Climate scenarios are used to project how climate may change in the future. These projections are not predictions of what will happen, but instead represent one of any number of plausible futures. Current projections, as summarized in the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), suggest that global average temperature could rise by 1.4-5.8°C between 1990 and 2100 (Figure 3; reference 3).

Figure 3: Projected temperature increases for different scenarios, within the context of 1 000 years of historic record (from reference 8). larger image [JPEG, 117.6 kb, 893 X 909, notice]

Due to our northern latitude and large landmass, Canada is projected to experience greater rates of warming than many other regions of the world - by some estimates, more than double the global average. Changes in climate would be variable across the country, with the Arctic and the southern and central Prairies projected to warm the most (Figure 4).

Figure 4: Annual temperature projection for 2080s, based on Canadian Global Coupled Model 2-A21. Image courtesy of Canadian Institute of Climate Studies. larger image [JPEG, 82.6 kb, 800 X 438, notice]

Although the uncertainty associated with projecting future changes in precipitation is greater than for temperature, average annual precipitation is generally expected to increase and changes in precipitation patterns are likely. For instance, heavy precipitation events are expected to become more frequent, and there are likely to be larger year-to-year variations in precipitation.⁽⁵⁾ Seasonal differences will also be important, as most models suggest that there will be less precipitation during the summer months, but increased winter precipitation over most of Canada (Figure 5). Seasonal changes in precipitation patterns are expected to be more important than changes in annual totals in terms of impacting human activities and ecosystems.

Figure 5: Precipitation change, based on Canadian Global Coupled Model 2-A21, for the period 2070-2099 in a) summer and b) winter. Image courtesy of Canadian Institute of Climate Studies. larger image [JPEG, 95.1 kb, 800 X 443, notice]

The probability of extreme climate events will also change in the future. Such changes would occur whether there is a shift in mean values (e.g., such as is projected for annual temperature), a change in climatic variability, or both (Figure 6).⁽⁹⁾ Increases in the frequency of extreme climate events are one of the greatest concerns associated with climate change. Such extreme events include heat waves, droughts, floods and storms. Recent losses from the 1998 ice storm and the 1996 Saguenay River flood are testament to Canada's vulnerability to such events (see Box 1).

Figure 6: Changes in climate mean values and variability will increase the frequency of climatic extremes (from reference 9)

A Range of Impacts

There is increasing evidence that climate change is already affecting human and natural systems around the world. In Canada, this is most evident in the North, where changes in ice cover, permafrost stability and wildlife distribution are impacting traditional ways of life.⁽¹¹⁾ For example, changes in sea-ice distribution and extent have made travel in the North more difficult and dangerous, and have affected access to hunting grounds.⁽¹²⁾ In other regions of Canada, changes in water flows, fish populations, tree distribution, forest fires, drought, and agricultural and forestry pests have been associated with recent warming (see 'Water Resources', 'Fisheries', 'Agriculture' and 'Forestry' chapters).

Box 1: Two disasters of the late 1990s (from reference 10)

Continued climate change, as projected by climate models, would impact all areas of the country and nearly every sector of the Canadian economy. Although a gradual increase in temperature could bring some benefits for Canada (e.g., longer growing seasons and fewer deaths from extreme cold), it would also present challenges. For example, higher temperatures could increase damage from disturbances, such as forest fires and pests (Figure 7), and increase heat-related morbidity and mortality. An increase in the frequency and/or intensity of extreme climate events would have the most serious negative impacts. Experience indicates that natural disasters, such as drought, flooding and severe storms, often exceed our ability to cope, resulting in significant social and economic impacts.

Figure 7: An increase in temperature and drought conditions in the Prairies, as projected by climate models, could lead to more intense and widespread grasshopper infestations in the future. Image courtesy of D. Johnson.