Global climate change would disturb the Earth's physical systems (e.g., weather patterns) and ecosystems (e.g., disease vector habitats); these disturbances, in turn, would pose direct and indirect risks to human health. Direct risks involve climatic factors that impinge directly on human biology. Indirect risks do not entail direct causal connections between climatic factors and human biology (McMichael, 1996; McMichael et al., 1996). Health care will significantly help people to adapt to climate change. Unfortunately, not everyone has adequate health care; for example, in 1996, nearly 18% of Americans did not have access to a doctor's office, clinic, health center, or other source of health advice or treatment (Miller et al., 2000).

15.2.4.1. Potential Direct Health Impacts of Climate Change

15.2.4.1.1. Health impacts of thermal extremes

In a warmer world, heat waves are expected to become more frequent and severe, with cold waves becoming less frequent (Kattenberg et al., 1996). Increased frequency and severity of heat waves may lead to an increase in illness and death, particularly among the young (CDC, 1993), the elderly (Ramlow and Kuller, 1990; CDC, 1993; Semenza, 1999; Patz et al., 2000), the poor (Schuman, 1972; Applegate et al., 1981), the frail and the ill, and those who live in the top floors of apartment buildings and lack access to air conditioning (Patz et al., 2000), especially in large urban areas (CDC, 1989; Grant, 1991; Canadian Public Health Association, 1992; Kalkstein, 1993, 1995; Kalkstein and Smoyer, 1993a,b; Canadian Global Change Program, 1995; Environment Canada, 1995; Guidotti, 1996; Kalkstein et al., 1996a,b; Tavares, 1996; Last et al., 1998). Other vulnerable people are those who take medications that affect the body's thermoregulatory ability (Marzuk et al., 1998; Patz et al., 2000).

Heat waves affect existing medical problems, not just those related to problems of the respiratory or cardiovascular systems (Canadian Global Change Program, 1995). Morbidity—such as heat exhaustion, heat cramps, heat syncope or fainting, and heat rash—also results from heat waves (Shriner and Street, 1998; Patz et al., 2000).

In the United States, populations in northeastern and midwestern cities may experience the greatest number of heat-related illnesses and deaths in response to increased summer temperatures (Patz et al., 2000). Recent episodes include the heat-related deaths of 118 persons in Philadelphia in 1993 (CDC, 1993), 91 persons in Milwaukee in 1995, and 726 persons in Chicago in 1995 (CDC, 1995; Phelps, 1996; Semenza et al., 1996, 1999). This follows several episodes in the 1980s, particularly in 1980, 1983, and 1988 (CDC, 1995).

In Canada, urbanized areas in southeastern Ontario and southern Quebec could be "impacted very negatively" by warmer temperatures. An "average" summer in 2050 could result in 240-1,140 additional heat-related deaths yr^-1 in Montreal, 230-1,220 in Toronto, and 80-500 in Ottawa, assuming no acclimatization (Kalkstein and Smoyer, 1993b). The significance of these estimates is demonstrated by the fact that a total of only 183 Canadians died as a result of excessive heat for the years 1965-1992 (Duncan et al., 1998). Heat-related illness and death are largely preventable through behavioral adaptations, such as use of air conditioners and increased intake of fluids. In the United States, use of air conditioning is expected to become nearly universal by the year 2050 (U.S. Census Bureau, 1997a,b). Other adaptive measures include development of community-wide heat emergency plans, improved heat warning systems, and better heat-related illness management plans (Patz et al., 2000).

Finally, it is important to note that in a warmer world, cold waves are expected to become less frequent. For example, in Saskatoon, Canada, the number of January days with temperature below -35°C could decrease from the current average of 3 days yr^-1 to 1 day every 4 years (Hengeveld, 1995). Currently, more people die of cold exposure than heat waves. Therefore, an expected decrease in cold waves is likely to have a beneficial effect—a decrease in weather-related mortality.

15.2.4.1.2. Health impacts of extreme weather events

It has been postulated that there will be increases in the frequency and severity of extreme events, which may result in an increase in deaths, injuries, toxic contamination or ingestion, infectious diseases, and stress-related disorders, as well as other adverse health effects associated with social disruption, environmentally forced migration, and settlement in poorer urban areas (McMichael et al., 1996). Adaptive measures to counter the health impacts of extreme events include improved building codes, disaster policies, warning systems, evacuation plans, and disaster relief (Noji, 1997).

15.2.4.1.2.1. Convective storms

There is some evidence of increases in the intensity or frequency of some extreme events at regional scales throughout the 20th century. Frequencies of heavy precipitation events have been increasing in the United States and southern Canada (Easterling et al., 2000). Unfortunately, it is difficult to predict where these storms will occur and to identify vulnerable populations. In 1997, severe storms caused 600 deaths and 3,799 reported injuries in the United States.

Patients with specific allergies to grass pollen are at risk of thunderstorm-related asthma (Venables et al., 1994; Celenza et al., 1996; Hajat et al., 1997; Knox et al., 1997; Suphioglu, 1998). Thunderstorm-associated asthma epidemics in Melbourne, Australia (1987/1989), and London, England (1994), placed considerable demands on the health system. Several London health departments ran out of drugs, equipment, and doctors (Davidson et al., 1996). It is unclear if this situation could arise in North America.

IPCC Homepage