The four AOGCMs we chose for providing boundary conditions for the RCMs are: the Canadian Global Climate Model version 3 (CGCM3, T47 spatial resolution, [Flato 2005]); the NCAR Community Climate Model version 3 (CCSM3, [Collins 2006]); the Geophysical Fluid Dynamics Laboratory (GFDL) Climate Model version 2.1 (CM2.1, [GFDL 2004]); and the United Kingdom (UK) Hadley Centre Climate Model version 3 (HadCM3, [Gordon 2000], [Pope 2000]). Table 1, below, provides the major characteristics of each model. More on these models and their evaluation can also be found in Randall et al., 2007, in the references cited for the individual models, and at the PCMDI web site where the global model output is stored.

All four models and modeling groups have participated in all IPCC exercises with global climate models and have well established track records for simulating current and future climates. The equilibrium climate sensitivities of the four models are: 3.4° C, 2.7° C, 3.4° C, and 3.3° C, respectively. The full range of climate sensitivity for the models that participated in IPCC 2007 is 2.1°C–4.4° C. Equilibrium climate sensitivity is defined as the global mean temperature response of an atmospheric climate model run with a simple (slab) ocean to a doubling of CO₂. It is a measure of the climate system annual mean temperature change in response to a doubling of CO₂ after it has attained equilibrium [Randall 2007]. Climate model sensitivity is one of the factors that results in the range of climate change projections obtained with different AOGCMs. It is now believed that the most likely value for climate sensitivity is around 3.0°C [Meehl 2007], and the values for the AOGCMs we are using bracket this value.

Table 1. Characteristics of the 4 AOGCMs used to provide boundary conditions for the RCMs (adapted from [Randall 2007]). L is the number of vertical layers; degrees (°) refer to latitude and longitude; top refers to the pressure at the highest model atmospheric vertical level; rheology refers to the flow (material) characteristics of sea ice (modeled as a viscous plastic); free drifts refers to modeling of ice movement such that ice drifts freely with the ocean currents; leads refers to characteristics of the ice leads i.e., the fact that the model includes ice free portions within the pack ice; routing indicates where there is river routing prescribed in the land surface model; layers or bucket indicates how the soil layers are modeled; canopy indicates that a full vegetation canopy is simulated in the land surface model.

The four AOGCM simulations that were chosen to provide boundary conditions for the regional climate models all were generated using the A2 emissions scenario. The results of the AOGCM simulations are available at PCMDI at http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php. This data set contains output from the AOGCM simulations produced for the IPCC 2007 report.

The realizations of each AOGCM used for NARCCAP are as follows:

*We are working on publishing the full boundary condition data through ESG, but at the moment only monthly and seasonal averages are available here.

References

Collins, W. D., et al., 2006: The Community Climate System Model: CCSM3. J. Climate 19:2122-2143.

Flato, G. M., 2005: The third generation coupled global climate model (CGCM3).
http://www.ec.gc.ca/ccmac-cccma/default.asp?n=1299529F-1

GFDL GAMDT (The GFDL Global Model Development Team), 2004: The new GFDL global atmospheric and land model AM2-LM2: Evaluation with prescribed SST simulations. J. Climate 17:4641-4673.

Gordon et al., 2000: The simulation of SST, sea ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments. Climate Dynamics 16:147-168.

Pope et al., 2000: The impact of new physical parameterizations in the Hadley Centre climate model: HadAM3. Climate Dynamics 16:123-146.

Meehl, G. A., 2007: Global climate projections. In: Climate Change 2007: The Physical Basis. (Solomon et al., eds.) Cambridge University Press:Cambridge. pp. 747-845.

Randall, D.A., et al., 2007: Climate models and their evaluation. In: Climate Change 2007: The Physical Basis. (Solomon et al., eds.) Cambridge University Press:Cambridge. pp. 589-662.