Climate models and scenarios: Tools to glimpse the future
The scientific understanding and projection of anticipated changes in our future climate (and its associated variability) is a rapidly evolving research field. Nonetheless, a clear picture of the expected changes in global climate is emerging, and there is increasing confidence in the prediction of climate trends at the regional level. Climate models are the primary tools used to assess future climate.
Climate models are computer programs that simulate the climate system’s behaviour based on the fundamental laws of physics. Although they are the best available representation of the planet’s climate, they are only a simplified version of natural processes. There are two types of models: global climate models (GCMs), which simulate coarse planet climate dynamics with a horizontal spatial resolution of 250 kilometres (km) × 250 km, and regional climate models (RCMs), which cover a limited area with a finer resolution of approximately 50 km × 50 km.
Figures 1 and 2 provide examples of the type of information on future climate that can be accessed through the Canadian Climate Change Scenarios Network (CCCSN). These figures show mean differences in annual temperature and precipitation patterns of the future period (2041–2070 – a.k.a. 2050s) compared with the historical period (1961–1990). The figures are an ensemble of two versions (4.2.0 and 4.2.3) of the Canadian Regional Climate Model (CRCM), with boundary conditions established by output of the third generation of the Canadian Global Coupled Circulation Model. The output from the two versions are averaged during the historical period and again for the future period. The differences between the two periods are presented in the figures. The future projections are based on a high-level of global socio-economic growth and no change in the relative consumption of renewable versus non-renewable energy resources (SRES-A2 scenario, IPCC 2000).
Figures 1 and 2 represent only one possible future Canadian climate as analysed by the CRCM. Simulations from other RCMs, which may use different nesting data (GCMs), different time periods or different greenhouse gas emission scenarios, will produce different results from those shown here. Also, each climate model contains inherent uncertainties related to the hypotheses and the simplifications of the real world on which it is based. Consequently, municipal governments are strongly encouraged to use several climate models and scenarios to evaluate and compare climate change outcomes for their region. An “ensemble approach,” in which the projections from many models are averaged, is useful because individual model biases are removed. The CCCSN recently produced an ensemble projection of seasonal temperature and precipitation change across Canada by using all available GCMs from the Intergovernmental Panel on Climate Change’s Fourth Assessment Report (IPCC 2007).
Climate models are not yet at the spatial and temporal scales of resolution that correspond to many extreme weather events such as thunderstorms and extreme rainfall. Note also that changes in average seasonal rainfall are insufficient to assess changes in drought or flood conditions for a specific area.
Climate models provide the virtual meteorological data that feed into the construction of climate scenarios. Climate models and climate scenarios are part of a suite of tools that can be used to determine likely impacts of climate changes for a region.