Meteorological Service of Canada (MSC)

Understanding Atmospheric Change

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Chapter 5 - A warmer Canada

Canadian scientists working under the co-ordination of the Canadian Climate Program are investigating the possible environmental, social, and economic effects of climate change in Canada. As a basis for their analyses, projections from several GCM experiments have been used to indicate how the general characteristics of the climate might change. Historical climate data, factored into these projections, provide further information about how day-to-day weather patterns might be affected and make it possible to calculate the likely frequency of extreme weather events, such as hot or cold spells and wet or dry periods. The material in this chapter is based on recent studies of this kind.

Canada's forests

Much of Canada is covered by trees, from the black spruce and birches of the cold boreal forests to the pine and hardwoods of the warmer and more humid southern latitudes. The two regions that remain treeless do so partly for climatic reasons-the Prairie grasslands because of low soil humidity and the northern tundra because of low temperatures.

Given the extent of this resource, it is not surprising that forestry is Canada's largest industry. Companies involved in the harvesting and processing of wood products in this country generate revenues in excess of $45 billion and employ more than 280 000 people. Forests are also of major importance from an ecological perspective. They constitute vital habitats for wildlife, significantly affect the hydrological and radiative processes of the climate system, and form a major part of the global reservoir of living carbon. Hence, their future health is important not only to Canada's economic well-being but also to the elemental processes of the biosphere.

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In general, the combined effects of higher carbon dioxide concentrations, longer and warmer growing seasons, and milder winters should bring a major improvement in the productivity of forests in many areas of Canada. Under the type of climate expected for the middle of the next century, for example, Quebec's forests could increase their annual yields by anywhere from 50% to 100%. However, the boundaries of the different forest types will undergo radical alterations (Figure 25). These shifts will decrease the total area in Canada covered by trees, with most of the losses occurring as Prairie grasslands expand northward and eastward, in step with reductions in available soil moisture.

The largest changes would occur in the area now covered by boreal forests. At the southeastern edges of these forests, the dominant black spruce would gradually yield to the encroachment of the evergreens and hardwoods of the cool temperate forests. Meanwhile, at the northern margins of the boreal forest, expansion into tundra regions would be greatly delayed by poor soils and the comparatively slow decay of the underlying permafrost.

Just how disruptive these changes may be will depend to a considerable extent on how quickly they occur. Canada's temperature patterns can be expected to shift northward by about 100 km for every 1°C of warming. However, in responding to changes in climate, many tree species migrate slowly, at rates of 700 m or less a year. Consequently, a smooth transition from one forest type to another, with retreating species being replaced quickly by advancing species, will occur only if the pace of climatic change is very gradual. Even then, the transition from one forest type to another will be sporadic and uneven, since forest fires are a key element in the replacement of existing tree species with new ones. Unfortunately, climate models suggest that temperature and precipitation values will change quickly. If so, the consequences are likely to be severe, particularly along the southern and low soil-moisture limits of each species.

Where trees are exposed to additional stresses, such as acid rain, ground-level ozone pollution, increased ultraviolet radiation, or leaching of harmful chemicals from the soil, forest destruction could occur on a large scale. Recent diebacks of maple stands in Ontario and Quebec may be symptomatic of such changes.

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Warmer climates will also bring with them the danger of increased insect and disease infestation, as pests and diseases once alien to our forests migrate northwards. In addition, the accumulation of greater amounts of dead biomass, together with drier summer conditions, could cause large increases in the frequency and severity of forest fires. In fact, such increases have already occurred during the warm, dry years of the 1980s and 1990s (Figure 26). Finally, the destruction of forest cover will result in more carbon dioxide being added to the atmosphere, thus further enhancing global warming.

Agriculture

Canada's agricultural potential is limited by, among other things, its cold climate. With the length of frost-free growing seasons restricted to between about 200 days in the extreme south and merely a matter of weeks in the far north, Canadian soils remain inactive for a major part of each year. Furthermore, severe winters can cause frost damage even to dormant vegetation, thus restricting the cultivation of overwintering crops, such as winter wheat, on the Prairies and in other similarly affected areas. When growing seasons do arrive, growth rates of plants in Canadian climates are further restricted by the amount of heat energy available to them during the season. These factors impose major limitations on the types of crops that can be grown in Canada, as well as on the yields and the number of crops that can be harvested in one year.

It would seem, therefore, that warmer temperatures would be very good for Canada's agriculture. For example, under typical climate scenarios for 2050 AD, growing seasons around Whitehorse and Yellowknife would be similar to those in the Edmonton area today, while conditions in New Brunswick would resemble those of the Niagara peninsula.

The growth potential of vegetation in regions such as southern Quebec, central Ontario, and southern Saskatchewan could improve by 40-50%, assuming that all other variables, such as soil moisture and pest infestation, remain constant. Hence, there would be considerable potential for cultivating higher-yield crops requiring a longer and warmer growing season, for increased multicropping in more southerly latitudes, and for the expansion of frontier agriculture northward. Grain corn could become an important agricultural crop in areas such as Manitoba and northern Ontario, winter wheat would do well on the Prairies, and apples and grapes could become highly productive in Quebec. The nutritional effects of higher carbon dioxide concentrations would further add to these benefits, perhaps enhancing productivity by 15% or more.

There would be advantages for livestock production as well. Warmer temperatures would allow longer forage periods and reduce the need for supplemental feeding.

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Unfortunately, other variables will not remain constant or unrestrictive. In the first place, the availability of soils suitable for agriculture in Canada is limited. At the present time, only about 10 million hectares of potential agricultural land in Canada are currently unutilized because of climate constraints (Figure 27), and much of this land consists of marginal soils that are unsuitable for cereal grain production. Furthermore, some areas that do have suitable soils are covered with valuable timber stands. Consequently, the potential for expanding agriculture into the northern frontier is not large.

Secondly, because insects, pests, and plant diseases are responsive to climatic shifts, the probability of severe infestations in future decades is increased. Many crops are also sensitive to heat stress, particularly during key stages of development, and may be adversely affected by the increased frequency and severity of summer heat waves. Dairy cows are vulnerable to heat stress as well, and unless farm operations were modified to reduce the stress, milk production would decline.

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Finally, higher temperatures will significantly increase the rate at which vegetation and soils lose water to the atmosphere, thus reducing available soil moisture. In areas where rainfall increases significantly during the growing season, this loss will normally be replenished. However, drought studies suggest that even under such conditions, drought years that occur everywhere as part of natural year-to-year climate variability will become more frequent and more severe (Figure 28).

In areas where rainfall is projected to remain constant or decrease, significant increases in drought frequency and severity will cause major crop stress and economic hardship. Many of Canada's key agricultural regions, including the Prairies, southern Ontario, and southern Quebec, could experience such conditions. In fact, the 1988 growing season in Canada, which witnessed large crop losses through most of these regions due to major drought stress, provides a very useful example of how the average summer climates of Canada may appear in the future. While such events are not unprecedented in Canada's history, they are likely to occur more frequently during the decades to come.

Water resources

Although climate models disagree on the future distribution of rain and snow amounts across Canada, they do agree on the following points:

• During the winter the quantity of precipitation is likely to increase across Canada.
• The snow season, however, will be significantly shorter. In most areas snow accumulations will be less and spring melts and runoffs will occur earlier, although snow accumulation in northern latitudes could increase significantly.
• During the growing season precipitation amounts are likely to increase in northern Canada and decrease or remain relatively unchanged in southern Canada, as dominant storm tracks push further north.

These changes will have profound effects on our management and use of water resources. From a simple perspective, water runoff from land surfaces to streams and rivers is provided by moisture left over from rain and snowfall after the losses due to evaporation, vegetation needs, and soil saturation are accounted for. Many of our lakes and streams receive a large proportion of their annual water supplies from the melting of snow cover in the spring, when the soil underneath is still frozen, vegetation is still dormant, and evaporation losses are comparatively low. Significant changes in the annual accumulation of snow, the timing of the spring melt, and the rate of evaporation loss from soil and vegetation will therefore dramatically alter the behaviour and conditions of Canada's rivers, lakes, and reservoirs.

Although uncertainty about the nature and extent of local precipitation changes makes it impossible to predict how the water resources of each region of Canada will be specifically affected by climatic change, some useful clues can be drawn from the results of climate modelling experiments. This information suggests that water resources in northern Canada are likely to become more abundant, although the annual spring runoff will likely be smaller and will occur earlier. Such a situation could substantially increase the potential of northern watersheds for hydro-electric production. In northern Quebec, for example, power output could increase by 15% or more.

However, these benefits might be offset to some degree by growing demands for large-scale water diversions to parched regions in the south, where warmer temperatures are likely to bring higher rates of evaporation and increased soil dryness. Drier soils are expected to reduce runoff, in some cases dramatically, causing lower stream flow and lake levels. These effects would be particularly severe during drought years.

Typical scenarios suggest that water levels in the Great Lakes could fall by 0.5 to 1.0 m or more on average, while the amount of water flowing out of the St. Lawrence River could be reduced by up to 20%. Extremely low lake levels, such as those of 1963-65, could occur four out of every five years (Table 3). As well as causing a deterioration in water quality, such changes could also cause shipping costs in the Lakes to rise by as much as 30%, as large vessels would be forced to load more lightly in order to pass through canals and shallow waterways. Total revenue from hydro-electric power generation at southern sites could also fall off by $30-60 million per year. Finally, drier conditions would lead to the disappearance of many ecologically important wetlands, such as those at Point Pelee on the shore of Lake Erie.

Snow and ice

Snow and ice play a major role in Canada's geography, its climate, and its culture. They cover nearly all of Canada's land surfaces and most of its water surfaces for at least part of the year and, in some areas, for the whole year. In the form of permafrost, ice in northern Canada is also a major factor in the drainage of water, in the growth of vegetation, and in land stability. Glaciers and ice caps exert a major influence on regional climates and are major sources for the icebergs that populate the waters off our east coast and the ice islands that travel the Arctic Ocean.

Warmer temperatures and projected increases in winter precipitation will significantly alter these characteristics. In northern regions, snow seasons will likely become much shorter but more intense. The duration of ice cover on lakes and oceans will be shortened by up to several months. Hudson Bay could become largely ice-free all year, while the Arctic Ocean may become virtually ice-free in mid-summer. As a result, Arctic waters would become much more accessible to marine navigation and other offshore activities, including fishing and resource exploitation. On the other hand, scientists suggest that increased snow accumulations on top of the Arctic ice caps and longer and warmer melt seasons at their margins will accelerate glacial flow and increase iceberg calving by as much as 300%.

Meanwhile, gradual decay of the southern edges of the Arctic permafrost will drastically alter surface water drainage patterns and increase the instability of the land. As a result, significant disruptions to pipelines, rail lines, roads, and other facilities could occur. The effect on ice roads could be particularly unfortunate. Built across frozen wetlands and lakes, these roads provide a valuable supply link to many remote communities and give access to large areas of timber in the boreal forest. Under milder conditions, they will be more difficult to construct and won't last as long. Their load-bearing capacity will be reduced too, because of thinner ice. In some areas they could cease to be a reliable means of transportation.

In more southerly latitudes, the reduction of snow and ice cover would have profound effects on several activities. By and large, transportation would benefit, as roads required less snow clearing and waterways became more navigable. The Great Lakes and the Gulf of St. Lawrence would likely become predominantly ice-free year-round, while the multimillion-dollar snow removal budgets for large urban centres such as Montreal and Toronto could be virtually eliminated. However, seasons for traditional winter sports such as skiing, snowmobiling, ice fishing, and outdoor skating would be greatly shortened or, in the case of southern Ontario, might disappear altogether (Table 4). The economic impact on related industries would be considerable.

Coastal flooding

Because of the ruggedness of its coastline, Canada is much less vulnerable to coastal flooding than many other nations. Yet it will not remain unaffected if sea levels rise. Important coastal wetlands such as the Hudson Bay lowlands and the Mackenzie Delta could undergo large-scale flooding. Beaches and shorelines elsewhere will recede and erode.

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However, the largest impacts on Canadians will occur in the populated centres along the Atlantic and British Columbia coasts where large city blocks and shorefront facilities lie close to sea level. As sea levels rise, lower Vancouver and other municipalities on the Fraser River Delta, already confronted by occasional flooding problems, would require large investments in new and improved protective barriers to avoid major inundations. At Charlottetown, a 1-m rise would flood the city's new harbourfront development at high tide, while major storm surges, which occur about once every 20 years, would be high enough to inundate large parts of the downtown residential and commercial districts (Figure 29). In Saint John, N.B., road and rail transportation would be vulnerable to frequent flooding, as would sewage disposal systems and downtown buildings. Other problems would include contamination of water supplies, loss of farmland in rural areas, and increased flooding of rivers upstream of the coast during spring runoff.

Some of these effects could be reduced, or aggravated, by the natural vertical movement of the land. The Hudson Bay region, for example, is still rebounding from the last ice age, and its shoreline is rising at a rate comparable to projected sea level rises due to global warming. The Nova Scotia land mass, on the other hand, is gradually sinking, thus enhancing any water level effects that may result from global warming.

Other effects

Since most social and economic activities are sensitive to weather and climate, the impacts of warmer climates will go well beyond those already mentioned. The following additional effects are of particular significance.

Energy consumption - Requirements for space heating in homes, offices, and factories will be much lower during warmer winters. Such reductions will vary from more than 30% in the warmer climates of southern Canada to about 20% in Canada's cold north, where heating requirements are very high. These benefits will be partially offset in the south by increased requirements for summer cooling. Warm climates would also generally improve the efficiency and, hence, the energy consumption of surface and marine transportation.

Temperature stress - Warmer winters will result in a substantial reduction in the number of very cold spells to be endured each year and in their severity. Summer heat waves, however, will occur more frequently and reach new extremes.

Human health - Heat stress can cause illness or death in the most susceptible segments of the population, especially the very young and the elderly. More frequent heat waves would increase mortality in summer months, especially when the heat is accompanied by the influx of polluted air masses. A warmer climate would allow different species of plants to flourish, changing the amount and types of pollens which could affect allergy sufferers. Presently, many natural disease carriers are unable to survive our cold winters. A reduced cold season may allow some diseases (such as malaria) and insects harmful to ecosystems to extend their range northward into southern Canada.

Fisheries - The types and growth rates of fish and marine life found in freshwater lakes are significantly influenced by seasonal temperature limitations. Because of this, fish populations and species will change across Canada as the climate becomes warmer. In general, the changes will benefit the less-valued dark species, while the higher-quality white species will suffer from decreasing habitats. At the same time, these changes will be complicated by additional stresses from changing water quality and nutrient supplies. In Canada's coastal waters, changes in salinity, temperature, and current flow will all affect the distribution of marine species and their numbers. Warmer climates will likely benefit fish farming.

The effect on offshore fisheries is much more uncertain, since these are largely influenced by ocean currents. However, in the past, ocean warming has brought exotic fish species into the Pacific coastal waters and has had major impacts on the abundance and distribution of cod along Canada's east coast.

International security - The effects of climate change on other regions of the world will have wide-ranging implications for the economic, social, and political security of Canadians. Changes in the global distribution of food production, for example, will alter traditional food trade patterns. Canada, as both a major importer and exporter of food, will have to adapt to the new conditions, finding new sources of supply in some cases and new markets in others.

Meanwhile, chronic food shortages or other disasters arising from climate change in the developing world will place pressure on Canada to provide emergency relief assistance, accept environmental refugees, and perhaps help resolve armed conflicts. Furthermore, while pursuing aggressive and perhaps costly domestic action to reduce their own emissions of greenhouse gases, Canada and other industrialized countries will be expected to transfer financial and technical resources to help developing nations undertake similar action.

Climate change and extreme weather

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In spite of the uncertainties associated with them, GCMs provide a reasonably clear indication of the probable direction of change of the world's average surface climate in the decades to come. However, both humans and ecosystems are much more vulnerable to the occurrence of extreme events such as droughts, floods, heat waves, and cold spells than to gradual shifts in climate. Because of their severity and unpredictability, these events can bring with them hardship, economic loss, severe social disruption, and even loss of life.

Determining the influence of a warmer climate on the frequency and severity of extreme weather events is therefore critical to our understanding of the impact of an enhanced greenhouse effect, but so far climate models have provided few useful insights into the variability of future climates. Some preliminary indications have been obtained, however, by combining the projected average change from climate model studies with detailed climate data from the past 30 years.

Not surprisingly, such an analysis suggests that hot spells in summer will become more frequent and more severe in Canada, while very cold periods in winter will become less frequent (although they will still occur). In Saskatoon, for example, the frequency of July days exceeding 31°C could increase under a doubled-CO₂ climate from the current average of 3 days a year to 8. Conversely, extremely cold January days below -35°C could decrease from the current average of 3 days each year to 1 day every 4 years. Meanwhile, studies into southern Saskatchewan drought frequencies suggest that, even if average conditions were to become moister, severe droughts could become twice as frequent because of higher evaporation.

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