Climate Warming

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Observations reveal that the global climate has warmed over the past century (1900 to 1999), and the warming has been accelerating in the past two decades. There is a widely-accepted scientific consensus that this change is largely due to an increase in the atmospheric concentration of CO₂ and other greenhouse gases (GHGs) as a result of human activity. A more detailed introduction to this topic is provided in The Issue of Climate Change.

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Global climate models (GCMs), which are based on the physics of the climate system, attempt to simulate how GHG increases (and other changes to the climate system) may change temperature, precipitation, and other climate variables. GCMs have been developed in a number of countries over the last several decades and are used to simulate both past, and possible future climate change.

According to the projections made with GCMs, the global mean temperature could rise by about 1.4 to 5.8 degrees Celsius by 2100, depending on the model used as well as on the scenarios of GHG emissions and changes in aerosol loadings due to human activity. The projected temperature change is not evenly distributed geographically or seasonally. The Arctic region would experience the greatest warming for the projected time period. There would typically be more warming over land than over oceans, more at higher latitudes than at lower, and more in the winter compared to the summer.

The climate models also project that global annual average precipitation would increase as the century progresses and the climate warms. As well, projected precipitation changes are not evenly distributed geographically or seasonally. Unlike the case for temperature where warming predominates, there are marked regions of decreasing as well as increasing precipitation over both land and ocean. Annual average precipitation generally increases over northern continents, with the increase concentrated in winter. Evapotranspiration also increases in the warmer climate. The increase of evapotranspiration, especially in summer, together with a less robust increase in summer precipitation, or even a decrease in some areas, leads to projections of reduced soil moisture over some continental regions.

This Module

This module includes 18 maps: 12 maps for the globe and 6 maps for Canada. The global maps display changes in temperature and precipitation between the simulated values for the 1975 to 1995 base period, and those for the middle and end of the current century. The simulation was made by the Canadian Centre for Climate Modelling and Analysis (CCCma) of Environment Canada, using the Coupled GCM (CGCM1) developed there. The national maps display changes in temperature and precipitation between the 1961 to 1990 normals, and the simulated values for the middle of this century generated with the CCCma model CGCM2. For both the global and the national maps, values are given for annual mean changes as well as for the changes for the summer and winter seasons.

Both of the simulations are the result of a projected increase in GHGs, which act to warm the climate, together with an increase in sulfate aerosols, which act to cool it (both linked to human activity). These changes portray the middle level scenario of several possible futures as reflected in the IS92a scenario, which was developed by the CCCma in conjunction with the Intergovernmental Panel on Climate Change.

Data Source

The output of the CCCma models is available on a grid of 3.75 degrees in latitude and longitude, which represents a grid cell size of approximately 400 kilometres by 300 kilometres at Canadian latitudes. The global climate change maps were produced by contouring the CGCM1-output provided by the CCCma of Environment Canada. The climate change maps for Canada were generated using finer scale grid data, which was derived based on the CCCma's CGCM2 output. Both the interpolation and map preparation for the national maps were done by Canadian Forest Service, using a multi-step methodology.

Caution in Interpreting the Maps

The climate change maps provided in this module represent only one of a variety of possible scenarios of future climate change. They represent a climate forecast to the extent that the GHG and aerosol changes used are themselves forecasts. Also, although GCMs attempt to represent our current knowledge of the climate system, and the CCCma models are reasonably successful in reproducing the climate evolution of the past century, all GCMs are simplified representations of the complex processes and factors that govern the Earth's climate. Therefore, future climate scenario results must be treated with caution and this is especially the case when results are viewed at smaller local scales. Regional climate models are one approach to "downscaling" the large-scale results from global climate models to more local scales. These models are under active development in Canada and elsewhere.