geog 401 climate perturbations - university of...
TRANSCRIPT
GEOG401ClimateChange
ClimatePerturba6ons:ForcingsandFeedbacks
ConceptualizingtheClimateSystem
“Earth’sclimateistheresultofthephysicalrequirementtomaintainabalancebetweenenergyreachingandleavingtheatmosphere.”(Cornelletal.,eds.,2012,p.72)“HeatistransportedaroundtheEarthinboththeatmosphereandtheocean,andthepaPernsofthistransportmodulateclimateatanygivenloca6on.”(Cornelletal.,eds.,2012,p.72)
ClimatePerturba6ons
Defini6on:perturba6on–adevia6onofasystemcausedbyanoutsideinfluence(hPp://oxforddic6onaries.com/defini6on/english/perturba6on)
ClimateForcings“Inclimatescience,radia6veforcingisdefinedasthedifferencebetweenradiantenergyreceivedbytheearthandenergyradiatedbacktospace.”(hPp://en.wikipedia.org/wiki/Climate_forcing)“Arangeof‘primary’forcingscanbeconsideredexternaltotheclimatesystem:theseinclude“changesintheamountofincomingsolarradia6on(insola6on)causedbychangesintheEarth’sorbit,orchangesinsolarac6vity.“Volcanicac6vity,whichreleasestracegasesandpar6culatesintheatmosphere,isalsogenerallythoughtofasanexternalforcingontheclimatesystem.“Anthropogenicandgeologicemissionsofgreenhousegasesarealsogenerallyconsideredasprimaryforcings.”(Cornelletal.,eds.,2012,p.73)
Feedbacks“Feedbackingeneralistheprocessinwhichchangingonequan6tychangesasecondquan6ty,andthechangeinthesecondquan6tyinturnchangesthefirst.Posi6vefeedbackamplifiesthechangeinthefirstquan6tywhilenega6vefeedbackreducesit.”(hPp://en.wikipedia.org/wiki/Climate_change_feedback)“Climatechangefeedbackisimportantintheunderstandingofglobalwarmingbecausefeedbackprocessesmayamplifyordiminishtheeffectofeachclimateforcing,andsoplayanimportantpartindeterminingtheoverallclimatesensi6vity.”(hPp://en.wikipedia.org/wiki/Climate_change_feedback)
ClimateForcingsand/orFeedbacks
• Solaroutput(Forcing)– Long-termincrease– Sunspotcycle– Anomaliesinsunspotcycle(e.g.,MaunderMinimum)
• Orbitalcharacteris;cs(Forcing)– MilankovitchCycles
• Atmospherictransmission(ForcingorFeedback)– Volcanicerup6ons– Dust,smoke,etc.
• Earthalbedo(ForcingorFeedback)– Ice/snowcoverchanges– Changesincloudcover/characteris6cs
• Atmosphericlongwaveradia;onabsorp;on(ForcingorFeedback)– Varia6onsingreenhousegasconcentra6ons
GreenhouseGasForcing
hPp://www.giss.nasa.gov/research/news/20020114/
GreenhouseGasForcing
hPps://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing
SolarOutputSolarEvolu;onFaintEarlySunParadox:“4.5billionyearsagosunwasca.8%smallerand3%lessluminoussosolarconstantwasca.25%less.”(WalterandBarry,1991)(hPp://www.geo.arizona.edu/palynology/geos462/20climsolar.html)
SolarOutputSunspotCycle
SolarOutputSunspotCycle
SolarOutputSunspotCycle
SolarOutputSunspotCycle
SolarOutputSunspotCycle
MilankovitchCycles• Thecharacteris6csofEarth’sorbitandaxial6lt
changeinregularcycles.• ThishasliPleinfluenceonthetotalannual
energyintercep6onofthewholeEarth• Seasonalandla6tudinaldistribu6onofenergy
issignificantlyaffectedcausingchangesinpolaricecover
• IcecoverchangesaffectEarth’salbedo
Cycles• Obliquity(22.1–24.5degrees;41,000-yrcycle;
currently23.44degrees)• Eccentricity(0.005–0.058);100,000-yrcycle;
currently0.017)• Precession(21,000-yrcycle)
MilankovitchCycles
εisobliquity(axial6lt)
ϖislongitudeofperihelion
esin(ϖ)istheprecessionindex(eiseccentricity)
isthecalculateddaily-averagedinsola6onatthetopoftheatmosphere,onthedayofthesummersols6ceat65Nla6tude
ConsequencesofOrbitalVaria6ons
DatafromVostokicecores:hPp://www.usgcrp.gov/usgcrp/images/Vostok.jpg
VolcanicErup6ons
hPp://www.climate4you.com/ClimateAndVolcanoes.htm
VolcanicErup6ons
hPp://www.geog.cam.ac.uk/research/projects/volcanoeffects/
VolcanicErup6onsVolcanicEmissions• Dustpar6cles• Sulfurcompounds• Watervapor• Carbondioxide
Tambora(1815)• 150km3ofash• 900kmfromtheerup6on,1cmofashfell• Erup6oncolumnes6matedtohavebeen45kmhigh• Est.92,000peoplekilledbyerup6on• Loweredglobalaveragetemperatureby0.5-0.7degC
over2-3years• Yearwithoutasummer(1816)• LondonhadsnowinAugust
VolcanicErup6onsKrakatau(Krakatoa)(1883)
• Loudestsoundinmodernhistory(heardupto4,800milesaway)
• Op6caleffectsforseveralyears
VolcanicErup6onsPinatubo(1991)
VolcanicErup6onsPinatubo(1991)
Longman(2012)
Ice-AlbedoForcing/Feedback
Ice-AlbedoForcing/FeedbackFortheArc;cOcean,forexample:• Snow-coveredicealbedo:80-90%• Openoceanalbedo<10%• Changesinseaiceextenthavelargeimpactsonalbedoofthepolarregion• Ice-albedoeffectonshortwaveradia6onabsorp6onissomewhatless
becauseofatmosphericreflec6on,especiallybyclouds• Temperaturevaria6onaffectsseaiceextentonlywithinacertainrange;
whentemperaturesareverylow,temperaturevaria6onsdonotresultinmel6ng;whentemperaturesarehigh,temperaturevaria6onsdonotresultinfreezing
• Effectsonenergybalancedependontherela6veeffectsoftemperaturechangeonalbedo(affec6ngshortwaveabsorp6on)andemission(longwave)
Ice-AlbedoForcing/Feedback
hPp://www.gfdl.noaa.gov/bibliography/related_files/mw0901.pdf
Ice-AlbedoForcing/Feedback
hPp://www.gfdl.noaa.gov/bibliography/related_files/mw0901.pdf
Ice-AlbedoForcing/Feedback
hPp://www.gfdl.noaa.gov/bibliography/related_files/mw0901.pdf
Ice-AlbedoForcing/FeedbackForlandareas,suchasGreenlandandAntarc6ca:• Theicevs.ice-freealbedocontrastis
somewhatlessthanfortheocean
Snow-AlbedoForcing/FeedbackVegetatedlandareassuchasborealforests:• Evergreentreecoverreducesthealbedoeffectofsnow
hPp://www-modis.bu.edu/brdf/userguide/publica6ons/2002_jin_2_etal.pdf
CloudForcings/Feedbacks
Albedofeedback
Longwaveabsorp6onfeedback
hPp://earthobservatory.nasa.gov/Features/Clouds/
CloudForcings/Feedbacks
NetRadia6on
NetCloudRadia6veForcing
hPp://earthobservatory.nasa.gov/Features/Clouds/
GreenhouseForcing/Feedback
AR5WG1Draqreport(2013,Chapter2)
hPps://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing
GreenhouseForcing/Feedback
hPp://www.giss.nasa.gov/research/briefs/schmidt_05/
ClimateSensi6vityClimateSensi;vity=changeinmeansurfaceairtemperatureinresponsetoagivenradia6veforcingTwotypesofclimatesensi;vity:ECS:EquilibriumClimateSensi6vityTCR:TransientClimateResponse
ClimateSensi6vityClimateSensi6vityisafundamentalcharacteris6coftheclimatesystem.Ifitwereknownwithcertainty,asimpleenergybalancemodelcouldbeusedtopredictthetemperaturechange.
ΔTs / RF = λwhere :Ts = Earth's mean surface air temperature ( C)RF = radiative forcing (W m−2 )λ = climate sensitivity ( C per W m−2 )
ClimateSensi6vity
ClimateSensi6vitytoincreasesinatmosphericgreenhousegasesisusuallygivenasthetemperaturechangethatwilloccurwithadoublingofCO2concentra6onrela6vetothepre-industriallevel.
ClimateSensi6vityClimateSensi6vityises6matedfromglobalclimatemodelsandusingpaleo-analogues.
Model-basedes6matesofclimatesensi6vity:Differencesamongclimatemodelsintheirclimatesensi6vityisameasureoftheuncertaintyinclimateprojec6ons.
hPp://earthobservatory.nasa.gov/blogs/climateqa/what-if-global-warming-isnt-as-severe-as-predicted/
Thisimageshowsfrequencydistribu6onofclimatesensi6vity,basedonmodelsimula6ons.BasedonthecitedLindsey(2010)public-domainsource:Tounderstandhowuncertaintyabouttheunderlyingphysicsoftheclimatesystemaffectsclimatepredic6ons,scien6stshaveacommontest:theyhaveamodelpredictwhattheaveragesurfacetemperaturewouldbeifatmosphericcarbondioxideconcentra6onsweretodoublepre-industriallevels(theclimatesensi6vity)
ClimateSensi6vityPaleo-analoguees6matesofclimatesensi6vity:
ClimateSensi6vityPaleo-analoguees6matesofclimatesensi6vity:1. Howaccuratelyknownarethecharacteris6csof
thepastclimatesandforcings?2. Isthecontemporaryclimatesystemresponse
unchangedfromthe6meofthepaleo-analogues?
ClimateSensi6vity
hPp://www.iac.ethz.ch/people/knutr/papers/knut08natgeo.pdf
ClimateSensi6vity
hPp://www.iac.ethz.ch/people/knutr/papers/knut08natgeo.pdf
ClimateSensi6vity
hPp://www.iac.ethz.ch/pe
ople/knu
tr/pape
rs/knu
t08natgeo
ClimateSensi6vityWhenwillwegettodoubledCO2?
RCP:Representa;veConcentra;onPathwaysScenarioshPp://www.skep6calscience.com/print.php?n=1866
JamesHansenBjerknesLecture2008AGUFallMee6ng
hPps://www.youtube.com/watch?v=9I_KkBtwI-o
Seeclimatesensi6vitydiscussionstar6ngaround9minutesintothevideo
AR5ClimateSensi6vityEs6mates
• EquilibriumClimateSensi6vity(ECS):likelytobebetween1.5°Cand4.5°C
• ECSextremelyunlikelytobelessthan1°C• ECSveryunlikelytobegreaterthan6°C• TransientClimateResponse(TCR):likelytobebetween1.0°Cand2.5°C
• TCRextremelyunlikelytobegreaterthan3°C
AR5EndofCenturyWarming
3.2°Cto5.4°Crela6vetothe1850-1900baselineforthehighemissionsscenario(RCP8.5)