The impacts of changing climate are already evident in every region of Canada.

Impacts of changing climate on many physical and biological systems, such as ice and snow cover, river, lake and sea levels, and plant and animal distributions, are unequivocal (Table SR-2) and have been documented in other recent climate change assessments (Intergovernmental Panel on Climate Change 2001, 2007; Arctic Climate Impact Assessment, 2005). In addition, increases in the occurrence of heat waves, forest fires, storm-surge flooding, coastal erosion and other climate-related hazards are consistent with observed climate trends. Many of these impacts directly influence human systems. For example, decreases in the thickness and duration of lake and river ice have significantly impacted the viability of many winter road networks that provide access to remote communities and mine sites in northern Canada (including the northern parts of many provinces; Chapters 3, 5, 6 and 7), while coastal erosion has impacted buildings and critical infrastructure, and threatened cultural sites on all of Canada's marine coasts (Chapters 3, 4, 5 and 8).

There is also strong evidence that climate change has been a contributing factor to a number of other environmental, social and economic issues. These include the unprecedented outbreak of mountain pine beetle in British Columbia, which encompassed over 9.2 million ha of forest in 2007. Although fire suppression and other historical factors have contributed to this outbreak, the recent predominance of hot summers that favour beetle reproduction, and mild winters that allow their offspring to survive, have been critical factors (Chapter 8). Since 1990 in parts of Atlantic Canada, sea lettuce has been spreading, rendering estuaries less suitable for shellfish or finfish and less attractive to residents and tourists. This spread has been related, in part, to climate-driven reductions in freshwater inflow during summer (Chapter 4).

Climate change will exacerbate many current climate risks, and present new risks and opportunities, with significant implications for communities, industry, infrastructure and ecosystems.

Climate change is evidenced by changes in average conditions as well as by changes in climate variability and extreme climate events. Many of the most severe and costly impacts will be associated with projected increases in the frequency and magnitude of extreme climate events and associated natural disasters, including flooding due to high-intensity rainfall and storm surges, ice and wind storms, heat waves and drought (Chapters 2–9). An understanding of future climate extremes is particularly important for the design and maintenance of infrastructure, emergency management, and community health and safety (Chapters 5 and 6).

Gradual changes in average temperature, precipitation, and sea level also affect community and ecosystem sustainability. Some of the most significant and pervasive impacts in Canada will be related to water resources. Water-stressed areas will expand due to decreased runoff in many areas resulting from changes in precipitation and increased evapotranspiration (Chapter 2), while reduced water quality and quantity will be experienced on a seasonal basis in every region of Canada (Chapters 3–8). Increasing demands on water resources for agriculture, energy production, communities and recreation will have to be managed in consideration of ecosystem needs (Chapters 4–8). In addition to increasing the impacts already observed, changing climate will bring new risks to some areas, such as the introduction of vector-borne diseases into areas where climate conditions presently inhibit survival of the vector host (Chapters 5, 6 and 9). Climate-related impacts on ecosystems will present new challenges to the management of protected areas (Chapters 6, 7, 8).

Climate change will also bring opportunities, including longer and warmer growing seasons, which could increase productivity and allow cultivation of new and potentially more profitable crops and tree species (Chapters 4–8). Although global-scale analysis suggests that climate change should benefit Canadian agriculture and forests, studies in Canada that factor in changes in disturbance regimes and more frequent drought are less optimistic and stress the need for timely and effective adaptation (Chapters 7 and 8). Decreased sea-, river- and lake-ice cover permit longer shipping seasons, although lower lake and river levels could have negative impacts on transportation (Chapters 3, 4 and 6). Increased marine transport in the Arctic would provide opportunities for economic growth, along with environmental and security risks (Chapter 3).

Impacts will be cumulative and frequently synergistic. For example, increased frequency and magnitude of heat waves will result in increased peak electricity demand for air conditioning, while decreased runoff from mountain glaciers in western Canada and lower water levels on the Great Lakes are likely to reduce potential for hydroelectricity generation in these areas. Combined with anticipated increases in demand for electricity related to population and economic growth, changing climate could result in increased numbers of black-out and brown-out events (Chapters 6 and 8). The cumulative nature of impacts, and associated cascading uncertainties, makes it likely that climate change will produce 'surprises' — impacts related to the crossing of critical thresholds that have not been anticipated. As is the case for all human and managed natural systems, the magnitude of impacts can be reduced through adaptation.

Climate change impacts elsewhere in the world, and adaptation measures taken to address these, will affect Canadian consumers, the competitiveness of some Canadian industries, and Canadian activities related to international development, aid and peace keeping.

figure SR-4: See text version

Figure SR-4: The number of climate related disasters, by event, from 1950 to 2006 (Munich Reinsurance, 2006).

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Climate change impacts elsewhere in the world will affect supply-demand dynamics and the competitive advantage of some Canadian industries. This will influence the net economic costs of climate change in Canada. For example, although forest productivity may increase in Canada, greater productivity increases in other countries could result in lower forestry-product prices on the global market and a reduced share of the market for Canadian producers (Chapter 9). For tourism, climate change may reduce the attractiveness of some Canadian natural areas (Chapters 3, 4, 5, 7 and 8). When examined in a global context, however, tourism in Canada is expected to be positively impacted by climate change, as warmer temperatures would make Canada a more attractive destination for foreign tourists and encourage more Canadians to forgo vacations to tropical locations due to less severe winters in Canada (Chapter. 9).

Climate changes elsewhere in the world will also influence Canadian humanitarian and development activities. In addition to commitments to assist developing countries in their efforts to adapt to climate change, changing climate will increase the need for disaster relief. Observed trends toward increases in the frequency of extreme climate events (Figure SR-4) are expected to continue in the future. Extreme events are also expected to become more intense. Environmental stress and scarcity issues (primarily related to food and water) caused by climate changes can exacerbate political, social, economic, ethnic, religious or territorial conflicts, leading to increased political instability and displacement of populations (Chapter 9).