Model Selection

Schematic of a climate model. (source: NOAA)

While it is possible to downscale all available General Circulation Model (GCM) datasets, SNAP focuses on five top climate models from each IPCC Assessment Report and Coupled Model Intercomparison Project (CMIP) effort that are most accurate for Alaska and the Arctic.

We offer downscaled projections for each model, as well as for the average of all 5 models. The average of a set of GCMs generally reproduces observed average monthly climate better than any individual model, but the choice of individual models vs. averaging ultimately depends on how the data are being used.

How the models were evaluated

In collaboration with Dr. John Walsh, SNAP evaluated the performance of 15 GCMs used in the Coupled Model Intercomparison Project 3 (CMIP3) and 22 GCMs used in the Coupled Model Intercomparison Project 5 (CMIP5).

For several regions across Alaska and the Arctic, we calculated the degree to which each model’s output aligned with climate data 1958–2000 for:

  • precipitation
  • sea level pressure
  • surface air temperature

Chosen models

The models that performed best over the larger domains tended to be the ones that performed best over Alaska. From this analysis, SNAP selected the five best-performing models from CMIP3 and CMIP5:

CMIP3/AR4Canadian Centre for Climate Modelling and AnalysisGeneral Circulation Model version 3.1 - t47CCCMA-CGCM3.1(T47)
CMIP3/AR4Max Planck Institute for MeteorologyEuropean Centre Hamburg Model 5MPI-ECHAM5/MPI-OM
CMIP3/AR4Geophysical Fluid Dynamics LaboratoryCoupled Climate Model 2.1GFDL-CM2.1
CMIP3/AR4UK Met Office - Hadley CentreCoupled Model 3.0UKMO-HadCM3
CMIP3/AR4Center for Climate System ResearchModel for Interdisciplinary Research on ClimateJAMSTEC-MIROC3.2(medres)
CMIP3/AR45-model averageCalculated as the mean of the above 5 models5modelavg
CMIP5/AR5National Center for Atmospheric ResearchCommunity Earth System Model 4NCAR-CCSM4
CMIP5/AR5NOAA Geophysical Fluid Dynamics LaboratoryCoupled Model 3.0 GFDL-CM3
CMIP5/AR5NASA Goddard Institute for Space StudiesModelE/Russell GISS-E2-R
CMIP5/AR5Institut Pierre-Simon LaplaceIPSL Coupled Model v5A IPSL-CM5A-LR
CMIP5/AR5Meteorological Research InstituteCoupled General Circulation Model v3.0MRI-CGCM3
CMIP5/AR55-model averageCalculated as the mean of the above 5 models5modelavg

For a description of the model selection process, see Walsh JE, Chapman WL, Romanovsky V et al. 2008. Global Climate Model Performance over Alaska and Greenland. Journal of Climate 21 (23): 6156–74.

We acknowledge the World Climate Research Programme’s Working Group on Coupled Modeling, which is responsible for CMIP, and we thank all the climate modeling groups for producing and making available their model output. For CMIP the US Department of Energy's Program for Climate Model Diagnosis and Intercomparison provides coordinating support and leads development of software infrastructure in partnership with the Global Organization for Earth System Science Portals.