The Regional Impacts of Climate Change

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9.3.8. Human Health

Climate change-related disturbances of physical systems (e.g., weather patterns, sea level, water supplies) and ecosystems (e.g., agro-ecosystems, disease-vector habitats) could pose risks to the health of human populations. Some health impacts would occur via direct pathways (e.g., death from heat waves and other extreme weather events, such as hurricanes); others would occur via indirect pathways (e.g., changes in the geographical range of vector-borne diseases). Researchers generally agree that most of the impacts of climate change on human health are likely to be adverse. The vulnerability of populations to such threats will depend on many factors, including present health status, quality of available health care services and associated infrastructure, and availability of financial and technical resources (McMichael, 1993).

Should global warming increase the frequency and/or severity of extreme weather events such as droughts, floods, landslides, and tropical cyclones, it is likely that more deaths, injuries, infectious disease cases, and psychological disorders could result (McMichael and Martens, 1995; IPCC 1996, WG II, Section 18.2.2). Elevated global mean temperatures also could lead to a greater frequency of heat waves-and consequently a higher incidence of related illness (predominantly cardiorespiratory) and mortality. Inevitably, the most vulnerable countries will be those with reduced capacity to respond to or mitigate these threats. Because of their present social and economic circumstances, many small islands fall into this category.

The transmission of many infectious diseases is affected by climatic factors. Vector-borne diseases such as malaria, dengue, and yellow fever are sensitive to factors such as temperature, rainfall, and humidity. Climate change could increase the geographical range of disease agents; changes in the life-cycle dynamic of vectors and infective agents, in aggregate, could result in more efficient transmission of many vector-borne diseases (McMichael et al., 1996). Mathematical models project that an additional 50-80 million cases of malaria would result from a mean temperature increase of 3.0�C (Martens et al., 1995). Although most of this projected increase is expected to be in temperate-zone countries, some increase in the tropics-the latitudinal zone in which the majority of small islands and other developing countries are located-cannot be ruled out (see Table 9-3). Moreover, even a marginal increase in the incidence of disease would place great stress on the public health systems of many small islands, where these facilities often are not well developed.

Table 9-3: Estimated impacts of climate change on tropical vector-borne diseases.

Population at Risk (millions)
Prevalence or Incidence of Infection
Present Distribution
Possible Change of Distribution due to Climate Change (1)

300-500 million
200 million
Lymphatic filiariasis
117 million
African trypanosomiasis
250,000-300,000 new cases/yr
Tropical Africa
Tropics (Africa/Asia)
Visceral leishmaniasis
12 million (prevalence) + 500,000 new cases/yr
Asia/S. Europe/ Africa/South America
17.5 million
Africa/Latin America
American trypanosomiasis
18 million
Central and South America
50 million/yr
Yellow fever
<5,000 cases/yr
Africa/Latin America/ East and Southeast Asia

1 += likely; ++ = very likely; +++ = highly likely; ? = unknown.

Source: WHO, 1996.

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