PHYS-E0582SpecialCourseinAdvancedEnergyTechnologies-BasicsofClimate
Change,autumn2015
Exercise219.11.2015
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€
1.CalculatetheequilibriumtemperatureforEarthwithoutanyatmosphere.
AssumeEarthasablackbodyandpartiallycoveredwithclouds,sothatEarth’s
planetaryalbedois0.35.IfthecloudscoverhalfoftheEarth’ssurface(when
albedois0.35)andnowtheirreflectivityincreasesby1%,whatchangethis
makestotheEarth’sequilibriumtemperature?
Earth’sequilibriumtemperature(Teq)isgivenby(Stefan-Boltzmannlaw):
S (1 − α Earth )
S0 (1 − α Earth )
Teq4 = 0
⇒ Teq =
Eq:1
4σ
4σ
Where:So=1361W/m2,σ=5.6710-8W(m2K4)(Stefan-Boltzmann’sconstant)
Whenearth’splanetaryalbedois0.35,equilibriumtemperature(Teq)isgivenby:
W
221.16 2 4
mK
Teq =
≈ 249.909K ≈ (249.909 − 273.15)°C ≈ −23.2°C W
−8
5.67 × 10
m 2K 4
Assumethatclouds’reflectivityincreaseby1%willincreasethetotalalbedoby1%
(eventhoughitwillbeabitless,becauseonlyabout½ofEarthiscoveredwith
clouds).
Newalbedowillbe:0.35*1.01=0.3535
WhenEarth’splanetaryalbedois0.3535,equilibriumtemperature(Teq)isgivenby:
W
m 2K 4 ≈ 249.572 K ≈ (249.572 − 273.15)°C ≈ −23.6°C Teq =
W
5.67 × 10 −8 2 4
mK
219.971
€ TheEarth’sequilibriumtemperaturedecreasesby0.4degrees.
2.
a)Explainwhathappenswhenamoleculeabsorbsaphoton(=quantumof
electromagneticradiation)atacertainwavelength?
Dependingonthephotonenergyandthenatureofmolecule,absorptionofphoton
mayresultinexcitementofthemolecule(electronmovestoahigherenergylevel)or
maycauseincreaseinvibrationalandrotationalmotionofthemolecularstructure.
Whentheexcitedstaterelaxes,electronmovestotheoriginallowerstate,emitting
thephotonofthesamewavelengththatwasabsorbed.
b)NameatleasttwomostimportantabsorptionbandsforEarth’sinfrared
radiationinthefigurebelow.
c)WhatisthemostimportantgreenhousegasintheEarth’satmosphereand
why?
WatervaporisthemostimportantGHGwhichcontributestoabout60%ofthe
greenhouseeffect.Thisisbecause1)ithasverywideabsorptionband(absorbsin
manywavelengths)and2)itsconcentrationishighintheatmosphere,about0,5%.
d)Whatdoesitmeanwhen“absorptionbandissaturated”?Doestheband
saturationeffectpreventglobalwarmingfromCO2?
Whenthepeakofabsorptiondoesnotchangeonincreaseintheconcentrationofthe
gas,wecallitsaturated.However,itdoesnotpreventglobalwarmingastheband
startsbroadeningonthebothsidesofabsorptionband(therearestillpossible
absorptionenergylevelsattheendsofabsorptionband)increaseofCO2gas
concentration.
3.ComparetheclimateresponsetoincreasedCO2andCH4.Usethemodel
Slugulatorathttp://climatemodels.uchicago.edu/slugulator/
a)PutaCO2spikeemissionof1000Gt.Howmuchwarmingwillthis
causeandwhen?Whenthetemperaturestartstodeclineagain?
Thiswouldcause~3degreeswarminginsurfacetemperatureanomaly*duringfirst
~50years.Afterthattemperaturestartsdeclining.
b)PutnowaCH4spikeemissionof50Gt.Howmuchwarmingwill
thiscauseandwhen?
Thiswouldcause~2degreeswarminginsurfacetemperatureanomalyduringfirst
~12years.Afterthattemperaturestartsdeclining.
c)Howtheradiativeforcingcurveslooklikeinthesecases?
WiththeCO2spike,theradiativeforcingimmediatelyincreasesby~6W/m2and
veryslowlystartstodecrease.Withthemethanespike,theradiativeforcing
immediatelyincreasesby6W/m2,andthenalmostlinearlydecreasesbacktonormal
inabout40years.
Whatisthereasonforthedifferentresponsesforthesegases?
Thereasonfordifferentresponses(intimespan)isbecauseofsignificantdifference
intheirlifetimes:CO2about200years,CH412years.Also,methaneismoreefficient
inabsorbinginfraredradiationper1Gtemission,whichisseenthattheybothcause
initiallythesameradiativeforcing(6W/m2),eventhoughmethaneamountismuch
smaller.
*Temperatureanomaly=differenceintemperaturerelativetosomereferencetime
4.Dynamicstructureoftheatmosphereandworldoceanleadstoawiderange
ofcharacteristictimesformixing(i.e.transferofmatterbetweentwo
locations)andresidencetimesofdifferentspecies.Pleasefindthemissing
valuesandfillinthetablebelow.
planetaryboundarylayer–freetroposphere
intrahemispheric(introposphere)east-west
interhemispheric(introposphere)northsouth
troposphere–stratosphere
surfaceocean–deepocean
Introposphere
CO2
O 3
CH4
N2O
SF6
aerosolparticles
Instratosphere
N2O
O 3
CH4
CFCs
aerosolparticles
Mixingtimes
onemonth
fewweeks
1year
3years
>100years,upto1000years*
Residencetimes/half-lives
100-300years
hours–10days**
Uppertroposphere100-200days
12years***
120years
3200years
days–fewweeks
120years
uptosomemonths**(variable)
195years****
45-10000years(dependsonthe
compound)*****
1-2years
Typicallylifetimesinstratospherearelongerthanintroposphere.
Forgasesthataredestroyedonlyinstratosphere(NO2andCFCs),tropospheric
lifetime≈stratosphericlifetime(althoughforremoval,gasesmustfirstbe
transferredtostratosphere,intimescale3years).
*Wholeoverturningofthermohalineoceancirculationis1000-2000years.
**Ozoneisproducedanddestroyedinsituintheatmosphere(notemitteddirectlyas
O3).Instratosphereozonelayerismaintainedbyconstantproductionand
destructionofozone(byUV-radiation)inphoto-chemicalreactioncycles.Lifetimeis
variable(butgenerallyozonelifetimeisshort,<1year)anddependsonlocal
conditionsintheatmosphere.
***adjustedlifetimethattakesintoaccountthefeedbackthatmethanehasonits
ownremovalrate(methanereactswithOH;reactionOH+CH4presentsabout30%
ofOHremovalrate=>methanedecreasesOH=>lossrateofmethanedecreasesalso;
withoutthisadjustmentmethanelifetimewouldbeabout8years)
****Source:http://www.atmos-chem-phys.net/13/6921/2013/acp-13-69212013.pdf
*****Source:Table7.1(Harvey)
5.Explainthefollowingterms/answershortly:
a)biologicalpumpintheocean
ThebiologicalpumpistheprocessinwhichCO2fromthesurfacewateris
transferredbybiologicalorganismstothedeepocean.Thishappensasdead
organismsinoceansurfacelayers(phyto-andzooplankton,marineanimaldebris
andskeletons,whichhavestoredcarbonintheirstructures*)sinktodeepwaters,(>
1km)resultinginstorageofcarbonforperiodsofdecadestocenturiesoreven
permanentlyinthesediments.
Photosynthesisintheoceanstakesupabout50Gtofcarbon/year.Totalcarbonflux
thatbiologicalpumptransfersisabout10GtC/year.About60-80%ofthisfluxisdue
tofallingsofttissue,andtherestisfallingCaCO3particles.Thebiologicalpumpalso
transfersnutrients(mainlyphosphorousandnitrogen)intodeepwaters.
Duetobiologicalpump,theoceancantakealotmorecarbonthanwithoutit!
*Themarineorganismsstorecarboneitherby
1)photosynthesis(reactionCO2+H2O->CH2O+O2,inphytoplanktonandother
plantorganisms),or
2)constructionofcalcareousskeletonsandshells(inreactionCa2++2HCO3-->
CaCO3+H2O+CO2,inshell/skeleton-buildingmarineanimals).Calciumcarbonate
CaCO3istheshell-buildingmaterialinmarineanimalssuchascoralsandoysters.
Note:BiologicalpumpmaybeaffectedwhenoceanpHdecreases(ocean
acidification)!
b)INDCs=IntendedNationallyDeterminedContributions
INDCsarevoluntarycommitmentsofgreenhousegasemissionreductionsthat
countriesintheworldhavesubmittedbeforetheParisclimateconference(COP21
30.11.-11.12.2015).InINDCeachcountrytellshowmuchitiswillingtoreduce
emissionsinfuture.Howemissionreductionsareexpressedvariesbetweenthe
countries,someexpressthetargetrelativetoemissionsin1990(traditional
referenceyearinKiotoprotocol),somerelativesomeotheryear,e.g.2005(USA),
somerelativetoGDP(China).Beforetheconference,INDCswerereceivedfrom
about180countries,coveringmorethan90%ofglobalemissions.
YoucanchecktheactualsituationofsubmittedINDCshere:
http://climateactiontracker.org/indcs.html