Consistency and robustness of selected emergent …3) Mixing–Lower tropospheric mixing index...
Transcript of Consistency and robustness of selected emergent …3) Mixing–Lower tropospheric mixing index...
Consistency and robustness of selected emergent constraints for equilibrium climate sensitivityAxel Lauer and Veronika Eyring
Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Oberpfaffenhofen, Germany
CFMIP Meeting on Cloud Processes, Circulation and Climate Sensitivity25-28 September 2017, Tokyo, Japan
Equilibrium climate sensitivity (ECS)
Charneyreport
IPCC FAR
IPCC SAR
IPCC TAR
IPCC AR4
IPCC AR5
DefinitionProjectedequilibriumchangeinglobalannualmeansurfacetemperaturefollowingadoublingoftheatmosphericCO2concentration.0.0
1.0
2.0
3.0
4.0
5.0
6.0
1979 1990 1996 2001 2007 2013
ECS(K)
Emergent constraints
Emergentconstraints arearelationshipacrossanensembleofmodels,betweensomeaspectofEarthsystemsensitivityand anobservabletrendorvariationinthecurrentclimate
• Anecessarypropertyofemergentconstraintsisaphysicalbasisfortherelation.
• Offerthepotentialtoreduceuncertaintyinclimatefeedbacksandprojections.
• Canhelpguidingmodeldevelopmentontoprocessescrucialtothemagnitudeandspreadoffutureclimatechange andtoguidefutureobservations.
Selected published emergent constraints for equilibrium climate sensitivity
SelectedpublishedemergentconstraintsforECS
1) Precipitation – SouthernITCZindex(Tian,2015)
2) Humidity – Tropicalmid-tropospherichumidityasymmetryindex(Tian,2015)
3) Mixing – Lowertroposphericmixingindex(LTMI)(Sherwoodetal.,2014)
4) Clouds – Covarianceofdeseasonalized tropicallowcloud(TLC)shortwavereflectionwithSST(Brient andSchneider,2016)
Testconsistencyamongdifferentproposedemergentconstraintsandtheirsensitivityto:
• Modelensemble(CMIP3,CMIP5)• Observationaldataset(s)
ESMValTool version 1.1.0
http://www.esmvaltool.org/Eyringetal.,Geosci.ModelDev.,2016
• Communitydiagnosticsandperformancemetricstool fortheevaluationofEarthSystemModels(ESMs)
• Standardizedmodelevaluation canbeperformedagainstobservations,againstothermodelsortocomparedifferentversionsofthesamemodel
• manydiagnosticsandperformancemetricscoveringdifferentaspectsoftheEarthSystem(dynamics,radiation,clouds,carboncycle,chemistry,aerosol,sea-ice,etc.)andtheirinteractions
• Well-establishedanalysisbasedonpeer-reviewedliterature
• Currently≈70developersfrom28institutionsand>100users
GitHub:https://github.com/ESMValGroup/ESMValTool
Southern ITCZ index (Tian, 2015)
SoutheasternPacific30°S-0°,150°W-100°W
• Climatologicalannualmeanprecipitationbias
• Model– observation(mmday-1)• AveragedoversoutheasternPacific
Observational data
1) GlobalPrecipitationClimatologyProject(GPCP,1980-2005)2) CPCMergedAnalysisofPrecipitation(CMAP,1980-2005)3) TropicalRainfallMeasuringMission(TRMM,1998-2013)
Southern ITCZ index (Tian, 2015)
4.0 K
TRMM, CMIP5
Southern ITCZ index (Tian, 2015)TRMM GPCP CMAP
CM
IP3
CM
IP5
4.0 K 3.8 K 3.7 K
4.1 K 3.8 K 3.7 K
Southern ITCZ index (Tian, 2015)
4.1 K
3.7 K
Tropical mid-tropospheric humidity asymmetry index (Tian, 2015)
Observationallybaseddata
1) AtmosphericInfraredSounder(AIRS,2003-2010)
2) ERA-InterimReanalysis(1980-2005)
3) NCEP/NCARReanalysis1(1980-2005)
• Climatologicalannualmeanmid-troposphericspecifichumidityrelativebias• (model– observation)/observation(in%)• SHtropicalPacific(120°E-80°W,30°S-0°)– NHtropicalPacific(120°E-80°W,0°-
20°N)
NH tropical PacificSH tropical Pacific
Tropical Pacific
3.8 K
3.3 K
Tropical mid-tropospheric humidity asymmetry index (Tian, 2015)
Lower tropospheric mixing index (LTMI) (Sherwood et al., 2014)
Observationallybaseddata
1) ERA-InterimReanalysis(1980-2005)2) NCEP/NCARReanalysis1(1980-2005)
• Averagedovertropicaloceanregionofmeanascent(upper25%)• Small-scalemixingS=(DR700-850/100%- DT700-850/9K)/2• Large-scalecomponentofmixing=ratioofshallowtodeepoverturning
D=áDH(D)H(-w1)ñ /á-w2H(-w2)ñ• LowertroposphericmixingindexLTMI=S+D
Tropical region of mean ascent (ERA-Interim)
Lower tropospheric mixing index (LTMI) (Sherwood et al., 2014)
3.6 K
2.9 K
NCEP
ERA-Interim
Covariance of tropical low cloud (TLC) shortwave reflection with SST (Brient and Schneider, 2016)
Observationallybaseddata
1) Relativehumidity:ERA-InterimReanalysis,NCEP/NCARReanalysis1
2) TOAradiativefluxes:CERES,SRB,ISCCP-FD
3) SST:HadISST
• MeanoverTLCregions:25%oftropicaloceanarea(30°S-30°N)withlowest500hPa relativehumidity
• TLCreflection(atTOA)=- áScñ /áIñ (in%)• Regressioncoefficients:deseasonalized variationsofTLCshortwave
reflectionandseasurfacetemperature(in%perK)
Annual mean TLC regions (ERA-Interim)
Covariance of tropical low cloud (TLC) shortwave reflection with SST (Brient and Schneider, 2016)
3.7 K
3.3 K
ERAISCCP
HadISST
NCEPSRBHadISST
CMIP5
CMIP3
Southern Hemisphere Hadley cell extent (Lipat et al., 2017)
~3.0 K
ERANCEP
CMIP5
CMIP3
Conclusions and outlook• Allfourofthetestedemergentconstraintsare
sensitivetothemodelensembleand/ortheobservationaldatasets used
• EstimatedECSrangeintheoriginalfourstudies:3.8– 4.0K(2.4– 4.3K)
• Robustnessestimatesobtainedhere(additionalobservationsandensembles):2.9K– 4.1K
• Applyingcompilationofcurrentemergentconstraintstudies(forECS)donotallowtonarrowrangeofECSsignificantly
Outlook• Furtherselectionbasedonphysicalmechanisms andfundamentalprocesses• Focusonindividualfeedbacks toconstrainECS/TCR/TCRE(e.g.carboncycle)• Accountingforobservationaluncertainties• Investigationofadditionalpublishedemergentconstraints• Developmentofnewemergentconstraints
Emergentconstraint Originalrange Thisstudy
ITCZ bias 4.1 K 2.7– 4.1K
Humidityasymmetryindex
3.8K 3.3– 3.8K
LTMI 4.0K(3.0– ) 2.9– 3.6 K
TLCreflection 4.0K(2.4– 4.3K) 3.3– 3.7K