSouthernHemisphere,anddisappearsalmostentirelyinthedatameasuredneartheEquator.

    @Fig.2Atmosphericcarbondioxidemonthlymeanmixingratios.DatapriortoMay1974arefromtheScrippsInstitutionofOceanography(),datasinceMay1974arefromtheU.S.NationalOceanicandAtmosphericAdministration().Alongtermtrendcurve()isfittedtothemonthlymeanvalues.

    b)Methane(CH4)

    Therateofincreaseoftheatmosphericabundanceofmethanehasdeclinedoverthelastdecade,slowingdramaticallyin1991to1992,thoughwithanapparentincreaseinthegrowthrateinlate1993(Fig.3).Theaveragetrendover1980to1990isabout13ppbv/year(partperbillionbyvolume/year).

    @Fig.3AtmosphericmethanemixingratiosfromdiscreteairsamplescollectedatMaunaLoa,Hawaii.Asmoothcurve(red)andlongtermtrend(green)arefittedtothemeasurements(blue).

    c)NitrousOxide(N2O)

    Overthelastfourdecades,theaveragegrowthrateofN2Oisabout0.25%/year(Fig.4).CurrenttroposphericconcentrationofN2Oisaround312to314ppbv.

    @Fig.4AtmosphericN2Omixingratios.

    d)Chlorofluorocarbons(CFCs)

    Amongthefamilycompoundsofchlorocarbons,CFCl3(CFC11)andCF2Cl2(CFC12)arereceivingmoreattentionbecauseoftheirlargerconcentrationsandpotentiallysignificanteffectsonstratosphericozone.CFC11andCFC12havethehighestconcentrationsofthemanmadechlorocarbons,around0.27and0.55ppbv,respectively(measuredatMaunaLoain1997,Fig.5&6).AsindicatedintheirGWPvalues,thesetwogasesarestronginfraredabsorbers.ItisthoughtthatCFC11andCFC12havecontributedaboutonethirdoftheradiativeforcingofgasesotherthanCO2duringthe1980s.

    @Fig.5AtmosphericCFC11mixingratio.

    @Fig.6AtmosphericCFC12mixingratios.

    @(Courtesy:MaunaLoaObservatory,Hawaii)

    ConsequencesofEnhancedGreenhouseEffect

    i)GlobalWarming

    Increaseofgreenhousegasesconcentrationcausesareductioninoutgoinginfraredradiation,thustheEarth'sclimatemustchangesomehowtorestorethebalancebetweenincomingandoutgoingradiation.ThisclimaticchangewillincludeaglobalwarmingoftheEarth'ssurfaceandtheloweratmosphereaswarmingupisthesimplestwayfortheclimatetogetridoftheextraenergy.However,asmallriseintemperaturewillinducemanyotherchanges,forexample,cloudcoverandwindpatterns.Someofthesechangesmayacttoenhancethewarming(positivefeedbacks),

    otherstocounteractit(negativefeedbacks).

    Usingcomplexclimatemodels,the"IntergovernmentalPanelonClimateChange"intheirthirdassessmentreporthasforecastthatglobalmeansurfacetemperaturewillriseby1.4to5.8bytheendof2100.Thisprojectiontakesintoaccounttheeffectsofaerosolswhichtendtocooltheclimateaswellasthedelayingeffectsoftheoceanswhichhavealargethermalcapacity.However,therearemanyuncertaintiesassociatedwiththisprojectionsuchasfutureemissionratesofgreenhousegases,climatefeedbacks,andthesizeoftheoceandelay...etc.

    ii)SeaLevelRise

    Ifglobalwarmingtakesplace,sealevelwillriseduetotwodifferentprocesses.Firstly,warmertemperaturecausesealeveltoriseduetothethermalexpansionofseawater.Secondly,waterfrommeltingglaciersandtheicesheetsofGreenlandandtheAntarcticawouldalsoaddwatertotheocean.ItispredictedthattheEarth'saveragesealevelwillriseby0.09to0.88m

    between1990and2100.

    PotentialImpactonhumanlife

    a)EconomicImpact

    Overhalfofthehumanpopulationliveswithin100kilometresofthesea.Mostofthispopulationlivesinurbanareasthatserveasseaports.Ameasurableriseinsealevelwillhaveasevereeconomicimpactonlowlyingcoastalareasandislands,forexamples,increasingthebeacherosionratesalongcoastlines,risingsealeveldisplacingfreshgroundwaterforasubstantialdistanceinland.

    b)AgriculturalImpact

    ExperimentshaveshownthatwithhigherconcentrationsofCO2,plantscangrowbiggerandfaster.However,theeffectofglobalwarmingmayaffecttheatmosphericgeneralcirculationandthusalteringtheglobalprecipitationpatternaswellaschangingthesoilmoisturecontentsovervariouscontinents.Sinceitisunclearhowglobalwarmingwillaffectclimateonaregionalorlocalscale,theprobableeffectsonthebiosphereremainsuncertain.

    c)EffectsonAquaticsystems

    Thelossofcoastalwetlandscouldcertainlyreducefishpopulations,especiallyshellfish.Increasedsalinityinestuariescouldreducetheabundanceoffreshwaterspeciesbutcouldincreasethepresenceofmarinespecies.However,thefullimpactonmarinespeciesisnotknown.

    d)EffectsonHydrologicalCycle

    Globalprecipitationislikelytoincrease.However,itisnotknownhowregionalrainfallpatternswillchange.Someregionsmayhavemorerainfall,whileothersmayhaveless.Furthermore,highertemperatureswouldprobablyincreaseevaporation.Thesechangeswouldprobablycreatenewstressesformanywatermanagementsystems.

    Table1Characteristicsofsomemajorgreenhousegases

    Table2GlobalWarmingPotentials(GWPs)followingtheinstantaneousinjectionof1Kgofeach

    Greenhousegas,relativeto1KgofCO2(BasedonIntergovernmentalPanelonClimateChangeThirdAssessmentReport,2001)

    ClimatologicalInformationServices>ClimateChange>GreenHouseEffect

    Greenhousegas Sources Sinks Importanceforclimate

    CarbonDioxide

    (CO2)

    1)Burningoffossilfuel

    2)Landusechange(deforestation)

    1)OceanUptake

    2)Plantsphotosynthesis

    AbsorbsinfraredradiationaffectsstratosphericO3

    Methane

    (CH4)

    1)Biomassburning

    2)Entericfermentation

    3)Ricepaddies

    1)ReactionswithOH

    2)Microorganismsuptakebysoils

    AbsorbsinfraredradiationaffectstroposphericO3andOHaffectsstratosphericO3andH2OproducesCO2

    NitrousOxide

    (N2O)

    1)Biomassburning

    2)Fossilfuelcombustion

    3)Fertilizers

    1)Removalbysoils

    2)StratosphericphotolysisandreactionwithO

    AbsorbsinfraredradiationaffectsstratosphericO3

    Ozone

    (O3)

    PhotochemicalreactionsinvolvingO2

    CatalyticchemicalreactionsinvolvingNOx,ClOxandHOxspecies.

    Absorbsultravioletandinfraredradiation

    CarbonMonoxide

    (CO)

    1)Plantemissions

    2)Manmaderelease(transport,industrial)

    1)Soiluptake

    2)ReactionswithOH

    AffectsstratosphericO3andOHcyclesproducesCO2

    Chlorofluorocarbons

    (CFCs)

    Industrialproduction Insignificantintroposphere,dissociatedinstratosphere(photolysisandreactionwithO)

    AbsorbsinfraredradiationaffectsstratosphericO3

    SulphurDioxide

    (SO2)

    1)Volcanoes

    2)CoalandBiomassburning

    1)Dryandwetdeposition

    2)ReactionswithOH

    Formsaerosols,whichscattersolarradiation

    Greenhousegas EstimatedLifetime

    (years)

    GlobalWarmingPotential

    20years 100years 500years

    CarbonDioxide(CO2) Variable 1 1 1

    Methane(CH4) 12.0 62 23 7

    NitrousOxide(N2O) 114 275 296 156

    Chlorofluorocarbons(CFCs)

    i) CFCl3(CFC11) 45 6300 4600 1600

    ii) CF2Cl2(CFC12) 100 10200 10600 5200

    iii) CClF3(CFC13) 640 10000 14000 16300

    iv) C2F3Cl3(CFC113) 85 6100 6000 2700

    v) C2F4Cl2(CFC114) 300 7500 9800 8700

    vi) C2F5Cl(CFC115) 1700 4900 7200 9900


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Daniel Zanella and Alexander Weygers

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Effective Parenting: Establishing Boundaries

Chapter 23

Chapter-01

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The Best American Humorous Short Stories

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One Flew Over the Cuckoo's Nest

Explore The Levels of Creation

The Last Carnival I Ever Saw

Personality Development

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Star Wars Original Trilogy Trivia (Episodes IV-VI)

Basic Buffer Overflows Explained

Steve Jobs' Commencement Speech at Stanford

Iron Mills Essay

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