Multi-model ensemble scenarios
Projections among climate models can vary because of differences in their underlying representation of earth system processes. Thus, the use of a multi-model ensemble approach has been demonstrated in recent scientific literature to likely provide better projected climate change information.
Given the range of natural climate variability and uncertainties regarding future greenhouse gas emission pathways and climate response, changes projected by one climate model should not be used in isolation. Rather, it is good practice to consider a range of projections from multiple climate models (ensembles) and emission scenarios.
While likelihoods are not associated with particular climate change scenarios, the use of a range of scenarios may help convey to users the potential spread across a range of possible emission pathways.
CMIP5 multi-model ensemble on CCDS
A new feature of the IPCC Fifth Assessment Report (AR5) is the Atlas of Global and Regional Climate Projections (Annex 1--IPCC, 2013), which provides a synthesis of results from the Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model ensemble.
For application to Canadian impact studies and adaptation planning, the regional boundaries of the Atlas are less than optimal: western Canada is combined with the western United States and Alaska, and eastern Canada is combined with Greenland and Iceland (but separated from western Canada).
Therefore, CCDS includes multi-model ensemble results generated specific to Canada, using output from 29 CMIP5 models from which results were available for historical simulations and three representative concentration pathways, RCP2.6, RCP4.5, and RCP8.5. Results for RCP6.0 are also available, but from fewer models, so this scenario is not included for multi-model results presented on CCDS.
For further details on the models used in the 29 CMIP5 ensemble, please see CMIP5 technical notes.