"Global climate change would disturb the Earth's physical systems and ecosystems; these disturbances, in turn, would pose direct and indirect risks to human health." ⁽²⁰⁾

Our health and well-being are strongly influenced by weather and extreme events. A changing climate would affect mortality and injury rates, illnesses and mental health. These impacts would result from changes in factors such as temperature extremes, air quality, water- and vector-borne diseases, and extreme weather events. The impacts would vary across the country, with different regions facing different priority issues. Some of the key health-related concerns in the Prairie Provinces are shown in Box 1.

BOX 1: Climate-related health issues in the Prairie Provinces^{(21, 22, 23)}

Researchers in the Prairies used round-table discussions, e-mail communications and a literature review to docume nt possible human health effects of climate change, and to identify priority research areas. This work revealed that key concerns for the Prairie Provinces include: impact of drought on stress levels in farming communities; effects of forest fires on air quality; increased probability of food-borne illness; impacts of heat waves on vulnerable populations; contamination of surface water due to extreme rainfall events; and effects of floods and other hazards on physical safety and mental health. Photo courtesy of Prairie Farm Rehabilitation Administration.

Temperature Stress

Climate change is projected to cause milder winters and warmer summers. People will largely be able to adapt to gradual changes in average temperatures through normal acclimatization. However, higher air temperatures are also expected to increase the frequency and intensity of heat waves.⁽¹⁶⁾ Heat waves can exceed the physiologic adaptive capacity of vulnerable groups, such as infants, the elderly and those with pre-existing health conditions. The impacts of heat waves tend to be greater in urban, rather than suburban or rural areas, likely owing to both the 'heat island' effect (see Figure 2) and higher levels of air pollution.⁽¹⁶⁾ Studies have suggested that an increase in the number of days of extreme heat (above 30°C) over this century, would result in greater heat-related mortality in some urban centres in southern Canada.^{(24, 25)} However, it should be noted that seasonal acclimatization and appropriate adaptation measures, such as access to air conditioning and necessary medical care, could reduce the number of deaths.⁽²⁶⁾

Research suggests that the timing and characteristics of heat waves may influence the degree of health impacts. For example, heat waves that occur earlier in the summer tend to result in more deaths than those that occur later in the season, as people have not yet acclimatized to warmer weather.⁽²⁷⁾ In addition, current warming trends show that night-time minimum temperatures are increasing more rapidly than daytime maximum temperatures, and climate models suggest that this trend will continue.⁽²⁸⁾ This means that, during future heat waves, there would be less relief due to night-time cooling than there is at present, and this would further increase temperature stress.⁽²⁹⁾

Figure 2: Urban heat island profile. larger image [JPEG, 42.5 kb, 800 X 488, notice]

As well as affecting mortality rates, extreme high temperatures would also influence a range of heat-related illnesses. Direct impacts of extreme heat include heat fatigue, exhaustion, heat rash, cramps and edema, as well as heat stroke and sunstroke. Indirect impacts, such as pre-existing health conditions exacerbated by extreme heat, cover a wide range of circulatory, respiratory and nervous system problems.⁽³⁰⁾ Factors that increase the risk of heat-related illnesses include old age, medication use (especially anticholinergic and psychotropic medications), obesity, previous heat injury and skin disorders.⁽³¹⁾ Heat-related illnesses place additional stress on health infrastructure and can cause significant economic costs.⁽³⁰⁾ Studies suggest that, although heat-related health effects are reflected in hospital admissions (see Box 2), the relationship can be difficult to quantify because ambulance and hospital admission records are presently not designed to capture such data.

In the far north, summers tend to be shorter and cooler, and people and animals are acclimatized to lower temperatures than those characteristic of southern Canada.⁽³²⁾ Therefore, what constitutes a health-threatening heat wave in the northern territories may be quite different than in southern Canada.

Although cold snaps will continue to be a problem in the future,^{(33, 34)} researchers project that the frequency of extreme cold events will decrease, with resultant benefits for the health care sector. Throughout Canada, during the second half of the 20th century, there were many more deaths due to excessive cold than from excessive heat (2 875 versus 183, respectively, between 1965 and 1992).⁽¹⁷⁾ A reduction in extreme cold events would be especially beneficial for the homeless, who may be unable to obtain the shelter necessary to avert cold-related illness and death.

BOX 2: Identifying heat-related illnesses and death⁽³⁰⁾

Air Pollution and Related Diseases

Air quality influences many respiratory ailments. Although the average concentrations of toxic air pollutants in Canada have generally been reduced to fairly low levels, relative to those experienced 50 years ago, the daily and seasonal rises in levels of air pollution are still closely followed by peaks in the number of people admitted to hospitals or dying of respiratory and circulatory diseases.^{(35, 36)} Air pollution causes and exacerbates acute and chronic illnesses, such as lung disease, and results in increases in health care costs and premature deaths.⁽³⁷⁾ Air quality is especially a concern in the most populous regions of Canada, including the Windsor to Québec corridor and the lower Fraser Valley of British Columbia, where summer air pollution levels often reach hazardous levels. Indeed, it is estimated that approximately two-thirds of Canadians live in regions that suffer from high smog levels in the summer.⁽³⁸⁾ Children and the elderly are groups considered particularly susceptible to poor air quality.⁽³⁹⁾

Climate change could affect both average and peak air pollution levels.⁽²⁴⁾ For example, background concentrations of ground-level ozone (a pollutant that irritates the lungs and makes breathing difficult) are expected to increase over mid-latitudes due, in part, to higher temperatures,⁽¹⁶⁾ whereas intense smog episodes are projected to become more frequent during summer months as a result of climate change.⁽²⁴⁾ Higher summer temperatures are also likely to increase energy consumption for cooling, thereby adding to pollution emissions.⁽³⁸⁾ There is general recognition, however, that shifts to cleaner energy sources⁽⁴⁰⁾ and other reductions in greenhouse gas emissions^{(41, 42)} will yield health benefits.

Airborne particulates from natural sources, such as forest fires and wind erosion, also have the potential to increase as a result of climate change. During recent drought years, large forest fires have spread smoke across areas covering more than 200 000 square kilometres.⁽⁴³⁾ In July 2002, smoke from large forest fires in Quebec caused New York to issue a statewide alert for people with respiratory and heart conditions to remain indoors.⁽⁴⁴⁾ Particulates in forest fire smoke can irritate the respiratory tract when they are inhaled.⁽⁴⁵⁾ Forest fires could increase in frequency and severity in some regions of Canada as a result of future climate change (see Forestry chapter).

An increase in drought could also lead to increased concentrations of dust in the air due to wind erosion of soils,⁽³⁸⁾particularly on the Prairies, where dust storms presently represent a significant natural hazard.⁽⁴⁶⁾ Alkali dust emissions, resulting from wind erosion of dried salt lake beds, have caused nasal, throat, respiratory and eye problems for some rural residents on the southern Prairies and could become more common if climate change results in further drying of saline lakes in this region.⁽⁴⁶⁾

Waterborne Diseases

Heavier rainfall events and higher temperatures resulting from climate change may increase the occurrence of waterborne diseases, such as giardiasis and cryptosporidiosis. Although such diseases are generally not serious for most of the population, the very young, the elderly and those with compromised immune systems may be vulnerable. Heavy rainfall events and flooding can flush bacteria, sewage, fertilizers and other organic wastes into waterways and aquifers (see Water Resources chapter). If not properly treated, such events can lead to the direct contamination of drinking water supplies.

Recent examples of waterborne disease outbreaks related, at least in part, to climatic conditions include those caused by E. coli in Walkerton, Ontario (2000); Cryptosporidium in Collingwood, Ontario (1996); and Toxoplasma in the greater Victoria area, British Columbia (1995). In Walkerton, expert witnesses testified that the outbreak, which resulted in seven deaths and thousands of illnesses, could be partly attributed to an unusually heavy rainfall event, which followed a period of drought.⁽²⁵⁾ Such trends are receiving growing recognition; researchers have determined that more than 50% of waterborne disease outbreaks in the United States between 1948 and 1994 were preceded by extreme precipitation events.⁽⁴⁷⁾ A detailed discussion of the causes and history of infectious diseases associated with contaminated drinking water in Canada is provided by Krewski et al.⁽⁴⁸⁾

Increases in temperature would also exacerbate water contamination, as higher temperatures encourage the growth and subsequent decay of algae, bacteria and other micro-organisms, causing odour and taste problems and, in extreme cases, even rendering the water toxic (reference 49; see also Water Resources chapter). In addition, higher water temperatures and storm water runoff, combined with greater use of beaches, have been associated with increases in infectious illnesses in people using recreational waters.⁽⁵⁰⁾

Food-Borne Diseases

An increase in heavy rainfall events and higher temperatures may increase the occurrence of toxic algal outbreaks in marine environments (reference 51; see also Fisheries chapter). Toxic algal blooms can contaminate shellfish, which in turn pose a danger to human health through paralytic shellfish poisoning. Increased problems with contamination of both domestic and imported shellfish are possible. Food poisoning from contamination of other imported foods may also increase, as rising air temperatures allow microbes to multiply more quickly.⁽⁵²⁾

Vector- and Rodent-Borne Diseases

Vector-borne diseases are infections that are transmitted to humans and animals through blood-feeding arthropods, such as mosquitoes, ticks and fleas. Insect- and tick-borne diseases, such as West Nile virus, Eastern and Western Equine Encephalitis (transmitted by mosquitoes), Lyme disease and Rocky Mountain Spotted Fever (transmitted by ticks),^{(53, 54)} already cause human health problems in some parts of Canada. Rodent-borne viruses, capable of causing illnesses and deaths in humans, are also present in much of southern Canada.⁽⁵⁵⁾ Hantaviruses, which can cause fatal infections (pulmonary syndrome), are of particular public health concern because the deer mice that carry hantaviruses tend to invade dwellings and are present across Canada as far north as the Yukon Territory and the Northwest Territories.^{(56, 57)} Rodents may also carry tick-borne diseases, such as Babesiosis.⁽⁵⁸⁾

There are concerns that future changes in climate could lead to conditions that are more favourable for the establishment and/or proliferation of vector- and rodent-borne diseases.⁽²⁴⁾ The impacts of climate change on these diseases are generally expected to result from the effects of changing temperature, rainfall and humidity on the vector species, although the development rates of the pathogens themselves may also be affected. For example, longer and warmer springs and summers resulting from climate change could increase mosquito reproduction and development, and also increase the tendency of mosquitoes to bite.⁽²⁹⁾ Mosquitoes would also benefit from warmer winters, as cold temperatures currently reduce mosquito populations by killing mosquito eggs, larvae and adults.⁽²⁹⁾ Furthermore, increases in extreme weather events, especially those that trigger flooding, could increase breeding areas for mosquitoes by creating more shallow pools of stagnant water.⁽²⁹⁾

Observed trends in Lyme disease and West Nile virus illustrate how quickly new and emerging diseases can spread. For example, Lyme disease has extended its range significantly across the United States since the 1980s, and is now considered to be a major public health concern.⁽⁵⁹⁾ Although the disease is still rare in Canada, warmer weather and the northward migration of animals and birds that carry infective ticks could further expand its range.⁽³⁸⁾ The recent, extremely rapid spread of West Nile virus across the United States and Canada, although not due to climate change, is another example of how quickly and widely a newly introduced virus can expand its range. Conditions expected to result from climate change could further facilitate the spread of the virus northward.⁽³⁸⁾

Another potential future health concern in Canada is the re-emergence of malaria as a result of climate change, increased travel and immigration, and increased drug resistance.⁽⁶⁰⁾ Malaria-infected persons exposed to North American mosquitoes capable of transmitting the causative Plasmodium parasite can cause localized outbreaks of infections.^{(60, 61, 62)} In addition, new insect vectors, such as the 'tiger mosquito', which has spread across 25 states since its introduction to the US from Asia in 1987,⁽⁶³⁾ may extend their range to southern Canada if climate conditions become more favourable.⁽³⁸⁾ Nevertheless, there remains considerable uncertainty regarding how climate change will affect vector lifecycle and disease incidence of malaria, especially in a North American context.

Allergens

Changes in temperature, precipitation and length of the growing season would all impact plant growth and pollen production, and ultimately human health by, for example, extending the allergy season.⁽¹⁶⁾ Studies have also shown that elevated concentrations of atmospheric carbon dioxide can enhance the growth and pollen production of ragweed, a key allergy-inducing species.⁽⁶⁴⁾ Although not all species of allergen-producing plants will necessarily react in a positive manner to changed climate conditions, a more stormy climate may sweep more allergens into the air and lead to more frequent allergy outbreaks.⁽⁶⁵⁾ Stormy winds may also increase airborne concentrations of fungal spores, which have been shown to trigger asthma attacks.⁽⁶⁶⁾

Ultraviolet (UV) Radiation

Exposure to ultraviolet (UV) radiation is expected to rise in future, leading to an increase in temporary skin damage (sunburn), eye damage (e.g., cataracts) and rates of skin cancer.^{(67, 68)} Increased UV exposure could result from a number of factors associated with climate change, including stratospheric ozone depletion due to increased concentrations of some greenhouse gases, and increased development of high-altitude clouds.⁽³⁸⁾ Longer summer recreational seasons resulting from global warming may also contribute to increased population exposure to solar UV radiation.

Effects on Human Behaviour

Climate also has an influence on mental health. This is particularly evident in the case of climate-related natural hazards, where property losses and displacement from residences can cause significant psychological stress, with long-lasting effects on anxiety levels and depression.⁽²³⁾ Social disruptions resulting from family and community dislocations due to extreme weather events pose a special stress for children⁽⁶⁹⁾ and those of lower socio-economic status.⁽⁷⁰⁾ Increased levels of anxiety and depression were seen among farmers experiencing crop failures due to drought⁽²³⁾ and among victims of the 1997 Red River flood.⁽⁸⁾

Temperature also appears to influence human behaviour. In the Montréal area, researchers found that the number crimes per day tended to increase with daily maximum temperature up to about 30°C.⁽⁷¹⁾ Another study found that higher summer temperatures are linked to increases in human aggression.⁽⁷²⁾ Linkages may also exist between extreme climate events, aggression and crime rates. For instance, increased aggression could result from crowding of disoriented and distressed people in temporary emergency shelters.⁽⁷³⁾ A recent study examined how the ice storm of 1998 affected crime rates in three regions of Quebec (see Box 3).

BOX 3: Crime rates during the 1998 ice storm⁽⁷³⁾

Health Impacts in Northern Canada

In addition to being affected by many of the health concerns listed in Table 1, communities in northern Canada will face additional challenges resulting from the impacts of climate change on the physical and biological environments in the North. There is strong evidence that northern regions are already experiencing the impacts of climate change, particularly changes in the distribution and characteristics of permafrost, sea ice and snow cover.^{(74, 75, 76)} For example, residents of Nunavik and Labrador reported changes in the physical environment, over the last 20 to 30 years, that have had discernible effects on travel safety and on their ability to hunt traditional food species and obtain access to clean drinking water.⁽⁷⁵⁾ There is concern among northern communities that such impacts will continue and worsen in the future (see Box 4).

BOX 4: Health impacts in Nunavik and Labrador⁽⁷⁵⁾

In this study, researchers examined the potential health impacts of climate change on communities in Nunavik and Labrador by integrating information from scientific and Inuit knowledge. In addition to conducting literature reviews and consultations with scientists and health professionals, the researchers also worked with groups of elders, hunters and women in the region. This allowed them to develop a better understanding of the main concerns related to climate change for communities in this area. The researchers used the information gathered to produce a series of fact sheets and identify areas in need of further research. This work will help northern decision-makers and residents deal with the potential impacts of climate change. Kuujjuaq, Nunavik. Photo courtesy of S. Bernier.

Another concern for northern residents is the possible impact of climate change on traditional food sources (see Coastal Zone chapter). Higher temperatures may accelerate both the loading of the northern environment with pollutants and the release of pollutants from soils and sediments into ecosystem food webs. For example, research suggests that climate warming could enhance the uptake of toxic metals by fish. Elevated levels of cadmium and lead in Arctic char have been attributed to higher fish metabolic rates, induced by higher water temperatures and longer ice-free seasons (see Fisheries chapter; reference 77). The safety and benefits of traditional food sources are an important issue for northern residents.

In addition, a warmer climate could make it more difficult to safely conserve perishable foods through cold storage in snow or ice, or through natural freezing.⁽⁷⁶⁾ Poisoning (botulism) from traditional foods stored at insufficiently low temperatures has been a recurring public health problem in Alaska, and is being addressed by educational programs.⁽⁷⁸⁾