Download pdf - Climate Change Science: what do we know? - …blogs.clemson.edu/emerituscollege/files/2018/03/C2018-Climate... · . html ACE = Accumulated Cyclonic Energy (2017: highest on record)

ClimateChangeScience:whatdoweknow?

GeraldLehmacherDepartmentofPhysicsandAstronomy

15March2018

Quote

UrsulaLeGuin (1929–2018), in:TheDispossessed,1974

ClimatePoll– 1of3

Doyouthinkglobalwarmingishappening?• A.Yes• B.No• C.Don’tknow

http://climatecommunication.yale.edu

ClimatePoll– 2of3

Assumingglobalwarmingishappening,doyouthinkitis…• A.Causedmostlybyhumanactivities• B.Causedmostlybynaturalchangesintheenvironment• C.Other• D.Noneoftheabovebecauseglobalwarmingisn’thappening

ClimatePoll– 3of3

Tothebestofyourknowledge,whatpercentageofclimatescientists thinkthathuman-causedglobalwarmingishappening?• A.90-100%• B.70-90%• C.50-70%• D.Lessthan50%• E.Don’tknow

Isitjusttheweather,isittheclimate,

orisitclimatechange?

Isitweather,climate,orclimatechange?

Flashfloodsandtornadoes inSouthandMidwest,Feb24,2018


10cmsnowinRomeonFebruary26,2018.Photo:AP


Multi-yeardrought inSouthAfricadeclaredNationalDisaster,13March2018


Seventeennamedstorms,sixmajorhurricanesinAtlanticseason2017

Inonephoto:Irma,Jose,Katia


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)

developsatheoryof“heat”anddiscoversEarth’s“greenhouseeffect”.

Earth’ssurfaceiswarmerthanheatingfromSunalonewouldimply.


JohnTyndall(1820-1893)

discoverstheabsorption ofinfraredradiationbymoleculeslikeCO2,H2O,N2O,CH4,O3

Thesearetheatmospheric“greenhousegases”

22

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

someasXrays,UV,andnearIR

23

Thispowerisdilutedwiththedistancesquared(1/r2).AttheEarth,the“solarconstant”isstillS=1370W/m2

24

TheEarthcollectssolarpoweracrossits“shadowarea”ofS(πR2)allthetimeatthe“topoftheatmosphere”(likeinlow-earthorbit)

s

CloudsandiceonEarthreflectabout30%backtospace(“albedo”)

26

Ifwebalance

Energy(in)=Energy(out)

S(1-α)/4 =σT4,with

σ=5.67x10-8 Wm-2K-4

wefind thesurfacetemperatureas

T=[S(1-α)/(4σ)]1/4

T=255K(–18°C)

whichismuchcolderthattheobservedaveragetemperature!

Thesunlight reachesandwarms theEarth’ssurface,sincetheatmosphere ismostlytransparent forvisible light.

TheentireEarth’ssurface(4πR2)mustlose theenergybythermalradiationtospace.

27

Thesurfacesreceivessolarradiationand“backradiation”fromtheatmosphere.Theresultingsurfacetemperatureis303K(abittoowarm,realvalue289K=16°C)

Weneedtoconsideranatmospherethatisopaquefortheoutgoinginfraredradiation

238Wm–2 =S(1-α)/4 255Kcold

303Kwarm

wikipedia

InfraredactivemoleculesItsquantumphysics!

SymmetricbendofCO2 near667cm-1

(15µm)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

Thisisanexplanationofthe”natural”greenhouseeffectinitssimplestform

Itkeepsoceansliquid forprobablyall1 ofEarth’shistoryof4.6Gy

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

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

Watervaporcontentincreaseswithincreasingtemperature,whichisthemostimportantpositiveclimatefeedback.

1 SnowBallEarth,FaintSunParadox,veryhighCO2 content inCarboniferous

Trenberth,2009


SvanteArrhenius (1859-1927)

firstspeculatedthathumans fossilfuelburningandaddingcarbondioxidemayraisethetemperatureoftheEarth

moregreenhousegasesenhancethenaturalgreenhouseeffectandcauseglobalwarming


CharlesDavidKeeling(1928-2005)

startssystematicmeasurementsofcarbondioxideandshowsthattheyareeverincreasing

Globalcarbondioxide levelsarenowhigherthantheywereinthepastmillionyearsandhaveincreasedfrompreindustrial levelsof280ppmtoover406ppmduetohumanfossil-fuelburning,deforestationandchangesinlanduse

AbouthalfoftheemittedCO2isbeingdissolved intheoceans(acidification), theotherhalfremainsintheatmospherefor100yearsandevenmuchlonger

“Keelingcurve”


JamesEdward”Jim”Hansen(b.1941)

developsglobaltemperaturesetsandglobalclimatemodelsatNASAsincetheearly1980s,

whichshowthattheobservedwarmingcanonlybemodeledandexplainedbyincluding theradiativeforcing thehumancausedgreenhouse emissionsandassociatedfeedbacks,suchasice-albedodecreasesandwatervaporincreases

HetestifiesabouthisresultsbeforeCongressfirstin1988.

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

Thelandwarmsfasterthantheocean;theoceanabsorbs98%oftheextrawarming,expandsandcausessealevelrise.

morethan1°C(1.8°F)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

repeatofthe“tobaccostrategy”ofthe1960s

Currentissuesinclimatescience

43

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


44


45


46

http://www.sciencemag.org

Solutions

wemustreduceglobal fossilfuelemissionsasquicklyaspossible

Ifwewanttolimittheeffectsofglobalwarming,

(forexample,by+1.5°Ctemperatureincreaseoverpre-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