DecadalPredic+ons:StateoftheScience

E.TowlerEaSMMee+ng,NCAR

Jan20,2015

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Whytheemphasisondecadalpredic+ons?

•  Societalneedfornearterm/decadalpredic+onsofclimatefordecisionsupport(Veraetal.2010)•  Actual+meevolvingpredic+onsratherthan

unini+alizedprojec+ons1.

•  Researchshowspoten-al(andsomeevidence)forpredic-onskillondecadal+mescales

•  Lesssensi-vetoemissionsscenario

Kirtmanetal.2013,IPCC

1IPCCdefini+onispredic+onsareini+alized,projec+onsareunini+alized

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Emissionsscenariolessimportantondecadal+mescales

HawkinsandSuWon2009

•  CMIP5decadalpredic+onsusedtheRCP4.5scenario.(Meehletal.2014)

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Figure2Meehletal.2009BAMS

BridgegapbetweenENSOforecas+ngandfutureclimatechangeprojec+ons

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Figure2Meehletal.2009BAMS

BridgegapbetweenENSOforecas+ngandfutureclimatechangeprojec+ons

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ENSOevolvesmoreslowly:6-12months

Synop+cweather:2weeks(Lorenz1963)

Long-termtrendsbasedonGHGforcing

What’sthe“sweetspot”?(out10-30yearsdefinedas“decadal”)

WhataretheCMIP5decadalpredic+ons?

Tayloretal.2012BAMS

•  Twocoresetsofnear-termexperiments•  10-year

hindcasts•  30-year

hindcasts(outto2035)

•  Specializedsimula+onop+ons

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Aimistounderstandpredic+bility,meritsofdataassimila+onapproaches,andlimita+onsofcurrentobserva+ons

Tayloretal.2012BAMS 7

Decadalpredic+onsandprojec+onshavebuilt-inskill1from:

1  Climatechangecommitment

2  Theforcingfromincreasinggreenhousegases

Meehletal.2009;Leeetal20061Barringvolcanicerup+on

CMIP3modelscanalreadysimulatethemagnitudeofobserveddecadalsurfacetemperaturevariabilityoverland(IPCC2007WGIFig9.8)

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}Radia+ve/externalforcing

•  Ini-aliza-oncontributesmostskillin•  firstfewyears:annualmeantemperature•  afewyearstoadecade:globalmeansurfacetemperatureandtemperatureovertheNorthAtlan+c,regionsoftheSouthPacificandthetropicalIndianOcean

•  Radia-veforcingcontributesmostskill

•  Beyondfirstfewyears:forannualandmul+-annualaveragesoftemperatureandprecipita+on

Skillfromini-aliza-onversusradia+veforcingdependson+mehorizon,variable,&

region

Kirtmanetal.2013,IPCC9

•  Forini+alizeddecadalhindcasts,mul-modelensembleoutperformsmostsinglemodelresults(Chikamotoetal.2012a,Kimetal.2012,andSmithetal.2012b.)(FromMeehletal.2014BAMS)

•  Poten+alpredic+bility:•  Greaterforoceanheatcontentthanatmosphericorland

variables(HermansonandSuWon2010)(FromKirtmanetal.2013IPCC)

•  Oceanskillincreaseswithla+tudeanddepth(PowerandColman2006)(FromKirtmanetal.2013IPCC)

•  Greaterathigherla+tudes(extratropicaloceans)thanoverland(Figure11.1,Kirtmanetal2013,IPCC)

•  Lowerfortropicsandoverland,whereskillmostlyfromexternalforcing(Figure11.1,Kirtmanetal.2013,IPCC)

Somegeneralfindings

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Decadalphenomenathatcouldcontributetoskill

•  Pacific•  11-yearsolarcyclewithtropicalPacificSSTs•  PacificDecadalOscilla+on(PDO),NorthPacific

Index(NPI),InterdecadalPacificOscilla+on(IPO)

•  Atlan-c•  Atlan+cmeridionaloverturningcircula+ons

(AMOCs)•  Strong+eswithNorthAtlan+cOscilla+on

•  Atlan+cMul+decadalOscilla+on(AMO),Atlan+cmul+decadalvariability(AMV)

Meehletal.2009 11

Technicalchallengesremain•  Modelini-aliza-on/dataassimila-on•  Manydifferentmethodsbydifferentmodeling

groups(Table1,Meehletal.20014BAMS)

•  Fordril:Full-fieldini+aliza+onvsanomalyini+aliza+on(Meehletal.2014BAMS)

•  Limitedavailabilityofobserva-ons(Goddardetal.2012BAMS)

•  Dynamicalmodellimita-ons(Goddardetal.2012BAMS)

Kirtmanetal.2013,IPCC12

Technicalchallengesremain•  Predic-onsrequirebiasadjustment1•  Modelsdrilfromtheobservedini+alstatetoits

ownpreferredstate,some+mesrapidly.•  Meanbiasadjustmentdoesnotaddressissuessuch

aspoten+altrends(+medependence)inthedril/bias.•  i.e.,correc+onismorecomplicatedthanfor

centennialruns.Fig.1.Meehletal.2014BAMS

1CMIP–WGCM–WGSIPDecadalClimatePredic+onPanel,2011:Dataandbiascorrec+onfordecadalclimatepredic+ons.WCRPRep.,ICPOPubl.Series150,3pp.[Availableonlineatwww.wcrp-climate.org/decadal/references/DCPP_Bias_Correc+on.pdf.]

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•  “Mostuserswillfinditdifficulttobiascorrectthedecadalpredic+onruns;itisthereforerecommendedthatanalysisofthenear-termsimula+onsbelimitedtothefourvariablesthatthemodelinggroupsthemselvesplantobiascorrect:near-surfaceairtemperature,surfacetemperature,precipita-onrate,andsealevelpressure.”*

Tayloretal.2012BAMS

Recommenda+onforbiascorrec+on:

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*I’mnotsureifCMIP5archiveincludesbias-correctedfields–needtocheck.

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Biascorrec+onop+onfor30-yearhindcast:

•  Onemethodistousetheyear10biasadjustmentforyears11–30,assumingmostofthedriloccursbyyear10(MeehlandTeng2012,2014).

(Towleretal.,2012AGUposter)

Goddardetal.2012ClimDyn

Predic+onqualityneedstobeassessedusingacommonverifica+onframework

Needtousecommonobs

hWp://clivar-dpwg.iri.columbia.edu/

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Meehletal.2014BAMS

Temp:Widespreadpredic+veskillofpredic+onsvs.observa+ons.

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Temp:Lessskilladdedfromini+aliza+on,variesspa+ally

Meehletal.2014BAMS 18

Oceansshowhighestskill,butskillsourceandregionsvary

•  IndianOcean•  Showshighestsurfacetempskill–duetoexternalforcing

fromGHGs(soprojec+onsarealsoskillful)

•  Atlan-cOcean•  Manystudiesfindthatini+aliza+onimprovesthepredic+ve

skilloftemperatureintheNorthAtlan+c–par+allyduetoskillfulAMOCpredic+on.

•  SomeencouragingresultsfortropicalAtlan+c

•  PacificOcean•  LessskillthanIndianandAtlan+cOcean

•  InterannualvariabilityfromENSO,butdebateonrela+onshipbetweenENSOanddecadaloscilla+onslikePDO.

•  Somestudiesdoshowsomeimprovedskillfromini+aliza+on,esp.inWestern&SouthPacific

Meehletal.2014BAMS19

Precipita+onislessskillfulthantemp

Meehletal.2014BAMS

20Precipita+onskillcanbeaWributedmostlytoradia+veforcing(highconfidence),ini+aliza+onimprovestheskillveryliWle(Goddardetal.,2013).“

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Someskillinpredic+ngextremetemperaturesandprecipita+on•  10%likelihoodofoccurrence(moderateextremes)

•  MetOfficeDecadalPredic+onSystem(DePreSys)

•  Skillinextremesissimilarbutslightlylowerthanformean•  Someexcep+onswheretherearetrendsinextremes(e.g.,USAcoldnights).

•  Overmul+years,skillisfromexternalforcing•  Skillinsummerextremeindices,mostlyfromexternalforcing;DePreSys(Hanlonetal.2013)

Eadeetal.2012

•  SkillfulNorthAtlan+cOceanSSTscouldimprove(i)rainfalloverAfricanSahel,India,andBrazil,(ii)Atlan+churricanes,and(iii)summerclimateoverEuropeandAmerica.

•  SkillfulPacificSSTscouldimproverainfalloverNorthandSouthAmerica,Asia,Africa,andAustralia.

•  SkillfulPacificandAtlan+cSSTscouldimprovedroughtpredic+onoverUS.

Decadaloceanskillcouldleadtoskillfulpredic+onsoverland

Meehletal.2014BAMS 22

Ini+alizedpredic+onsshowlesswarmingthanprojec+ons.

23Kirtmanetal.2013,IPCC

Figure11.9b

Decadalpredic+onsarenotconsidered“opera+onal”

•  “decadalpredic+ons…areinanexploratorystage”(Tayloretal.2012BAMS)

•  “…verymuchanexperimentalandnascentac+vity.”(Goddardetal.2010ClimDyn)

•  “Duetothelimita+ons,thees+matesobtainedfromthehindcastsmayprovideapoor,andevenmisleading,guidetothefutureperformanceofthedecadalpredic+onsystems.”(Goddardetal.2010ClimDyn)

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Decadalpredic+onshavemanyfeaturesincommonwithseasonalforecasts

Goddardetal.2012BAMS;Goddardetal.2012ClimDyn.

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Goddardetal.2012BAMS

Seasonalforecastscanprovideatestbedfordecadalpredic+ons.

•  Buildtrust:Seasonalforecastsofferopportunitytodemonstrateperformanceovertherecentpastandoverthenextfewseasons/years.

•  Increaseuptake:Usingseasonalclimateinforma+onwillindirectlystrengthencapacityforusingclimateinfoonlonger+mescales.

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•  Seasonal-to-DecadalClimatePredic+onfortheImprovementofEuropeanClimateServices(SPECS)

•  “MiWelfris+geKlimaprognose”Germany(meaningdecadalclimatepredic+on)(MiKlip)

•  Newsetofdecadalclimatepredic+onsexperimentsintoCMIP6.

Addi+onal/Upcomingdecadalpredic+onexperiments

Meehletal.2014BAMS 27

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Thewayforward•  Increaseunderstandingofclimateandsocialinfluenceson

impacts•  Leveragepredic+onsinplaceswhereini+aliza+onimproves

skill(e.g.,NorthAtlan+c)•  Leverageprojec+onsinplaceswhereskillisduetoexternal

forcing(e.g.,IndianOcean)(*ThisismostlywhatIPCC2013does;alsocancomparepredic<onsandprojec<ons-extremes?).

•  LeverageNCARmedium/largeensemblewhereinternalvariabilityisimportant(e.g.,localimpacts)

•  Developgeneralizedframeworkthatwillbereadywhendecadalpredic+onsimprove–  Useseasonalforecas+ngasa“testbed”–  Inves+gatehowto“best”incorporatedecadalpredic+onsindecisions

–  Inves+gate“best”communica+onofdecadalpredic+ons

ReferencesEade,R.,Hamilton,E.,Smith,D.M.,Graham,R.J.,&Scaife,A.a.(2012).Forecas+ngthenumberofextremedailyeventsouttoadecadeahead.JournalofGeophysicalResearch:Atmospheres,117(D21),doi:10.1029/2012JD018015Goddard,L.,Hurrell,J.W.,Kirtman,B.P.,Murphy,J.,Stockdale,T.,&Vera,C.(2012).TwoTimeScalesforThePriceOfOne(Almost).Bulle+noftheAmericanMeteorologicalSociety,93(5),621–629.doi:10.1175/BAMS-D-11-00220.1Goddard,L.,Kumar,A.,Solomon,a.,Smith,D.,Boer,G.,Gonzalez,P.,…Delworth,T.(2012).Averifica+onframeworkforinterannual-to-decadalpredic+onsexperiments.ClimateDynamics.doi:10.1007/s00382-012-1481-2Hanlon,H.M.,G.C.Hegerl,S.F.B.TeWandD.M.Smith,2013:Canadecadalforecas+ngsystempre-dicttemperatureextremeindices?J.Climate,26,3728–3744.Hawkins,E.,&SuWon,R.(2009).ThePoten+altoNarrowUncertaintyinRegionalClimatePredic+ons.Bulle+noftheAmericanMeteorologicalSociety,90(8),1095–1107.doi:10.1175/2009BAMS2607.1Meehl,G.A.,Goddard,L.,Boer,G.,etal.(2014).DecadalClimatePredic+on:AnUpdatefromtheTrenches.Bulle+noftheAmericanMeteorologicalSociety,95(2),243–267.doi:10.1175/BAMS-D-12-00241.1Meehl,G.A.,Goddard,L.,Murphy,etal.(2009).DecadalPredic+on.Bulle+noftheAmericanMeteorologicalSociety,90(10),1467–1485.doi:10.1175/2009BAMS2778.1Meehl,G.A.,&Teng,H.(2012).Casestudiesforini+alizeddecadalhindcastsandpredic+onsforthePacificregion.GeophysicalResearchLeWers,39(22),doi:10.1029/2012GL053423Taylor,K.E.,Stouffer,R.J.,&Meehl,G.A.(2012).AnOverviewofCMIP5andtheExperimentDesign.Bulle+noftheAmericanMeteorologicalSociety,93(4),485–498.doi:10.1175/BAMS-D-11-00094.1Vera,C.,Barange,M.,Dube,O.P.,Goddard,L.,Griggs,D.,Kobysheva,N.,…Trenberth,K.(2010).NeedsAssessmentforClimateInforma+ononDecadalTimescalesandLonger.ProcediaEnvironmentalSciences,1(5),275–286.doi:10.1016/j.proenv.2010.09.017 29