AR4 2050s ensemble scenarios

Previously, due primarily to the difficulty in obtaining data, storing large data volumes and programming requirements, the ensemble approach has been overwhelming. Alternate methods included the use of a restricted set of model projections (two or three models), or the selection of scenarios from this small set which attempted to 'bound' projected climate variables (e.g., 'warm and dry, warm and wet, warmer and dry, warmer and wet'). Although a good approach, this technique still remains limited to a small sub-set of available models.

The current page provides an ensemble projection for all available GCM models outlined previously which have provided their data to the International Panel on Climate Change (IPCC) data warehouse or Program for Climate Model Diagnosis and Intercomparison (PCMDI). Even with these valuable resources, the retrieval of this data in its native format and subsequent conversion, formatting, interpretation, analysis and mapping is a large task not possible for many end-users and stakeholders (local government to the public). The CCDS has provided individual model results for some years now via the climate-scenarios.canada.ca website. This page provides stakeholders with the preliminary results of ensemble change fields for these models for the future commonly cited '2050s' period mean from a common baseline period mean.

The mean monthly temperature and precipitation values are calculated for each model for the periods of 1961-1990 and 2050s (2041-2070). The mean grid-cell value is then used for further analysis.

Monthly GCM model output is interpolated to a common grid (National Centers for Environmental Prediction (NCEP) resolution) at 2.5 x 2.5 degrees across Canada. The GCM model ensemble produced does not include the Canadian Regional Climate Model (CRCM). The NCEP grid resolution is shown in Figure 1.

In addition to a more rigorous estimate, the use of an ensemble versus a single or small combination of models can also provide valuable information of the spatial uncertainty of projections across Canada through the range of model results. Grid cells with greater model ranges indicate regions where different model formulations (sub-grid scale parameterization, atmospheric or oceanic circulations) differ, leading to an overall ensemble projection which has greater uncertainty.

A national map indicating the range of results from all models for the 'low' emission scenario for the future 2050s (2041-2070) annual temperature projection period is shown in Figure 2. Temperature is believed to be one of the best modelled variable outputs from GCMs, yet the range in model results can be significant. In general, the models show a greater range of results over Canada's eastern Arctic (>3°C) and especially over the Labrador sea (>5°C). In southern Canada the range of model anomaly results is less than 3°C on an annual basis. Although the ranges seem very large, it is important to consider that they represent the difference between the maximum and minimum mean annual anomaly (change) from all available GCMs.

A less sensitive statistic to model outliers, the standard deviation, for the same combination just stated indicates a similar pattern (See Figure 3). The standard deviation of projected 2050s anomalies from the models over southern Canada is less than 0.7°C, increasing over the eastern Arctic to 1.2°C, and over the Labrador Sea to greater than 1.6°C where the highest value (and hence uncertainty), is found.