Increasing temperatures alter the risk of direct and indirect weather-related impacts on human health, from cardiovascular and respiratory illnesses to infectious diseases (Patz et al., 2005). Quantifying the impact per degree of global temperature change, however, is complicated by confounding factors such as human behavior and socioeconomic conditions that affect exposure, transmission, and other aspects of risk (Patz et al., 2005). Here, we discuss three main aspects of health-related risks likely to be affected by climate change: heat-related illness and death, vector-borne disease, and health concerns related to poor air and water quality.

Heat-Related Illness and Death

Temperature extremes such as heat waves and periods of extreme cold are known to produce elevated rates of illness and death (McGeehin and Mirabelli, 2001). Together, these accounted for 75% of all deaths due to natural disasters from 1979-2004 (Thacker et al., 2008). From the 1970s through the 1990s, heat-related mortality in the United States declined due to acclimatization and increased use of air conditioning, then flattened out during the past decade (Sheridan et al., 2009).

In the future, extreme heat days and heat wave frequency, intensity, and duration is projected to increase with global mean temperature, while the frequency and intensity of winter cold is projected to decrease (Tebaldi et al., 2006; IPCC, 2007a). Under a 2ºC increase in global mean temperature by end-of-century, for example, the average number of days per year with maximum temperatures exceeding 38ºC or 100ºF across much of the south and central United States is projected to increase by a factor of 3. Under a 3.5ºC increase, the number of days is projected to increase by 5 to nearly 10 times historical levels (Figure 5.15).

Although the response of illness and death rates to changing heat extremes can be modified by acclimatization and adaptation strategies (Ebi et al., 2004), it is clear that risks of heat-related mortality increase with temperature, while cold-related mortality risks decrease (Gamble et al., 2008). Prolonged periods of extreme heat with little relief at night can have devastating effects on urban populations (Basu and Samet, 2002), increasing the risk of both illness and death due to heat stress (Martens, 1998; McGeehin and Mirabelli, 2001; Schär et al., 2004).

Temperature-related mortality is strongly linked to a wide variety of social, economic, and behavioral factors, even in industrialized nations such

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