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  • ClimateChangeScience:whatdoweknow?

    GeraldLehmacherDepartmentofPhysicsandAstronomy

    15March2018

  • Quote

    UrsulaLeGuin (19292018), in:TheDispossessed,1974

  • ClimatePoll 1of3

    Doyouthinkglobalwarmingishappening? A.Yes B.No C.Dontknow

    http://climatecommunication.yale.edu

  • ClimatePoll 2of3

    Assumingglobalwarmingishappening,doyouthinkitis A.Causedmostlybyhumanactivities B.Causedmostlybynaturalchangesintheenvironment C.Other D.Noneoftheabovebecauseglobalwarmingisnthappening

  • ClimatePoll 3of3

    Tothebestofyourknowledge,whatpercentageofclimatescientists thinkthathuman-causedglobalwarmingishappening? A.90-100% B.70-90% C.50-70% D.Lessthan50% E.Dontknow

  • Isitjusttheweather,isittheclimate,

    orisitclimatechange?

  • Isitweather,climate,orclimatechange?

    Flashfloodsandtornadoes inSouthandMidwest,Feb24,2018

  • Isitweather,climate,orclimatechange?

    10cmsnowinRomeonFebruary26,2018.Photo:AP

  • Isitweather,climate,orclimatechange?

    Multi-yeardrought inSouthAfricadeclaredNationalDisaster,13March2018

  • Isitweather,climate,orclimatechange?

    Seventeennamedstorms,sixmajorhurricanesinAtlanticseason2017

    Inonephoto:Irma,Jose,Katia

  • Isitweather,climate,orclimatechange?

    12

    Thermokarst,thawponds inN.Quebec,http://www.bethanydeshpande.com/wp/

  • FrequentlyAskedQuestion:Areorwilltherebemorehurricanes?

    Years 1851-2016(2017:17)http://www.aoml.noaa.gov/hrd/tcfaq/E11.html

    ACE=AccumulatedCyclonicEnergy(2017:highestonrecord)

  • RulesofThumbforawarmerworld(confirmedbyobservationsandpredictedbymodelswithhighcertainty)

    - moreheatrecords- lesscoldrecords

    - moreheatwaves- largerdownpours, flashfloods

    - wetplacesgetwetter- dryplacesgetdrier

    - lesssnowpack- earliersnowmelt

    - prolonged droughts- strongertropicalstorms(notcertain)

  • 2017

    https://science2017.globalchange.gov/chapter/executive-summary/

  • 2015

  • https://www.nasa.gov/press-release/long-term-warming-trend-continued-in-2017-nasa-noaa

    2018

  • Abriefhistoryofmodernclimatechange

    Jean-BaptisteJosephFourier (1768-1830)

    developsatheoryofheatanddiscoversEarthsgreenhouseeffect.

    EarthssurfaceiswarmerthanheatingfromSunalonewouldimply.

  • Abriefhistoryofmodernclimatechange

    JohnTyndall(1820-1893)

    discoverstheabsorption ofinfraredradiationbymoleculeslikeCO2,H2O,N2O,CH4,O3

    Thesearetheatmosphericgreenhousegases

  • 22

    TheSun,ourcentralstar,radiatesenergyat3.8x1026 W,mostlyatvisiblewavelengths400-800nm

    someasXrays,UV,andnearIR

  • 23

    Thispowerisdilutedwiththedistancesquared(1/r2).AttheEarth,thesolarconstantisstillS=1370W/m2

  • 24

    TheEarthcollectssolarpoweracrossitsshadowareaofS(R2)allthetimeatthetopoftheatmosphere(likeinlow-earthorbit)

  • s

    CloudsandiceonEarthreflectabout30%backtospace(albedo)

  • 26

    Ifwebalance

    Energy(in)=Energy(out)

    S(1-)/4 =T4,with

    =5.67x10-8 Wm-2K-4

    wefind thesurfacetemperatureas

    T=[S(1-)/(4)]1/4

    T=255K(18C)

    whichismuchcolderthattheobservedaveragetemperature!

    Thesunlight reachesandwarms theEarthssurface,sincetheatmosphere ismostlytransparent forvisible light.

    TheentireEarthssurface(4R2)mustlose theenergybythermalradiationtospace.

  • 27

    Thesurfacesreceivessolarradiationandbackradiationfromtheatmosphere.Theresultingsurfacetemperatureis303K(abittoowarm,realvalue289K=16C)

    Weneedtoconsideranatmospherethatisopaquefortheoutgoinginfraredradiation

    238Wm2 =S(1-)/4 255Kcold

    303Kwarm

  • wikipedia

  • InfraredactivemoleculesItsquantumphysics!

    SymmetricbendofCO2 near667cm-1(15m)ismostimportantforgreenhouse effectonEarth(despiteitsmallmixing ratiosof400ppm).AlsoonVenusandMars.

    Watervapor(H2O,10000ppmbutvariable)absorbsatmanywavelengthsinnearandmiddle infrared.

    Themorebonds, themoreabsorptionlines.Therefore,CH4 (1.86ppm)andCFCs andHFCs arealsoimportantgreenhouse gasesthatcount.

    N N O O areIRinactive

  • Thisisanexplanationofthenaturalgreenhouseeffectinitssimplestform

    Itkeepsoceansliquid forprobablyall1 ofEarthshistoryof4.6Gy

    Refinements:Heatisalsotransportedawayfromthesurfacebyconvectionandlatentheat.Thetemperaturestructureisthereforebetterdescribedasradiative-convectiveequilibrium (Manabe andWeatherald,1967).

    Mostimportantgreenhouse gasesarewatervapor,whichisrecycledinafewdays,andcarbondioxide,whichislong-livedwithtimescalesof100sto10,000sofyears.

    Watervaporcontentincreaseswithincreasingtemperature,whichisthemostimportantpositiveclimatefeedback.

    1 SnowBallEarth,FaintSunParadox,veryhighCO2 content inCarboniferous

  • Trenberth,2009

  • Abriefhistoryofmodernclimatechange

    SvanteArrhenius (1859-1927)

    firstspeculatedthathumans fossilfuelburningandaddingcarbondioxidemayraisethetemperatureoftheEarth

    moregreenhousegasesenhancethenaturalgreenhouseeffectandcauseglobalwarming

  • Abriefhistoryofmodernclimatechange

    CharlesDavidKeeling(1928-2005)

    startssystematicmeasurementsofcarbondioxideandshowsthattheyareeverincreasing

    Globalcarbondioxide levelsarenowhigherthantheywereinthepastmillionyearsandhaveincreasedfrompreindustrial levelsof280ppmtoover406ppmduetohumanfossil-fuelburning,deforestationandchangesinlanduse

    AbouthalfoftheemittedCO2isbeingdissolved intheoceans(acidification), theotherhalfremainsintheatmospherefor100yearsandevenmuchlonger

  • Keelingcurve

  • Abriefhistoryofmodernclimatechange

    JamesEdwardJimHansen(b.1941)

    developsglobaltemperaturesetsandglobalclimatemodelsatNASAsincetheearly1980s,

    whichshowthattheobservedwarmingcanonlybemodeledandexplainedbyincluding theradiativeforcing thehumancausedgreenhouse emissionsandassociatedfeedbacks,suchasice-albedodecreasesandwatervaporincreases

    HetestifiesabouthisresultsbeforeCongressfirstin1988.

    Averageglobal temperaturesarenowwarmerthaneverinthepast400,000years(during previous interglacials,warmperiodsbetweeniceages)

  • Thelandwarmsfasterthantheocean;theoceanabsorbs98%oftheextrawarming,expandsandcausessealevelrise.

    morethan1C(1.8F)increase!

  • Surprisingly well(paperbyGavinSchmidt,2009).A,B,Caredifferentemissionscenarios

  • IPCC

  • OtherevidenceforclimatechangeFromthe2017U.S.ClimateChangeSpecialReport

    Inadditiontowarming,manyotheraspectsofglobalclimatearechanging,primarilyinresponsetohumanactivities.Thousandsofstudiesconductedbyresearchersaroundtheworldhavedocumentedchangesinsurface,atmospheric,andoceanictemperatures;meltingglaciers;diminishingsnowcover;shrinkingseaice;risingsealevels;oceanacidification;andincreasingatmosphericwatervapor.

  • Debunkingclimatemyths

    https://skepticalscience.com

    https://insideclimatenews.org/news/22112017/thanksgiving-family-climate-denial-global-warming-science-answers

  • Debunkingclimatemyths

    http://www.realclimate.org

  • MerchantsofDoubt

    42

    Book(2010)

    Movie(2014)

    https://www.youtube.com/watch?v=j8ii9zGFDtc

    repeatofthetobaccostrategyofthe1960s

  • Currentissuesinclimatescience

    43

    https://www.nature.com/nclimate/

  • Currentissuesinclimatescience

    44

  • Currentissuesinclimatescience

    45

  • Currentissuesinclimatescience

    46

    http://www.sciencemag.org

  • Solutions

    wemustreduceglobal fossilfuelemissionsasquicklyaspossible

    Ifwewanttolimittheeffectsofglobalwarming,

    (forexample,by+1.5Ctemperatureincreaseoverpre-industrialby2100)

  • CarbonCaptureandStorage(CCS)

    48

    possiblyaidedby

  • Geoengineering

    49

    asalastresort?

    inparticular,solarradiationmanagement,i.e.dimmingtheSunwithintroducingstratosphericaerosolsonaglobalscale,likemajorvolcaniceruptions do

    mustbecontinued indefinitely oruntilothersolutions arise

    https://www.theguardian.com/environment/blog/2012/feb/06/artificial-volcano-cool-planet-sun

  • Thankyouforyourattention

    51