Continental Effects (North America)



Higher temperatures and a changing rainfall regime are affecting water supply, water demand and water quality in Canada, Mexico and the United States. Most of the observed trends of the past 35 years are expected to continue in the coming decades. Two major issues for Canada relate to managing the border and transborder basins shared with the United States (International Joint Commission, 1997) and responding to demands for export of water to the dry regions of the United States and northern Mexico (Bruce et al., 2003).

Canada-United States Border and Transborder Waters

There are a dozen large bilateral drainage basins, or groups of small basins, for which the International Joint Commission (IJC) has responsibility under the Boundary Waters Treaty of 1909. Many of these basins, and their subbasins, have water-sharing agreements where rivers flow north or south across the border or form the border. Also, in some basins, pollution control agreements are in place to protect ecosystems and water quality (e.g. Great Lakes -St. Lawrence River). Climate change is beginning to affect both the quantity and quality of these waters, and the ability of one country to meet its present obligations to the other (Bruce et al., 2003).

To illustrate the potential extent of the issue, Table 4 gives the linear trend (1970 -2000) in annual flows and minimum and maximum flows for major bilateral rivers. Most are downwards except for the Red River, which flows northward from the Dakotas, where significant increases in precipitation have occurred (Bruce et al., 2003). These bilateral stresses are superimposed on domestic water management issues (Cohen et al., 2004).

On the Columbia River, the trend towards greater flow in winter and less flow in spring is expected to continue. Changing water demands in the United States, combined with climate change, could seriously compromise hydroelectric power generation and other uses in Canada, especially in drier regions in southern areas of the Canadian part of the basin (e.g. Okanagan and Osoyoos lakes, see Chapter 8; Cohen et al., 2000; Payne et al., 2004). Existing processes through which rules are being reviewed for possible changes in 2013 provide an opportunity for consideration of adaptation to climate change.

Table 4: Trends (percentage change) in annual flows for boundary river systems between Canada and the United States, 1970-2000 (Bruce et al., 2003).
River Mean Minimum (daily) Maximum (daily)
St. John (Fort Kent) -13 71 -16
St. Croix -21 -23 -26
Niagara (Queenston) -7 -8 -9
Rainy (Fort Frances) -22 -12 -27
Lake of the Woods (western outlet) -21 -59 -29
Red (Emerson) 124 159 63
Souris (Sherwood) -82 -74 -94
Souris (Westhope) -42 100 -60
Milk (eastern border crossing) -22 47 -6
Milk (western border crossing) -26 59 -41
St. Mary (border) -7 15 -29
Kootenay (Fort Steele) 3 -4 -12
Columbia (International Border) 4 37 -25
Yukon 1 -1 -12

The Souris River flows out of Canada into North Dakota at Sherwood, SK, and back into Canada (Manitoba) at Westhorpe, ND. Under a 'normal climate', each country can use 50% of the natural flow up to the border crossing. Natural flow is calculated by a joint board reporting to the IJC, which takes the measured flow and adjusts for human withdrawals and reservoir evaporation upstream. At the Sherwood crossing, Canada is required to deliver half of the first 50 000 cubic decametres (40 500 acre-feet) of natural flow in the January 1 to May 31 period. With the downward trend from 1973 to 1998 in mean annual natural flow from 7 to 2.5 m 3/s, Canada's obligation was not met in 5 years between 1988 and 2000 (Bruce et al., 2003). However, there is a clause in the agreement, which had to be invoked, to provide to North Dakota 40% of the natural flow in the critical period. Continuing and more acute problems with declining flows and increasing consumption for stock watering and irrigation due to climate change are expected to result in frequent inability to meet the initial quantitative goal (Bruce et al., 2003).

There have been serious problems in meeting the provisions of apportionment agreements, established in 1921, for the Milk and St. Mary rivers due to declining flows in southern Alberta and reduction of meltwater from headwaters in Glacier National Park5 in the United States. These trends and increased demand for irrigation reached the point that, in 2003, the Governor of Montana called for reopening of the existing agreements. Bilateral discussions continue with the aid of the IJC.

In the Great Lakes basin, a critical agreement for sharing water is the Niagara River Treaty of 1950. An agreed amount, 100 000 cubic feet per second (cfs) in daytime and 50 000 cfs at night, is allowed to go over Niagara Falls for the benefit of the tourists. The balance is divided equally between Ontario and New York State for hydroelectric power generation. With the upper Great Lakes (Superior, Michigan, Huron) having progressively less ice and higher surface temperatures as the climate warms, winter-time evaporation losses have substantially increased and will continue to do so. This resulted in a 7% decline in the mean annual flow of the Niagara River between 1970 and 2000 (Bruce et al., 2003). Continuation of this decline is expected with climate change, and adjustments to the agreement and/or to operations may be needed (Mortsch et al., 2000; Bruce et al., 2003).

Water quality in the Great Lakes is affected by more intense rains in the watershed, which increase erosion and wash pollutants into the lakes; by higher water temperatures; and by earlier establishment of a thermocline, allowing bottom waters to become depleted of oxygen earlier in the warm season. There are questions as to whether the two countries can achieve their mutually agreed water quality objectives under these changing climate conditions (Great Lakes Water Quality Board, 2003). For example, an increase in the frequency of high-intensity rains, resulting in more erosion and diffuse sources of pollution to the lakes, causes increased problems associated with nutrients, pathogens (e.g. E. coli), turbidity and pesticide products (Bruce et al., 2006).

Although Canada and United States have an enviable record of settling water disputes amicably through the International Joint Commission and the Boundary Waters Treaty, climate change threatens to stress this relationship. In order to adapt to changes already occurring and projected future changes, the management and terms of some of these agreements may need to be adjusted (Bruce et al., 2003).

External Demands for Canadian Water

Although the flow of rivers in the southeastern United States has risen substantially in the past 60 years, flow has decreased in most rivers of the west, especially during the April to autumn period (Frederick and Gleick, 1999; Pulwarty, 2002; Barnett et al., 2005). In snowmelt regions, particularly for rivers fed by snowmelt in their headwaters in the Rocky Mountains, more winter depletion of the snowpack has occurred by melt and sublimation. This has resulted in a marked downward trend (1950 -2000) in April snowpack water equivalent (Mote et al., 2003), and changes in seasonality of water supplies, with more flow in winter and less in the rest of the year. Drier conditions are occurring in the irrigation and stock-watering seasons of summer and fall. The longer term trend since 1900 in the southwestern United States and in Mexico has been an increase in the Palmer Drought Severity Index (Figure 3; Dai et al., 2004).

This change towards drier conditions in the western United States, especially during the growing season, has exacerbated overcommitment of the waters of the Colorado River to users in many states (Gleick and Chalecki, 1999). Seasonal decline in the flows of the Columbia and Sacramento rivers are also sparking conflicts over uses, including instream ecosystem and fish protection (e.g. Cohen et al., 2000). Overpumping of the Ogallala aquifer in Nebraska, Oklahoma and the high plains of Texas has seriously lowered levels and depleted supplies for agricultural and other uses. Conflicts are simmering over the sharing of reduced water in the border and transborder rivers between the United States and Mexico (Salman, 2006).

As a solution for these problems, some have looked to the north, to the apparently plentiful waters in British Columbia and the Great Lakes. Analysts have argued, however, that effective water conservation measures would permit meeting of all essential needs now and in the immediate future from supplies within the United States (Frederick and Gleick, 1999). In the longer term, if drying continues as projected, this may not be the case.

Recognizing the potential for interest in exporting of Great Lakes water, the governors of the eight Great Lakes states, in co-operation with Ontario and Quebec, have negotiated an agreement (2005) pursuant to the earlier Great Lakes Charter Annex (2001). This agreement calls for no diversions out of the Great Lakes basin, with some exceptions. A 'grandfather' clause exempts the substantial (3200 cfs) diversion of Lake Michigan waters into the Mississippi River system at Chicago. The amount of this diversion is governed by a United States Supreme Court ruling. The other exception to the Great Lakes Annex Agreement prohibition on diversions outside the basin is for straddling counties and communities, those whose borders, as of 2005, straddle the watershed boundary of the Great Lakes.

With the expectation that increased evaporation due to climate change will lower Great Lakes levels and flows of the rivers in the system, including the St. Lawrence, adverse impacts on shipping, hydroelectric power generation and water quality are projected (Great Lakes Water Quality Board, 2003). This is without further diversions out of the system. Canada and the provinces need to remain vigilant to this threat, as well as the promotion of conservation by all jurisdictions. A recent amendment to the International Boundary Waters Treaty Act by Canada prohibits bulk-water removals and diversions from border and transborder waters but does not deal with attempts to divert internal Canadian waters, an issue that a number of provinces have similarly addressed.

Mexico also has very limited and declining supplies in regions bordering United States and has, at times, looked north to Canada for additional supplies. There remains a debate among trade experts as to whether water export would be expected or required under the terms of the North American Free Trade Agreement (NAFTA). There is no specific prohibition on export of water under this agreement, nor is there an obligation for bulk export of water. However, bulk export in one region may set a precedent.


Energy goods are an important part of Canada's export basket.6 Energy exports to the United States (which accounts for over 95% of Canada's energy exports) increased at an average annual rate of almost 17% during the decade from 1996 to 2005 (Table 5). Canada exports natural gas, crude oil, non-crude oil, electricity and coal to the United States.

Climate cha nge will alter the demand for energy in Canada and the United States, which will likely affect energy exports. Climate change will also affect Canada's supply of hydroelectricity and its electricity exports to the United States. Finally, efforts to reduce greenhouse gas emissions will likely change the export markets for different energy products.

Energy Demand

Climate change will lower space-heating demand in Canada, which will reduce natural gas and home heating oil consumption (Bhartendu and Cohen, 1987; Findlay and Spicer, 1988). It will also increase the air conditioning load, which will increase electricity demand during the summer months. The air conditioning demand rises faster than the annual average temperature. A 3 °C increase in mean daily maximum temperature increases the mean peak power demand by 7% (1200 MW; Colombo et al., 1999). In Canada, however, the overall energy demand is expected to decline over the coming few decades.

Table 5: Canada's energy exports to the United States (Industry Canada, 2006).
Value (millions of 2005 dollars) Average annual
growth 1
1996 1997 1999 2000 2002 2003 2005
Natural gas and natural gas liquids 9 875 10 906 12 106 22 924 10 391 28 484 38 807 20.2%
Crude oil 10 970 11 390 10 121 19 334 18 015 20 414 29 913 15.4%
Non-crude oil 3 464 3 402 3 327 5 615 7 036 8 006 10 972 15.9%
Electrical energy 1 218 1 377 1 923 4 059 1 812 1 852 3 168 19.5%
Coal and coal-based solid fuels 88 66 55 120 162 150 260 19.9%
Other energy goods 418 515 541 643 722 678 897 9.3%
Total energy exports to the United States 26 032 27 657 28 073 52 693 48 139 59 584 84 017 16.9%
Total exports to the United States 223 177 243 888 308 076 359 289 345 366 326 700 365 741 5.9%
Energy exports as percentage of total exports to U.S. 11.7% 11.3% 9.1% 14.7% 13.9% 18.2% 23.0%  

1 average of year-on-year growth over 10 years; overall average growth is higher

In the United States, the larger impact will be on the air conditioning load, thus causing overall energy demand to rise (Edwards, 1991; Sailor and Mu ñoz, 1997; Considine, 2000; Sailor, 2001; Amato et al., 2005). A 5°C temperature rise by 2100 would lead to a $40 billion welfare loss due to increased energy demand (Mansur et al., 2005). Changes in the energy demand in Canada will affect the energy available for export, and the increased energy demand in the United States will affect its energy imports.


Canada has abundant coal resources, mainly in the west (National Energy Board, 2003). About 90% of the coal produced in Canada is used to generate electricity in Alberta, Saskatchewan and northwestern Ontario. Coal for electricity generation in southern Ontario, New Brunswick and Nova Scotia is imported. Coal exports are primarily metallurgical coal for Asian markets. Record demand due to increased air conditioner use and reduced supply of hydroelectric energy due to drought-like conditions contributed to Ontario's decision to delay shutdown of the coal-fired generating units in the province (Independent Electricity System Operator, 2006). Closing the coal plants would reduce coal imports from the United States.

Crude Oil

Crude oil resources are located mainly in western Canada, but also in northern Canada and offshore Newfoundland and Nova Scotia (National Energy Board, 2003). Production of conventional crude oil is declining in western Canada and is expected to peak within the next decade on the east coast (National Energy Board, 2003). Oil sands production is projected to rise rapidly during the next two decades, more than offsetting the declining output from conventional sources (National Energy Board, 2003).

Canadian crude oil supplies refineries in western Canada and the United States. Refineries in eastern Canada use imported crude oil. As a result, more than half of Canada's production is exported to the United States. American imports are forecast to increase, but Canada's share is expected to remain at about one-third (Energy Information Administration, 2006). American efforts to increase energy security could reduce imports, possibly including those from Canada.

The main effect of climate change on Canada's oil exports is likely to be the impact of reduced water supplies in northern Alberta on oil sands production (Bruce, 2006; Schindler and Donahue, 2006). Since bitumen extraction and upgrading uses substantial amounts of water, presently projected rates of oil sands development may have to be reduced if instream flow requirements for the Athabasca River are to be met downstream (Bruce, 2006). Improved efficiency in water use would be a valuable adaptation.

Natural Gas

Natural gas is produced in western Canada and offshore Nova Scotia, and there are extensive reserves in the Arctic (National Energy Board, 2003). Production is forecast to remain roughly constant, unless or until a pipeline to bring gas from the Arctic is completed (National Energy Board, 2003). About half of Canada's output is currently exported to the United States, but exports are expected to decline as production declines and domestic demand rises (National Energy Board, 2003). Although the space-heating demand in Canada is expected to decline due to climate change, other uses are expected to grow, leading to an increase in domestic demand for natural gas (National Energy Board, 2003).


About 60% of Canada's electricity generation is hydro based and most of the balance is coal produced, but the mix varies significantly by province. Historically, 7 to 9% of Canada's electricity has been exported to the United States, mainly from hydro-rich regions: British Columbia, Manitoba and Quebec. Electricity imports average about a quarter of the exports. Imports are driven by cross-border differences in peak periods and opportunities for utilities with hydro storage capacity to buy off-peak power and sell more during peak periods.

In the United States, about half of the electricity is generated from coal, and electricity generation is responsible for almost 40% of CO2 emissions (Energy Information Administration, 2006). Given the long lives of generating facilities, changes to the generation mix are likely to occur gradually (Morgan et al., 2005). Climate change is projected to reduce the hydroelectric generation potential of the Colorado and other western rivers, especially during the summer months when the electricity is most needed to meet the rising air conditioning load (Edwards, 1991; Christensen et al., 2004).

The availability of hydroelectricity in Canada to meet the rising air conditioning demand in the United States (and Canada) may be compromised by climate change as well. Although climate change is projected to increase hydroelectric generation potential in northern Quebec and Labrador (Mysak, 1994; Mercier, 1998), the experience over the period since 1970 is for reduced flows on most major rivers flowing to Hudson, James and Ungava bays, except the Nelson River (D éry et al., 2005). In Ontario and on the Prairies, hydroelectric generation potential would likely be reduced, except from the Winnipeg and Nelson rivers. In southeastern British Columbia, a projected small increase in precipitation, combined with increased reservoir evaporation due to higher temperatures, could reduce hydroelectric generation potential, especially if instream flow needs and irrigation needs downstream are to be met (Raban, 1991; Mercier, 1998; Payne et al., 2004). Declines in levels of the Great Lakes, and thus flows of the Niagara and St. Lawrence rivers, have been projected to reduce hydroelectric power generation by up to 17% by 2050 (Tin, 2006).

Meeting the increased air conditioning load in North America, while coping with reduced hydroelectric production in some regions and reducing greenhouse gas emissions, will pose a challenge for electric utilities. The simplest solution to this challenge would be to meet the higher demand with more gas-fired generation, which is well suited to serving peak loads. But the scope for this option is limited, due to the anticipated supply constraints and price increases for natural gas. Renewable energy sources, such as wind and solar, generate electricity when conditions are favourable and cannot be relied upon to meet the air conditioning demand when it occurs. Nuclear generating stations are best suited to providing a constant supply of electricity and are therefore less well suited to serving a variable load, such as air conditioning demand. Utilities in both countries will probably need to rely on a mix of demand-side measures, such as energy efficiency, and generation actions to cope with the changes in demand.


Canada is the world's largest producer and exporter of uranium, the fuel for nuclear generators. Global efforts to reduce greenhouse gas emissions could lead to more nuclear power generation in some countries. That could lead to higher exports of uranium for Canada.


Climate change will reduce energy use for space heating, thus saving natural gas and home heating oil. The natural gas saved will simply moderate the expected North American shortage.

Utilities in Canada and the United States will need to rely on a mix of energy efficiency and generation options specific to their region to cope with the demand. The challenge will be greater in the United States due to its greater reliance on coal-fired generation and larger projected growth in air conditioning load. It does not appear that Canada will be able to substantially increase exports of electricity or natural gas to help meet the United States demand.


Although the transborder transport of atmospheric pollutants between the United States and Canada has been well documented for acid rain and some contaminants, there has been little attempt to assess the potential impacts of climate change on these movements. Such impacts, positive or negative, can arise from:

  • changes in average circulation patterns, especially in hot spells;
  • increases in average air temperature and hot spells, and effects of sunlight on atmospheric chemical processes; and
  • remedial actions to address air quality and emission reduction.

The regions of Canada currently most affected are southern Ontario and Quebec, southwestern New Brunswick and Nova Scotia, southern British Columbia and southwestern Alberta.

The main concerns are ground-level ozone concentrations, small particulate matter (PM 2.5), acid deposition, mercury and several other toxic chemicals. The human health and ecosystem effects of these atmospheric contaminants are addressed in the regional chapters, especially Ontario and Quebec. An estimate of premature deaths from these causes for a total of eight cities across Canada is 5900 per year (Judek et al., 2004).

For the critical Canada-United States transborder air-pollution issues, the two countries agreed on pollution control measures to lessen the impacts through the Canada -United States Air Quality Agreement of 1991 and its Ozone Annex of 2000 (Canada-United States Air Quality Committee, 2006). Areas of special concern are the Georgia Strait region of the Pacific Coast and the Great Lakes -St. Lawrence River area. The 2006 Progress Report notes that 3-year average ground-level ozone levels remained unacceptably high in 2002 to 2004. The highest daily maximum 8-hour average ozone concentration exceeded 95 ppm in southwestern Ontario and 80 ppm in a much larger area southwest of a line between the Ottawa Valley and the north end of Georgian Bay. This situation occurred in spite of successful programs in both countries that reduced the chemical precursors, volatile organic compounds (VOCs) and nitrous oxides (NOx). High ozone concentrations occur in smog episodes during hot spells, which are more frequent in the changing climate, when high temperatures and sunlight act upon the emitted precursor chemicals to create ozone.

The average annual number of smog advisories increased from 7 during 1993 to 1998 to 24 during 2000 to 2005, with a record of 53 in 2005 (Yap et al., 2005). The duration of 'warm spells' in the Great Lakes region increased between 1951 and 2003 (Alexander et al., 2006). Heat episodes (defined as temperature >30°C) are projected to double by 2050 and more than triple by 2080 (Cheng et al., 2005). More intense, more frequent and longer lasting heat waves are projected for both Europe and North America (Meehl and Tebaldi, 2004). Thus, the changing climate may prevent the air-pollution control efforts from having the desired effect of reducing ozone concentrations. Such warm-spell smog episodes are also periods of high particulate (PM 2.5) concentrations. It is estimated that transborder pollutants account for 99% of smog events in Windsor and 84% of events downwind of Toronto (Yap et al., 2005). In Quebec, pollutant sources in such events are estimated to be 30% from the United States and 30% from Ontario, with the balance locally generated. To reduce future health risks, it will be necessary to redouble efforts to reduce NOx and VOCs in Canada and the United States.

Acid deposition to Canada's lakes and forests has been somewhat ameliorated by reductions in SO2 emissions in the United States and Canada (Canada-United States Air Quality Committee, 2006). Nevertheless, the effects of these improvements in aquatic ecosystems are influenced by lake characteristics and climate interactions (Canada -United States Air Quality Committee, 2006), and many lakes do not yet show signs of recovery. Work at the Experimental Lakes area in northwestern Ontario suggests that climate change is a factor in slowing the positive response of lakes (Schindler et al., 1996).

Further research and monitoring are required to address knowledge gaps with respect to the interaction in lake ecosystems between acid deposition and climate change, and the impacts of climate trends on transport of toxic chemicals.

5 Glacier National Park had 150 glaciers in 1850; in 2005, it had 27; by 2050, it is expected to have none.
6 Energy goods are defined here as those goods covered under NAFTA's chapter 6: 'Energy and Basic Petrochemicals'. They include most refined and unrefined hydrocarbon products, uranium and electricity.