Multi-Model Ensembles Multi-Model Ensembles for Climate Attributionfor Climate Attribution

Arun KumarArun KumarClimate Prediction CenterClimate Prediction Center

NCEP/NOAANCEP/NOAA

Acknowledgements: Bhaskar Jha; Marty Hoerling; Acknowledgements: Bhaskar Jha; Marty Hoerling; Ming Ji & OGP; Participants in the Seasonal Ming Ji & OGP; Participants in the Seasonal

Diagnostics ConsortiumDiagnostics Consortium

What is Attribution?What is Attribution?

Attribution: ascribe to or regard as Attribution: ascribe to or regard as the effect of (a stated causethe effect of (a stated cause) (e.g., ) (e.g., the delays were attributed to the the delays were attributed to the heavy trafficheavy traffic).).

In the context of the observed In the context of the observed climate, “attribution” refers to: can climate, “attribution” refers to: can we relate observed climate we relate observed climate anomalies to external forcing(s)?anomalies to external forcing(s)?

Atmospheric anomalies Atmospheric anomalies Sea Sea Surface Temperatures; Soil Moisture; Surface Temperatures; Soil Moisture; ……OROR a manifestation of variability a manifestation of variability internal to the atmosphereinternal to the atmosphere

Trends in the ocean-atmosphere Trends in the ocean-atmosphere systemsystem changes in solar forcing; changes in solar forcing; aerosols; COaerosols; CO2…2…OROR are intrinsic to the are intrinsic to the coupled systemcoupled system

200-mb Z

SST

Why is Attribution Relevant?Why is Attribution Relevant?

Helps in understanding what the dominant Helps in understanding what the dominant forcing mechanisms controlling climate forcing mechanisms controlling climate variability arevariability are

Provides an understanding of why climate Provides an understanding of why climate is evolving the way it isis evolving the way it is

Provides a basis for making long-range Provides a basis for making long-range predictions and projectionspredictions and projections

An Approach to Attribution An Approach to Attribution AnalysisAnalysis

Analysis of observed anomalies Analysis of observed anomalies (atmosphere, ocean, solar,…)(atmosphere, ocean, solar,…)

Conceptual separation of system into Conceptual separation of system into internal and external (or forced and internal and external (or forced and forcing) componentsforcing) components

Formulation of hypothesis Formulation of hypothesis (e.g. such and such (e.g. such and such anomaly may be because of such and such forcing…)anomaly may be because of such and such forcing…)

Testing the hypothesis involves analyzing Testing the hypothesis involves analyzing response to the external forcingresponse to the external forcing• Empirical approachEmpirical approach• General circulation model approachGeneral circulation model approach

DJF 1997/98

200-mb Z

Model

OBS

DJF 2001/02

200-mb Z

Model

OBS

Problems with attribution based on Problems with attribution based on a single AGCMa single AGCM

In the AGCM approach, attribution In the AGCM approach, attribution keys on the comparison of the keys on the comparison of the observed anomalies with the AGCMs observed anomalies with the AGCMs response to the external forcingresponse to the external forcing

Is the AGCM response to an external Is the AGCM response to an external forcing correct?forcing correct?

One possible solution is to One possible solution is to

• Use Multi-model approach as a “confidence (or Use Multi-model approach as a “confidence (or consensus) builder” in documenting response consensus) builder” in documenting response to an external factorto an external factor

• Once a level of confidence could be placed in Once a level of confidence could be placed in the atmospheric response to the external the atmospheric response to the external forcing, more definite statements about the forcing, more definite statements about the causality of observed anomalies can be madecausality of observed anomalies can be made

DJF 1997/98

DJF 2001/02

Seasonal Diagnostics Seasonal Diagnostics ConsortiumConsortium

ModelModel CCM3CCM3 NCEPNCEP NSIPPNSIPP ECHAM4.5ECHAM4.5

(From IRI) (From IRI)

GFDLGFDL

TypeType SpectralSpectral SpectralSpectral GridGrid SpectralSpectral GridGrid

ResolutionResolution T40L18T40L18 T62L64T62L64 2 Deg2 Deg

Lat/LonLat/Lon

T40L18T40L18 N45L18N45L18

# of# of

SimulationsSimulations 2020 1818 99 2424 1010

Total # of Simulations : 81

2004 EOS2004 EOS

2004 EOS2004 EOS

Add the line plotAdd the line plot

MM Climate AttributionMM Climate Attribution

Other Application of MM attribution runsOther Application of MM attribution runs

• Documenting atmospheric responses to Documenting atmospheric responses to boundary forcingsboundary forcings

• Inferring current state of climateInferring current state of climate• Analyzing successes and failures of operational Analyzing successes and failures of operational

SI forecastsSI forecasts• Generating different SI prediction scenariosGenerating different SI prediction scenarios• Model validation Model validation (has long been the implicit basis for (has long been the implicit basis for

various MIP activities)various MIP activities)

Atmospheric Response to SST Atmospheric Response to SST ForcingForcing

(2000-2004) - (1961-90)

Atmospheric Climate Model Simulations Observed SST Forcing Institution Model Ensemble Size GFDL AM-2 10 MPI/IRI ECHAM-4 24 NASA GMAO 23

Simulation production for 1950-2004 Specified monthly varying global SSTs Climatological GHG/Aerosols 57 member multi-model ensemble Experiments are part of Seasonal Climate Diagnostics Consortium http://www.cpc.ncep.noaa.gov/products/people/bjha/

(2000-2004) - (1961-90)

Atmospheric Climate Model Simulations Idealized Indian Ocean SST Forcing Institution Model Ensemble Size GFDL AM-2 10 NCEP GFS 10 NCAR CCM3 10 NCAR CAM3 10 Transient +0.1°C/yr Indian Ocean warming Each run is 11-yrs in duration. Climatological SSTs elsewhere. Climatological GHG/Aerosols 40 member multi-model ensemble http://www.cgd.ucar.edu/cas/asphilli/Results/Ramped-IndianOcean/

Inferring Current State of Inferring Current State of Climate Climate (consistent with the external forcing)(consistent with the external forcing)

Response Forced by the Observed

SSTs

Coupled Ocn-Atm Climate Model Simulations Observed GHG/Aerosol Forcing Simulation production for 1895-2004 Specified monthly varying GHG/Aerosol 1895-2000 A1B Scenario 2001-2004 18 Different Coupled Models/47 total runs Experiments are part of the IPCC AR-4 Suite http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php

Land Temp

SSTs

(2000-2004) - (1961-90)

Validating ForecastsValidating Forecasts

NDJFM 2004/2005

Efforts in NOAAEfforts in NOAA

What currently exists: An informal activity What currently exists: An informal activity maintaining monthly updates in AMIP runs maintaining monthly updates in AMIP runs forced by Global SSTsforced by Global SSTs

Within NOAA, need to formalize attribution Within NOAA, need to formalize attribution activity for different time scales [could be activity for different time scales [could be centralized or a virtual activity]centralized or a virtual activity]

Such an activity can also support other Such an activity can also support other model based “hypothesis testing” efforts model based “hypothesis testing” efforts (e.g., impact of different ocean basins; (e.g., impact of different ocean basins; causality of trends and droughts; …)causality of trends and droughts; …)

June 1998-May 2002(The Perfect Oceans for Drought)

OBS

MODEL