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Global climate change over the coming decades could have various effects on the health of human populations within the European region. Because of the nature and scale of the exposures involved, such effects generally would apply to entire populations or communities rather than to small groups or individuals. Climate change could affect human health through six major pathways.
1) An increased frequency or severity of heat waves would cause an increase in heat-related mortality and illness. In contrast, less-severe cold weather would reduce the documented seasonal excess of deaths in winter. Many studies have shown that instances of heat hyperpyrexia and overall death rates rise during heat waves, particularly when the temperature rises above the local population's physiological threshold and the temperature increases are accompanied by high humidity. Several U.S. studies indicate that, on average, approximately one-third of these deaths would occur 2-3 weeks after the heat wave in susceptible persons, whereas other deaths apparently are unexpected. By applying these documented heat wave-associated risks to transient climate change scenarios associated with CO2-doubling, U.S. researchers have estimated that the number of heat-related deaths may increase several-fold in very large U.S. cities by 2050 (Kalkstein, 1993). In such cities, this would represent up to several thousand additional deaths per year.
No European-equivalent estimates of additional heat-related deaths attributable to climate change, based on local empirical studies, are yet available. A clear rise in daily mortality was associated with the 1995 extreme heat wave in the United Kingdom; the increase was approximately twice as great within the urban London population (Rooney et al., 1997). By simple extrapolation from a U.S. study, Fankhauser (1995) concluded that about 9,600 additional heat-related deaths per year may occur in the European Union for a 2.5�C temperature rise, and about 8,400 additional deaths may occur in the former Soviet Union. In both cases, full physiological acclimatization is assumed; population size, air conditioning, and medical care are assumed to be unchanged from present conditions.
This heat-related increase in deaths would be partially offset by reductions in cold-related deaths (predominantly cardiovascular). A recent study (Martens, 1997) estimated that in areas with temperate and cold climates-which includes large parts of the European continent-a globally averaged temperature increase of approximately 1�C could result in a reduction in winter cardiovascular mortality, especially in older people. Another British study (Langford and Bentham, 1995) has forecast that approximately 9,000 fewer winter-related deaths would occur annually by the year 2050 in England and Wales under a 2-2.5�C increase in average winter temperature. On the other hand, Fankhauser (1995) arrives (again by extrapolation from the United States) at about 800 fewer winter deaths for the entire EU. The EUROWINTER group (1997) assessed increases in mortality per 1�C decrease in temperature in various European regions. This study shows that mortality increased to a greater extent with a given decline in temperature in regions with warm winters, in populations with cooler homes, and among people who wore fewer clothers and were less active outdoors. Apparently there still is insufficient European information to quantify this trade-off between heat-associated losses and gains associated with milder winters. Furthermore, the balance will vary by location and adaptive response.
2) Changes in seasonal and daily temperatures and humidity are likely to affect the concentration of airborne materials that impinge on respiratory health. The production of photochemical smog proceeds more rapidly at higher temperatures. The concentrations and onset and duration of season of allergenic pollens and spores are related to cumulative temperatures and rainfall, though in a complex manner (Emberlin, 1994; Spieksma et al., 1995). Alterations in the concentration of aeroallergens may affect the seasonality of certain allergic respiratory disorders. Relatively little research has been done on these processes and relationships within Europe or elsewhere, however. Interactive adverse effects on mortality have been reported from Athens in response to simultaneous high temperatures and high levels of air pollution (Katsouyanni et al., 1993).
3) Extreme weather events (floods, storms, fogs, etc.) cause deaths, injury, certain infectious diseases, and mental health disorders. The number of victims of such events is relatively low in Europe (Alexander, 1993; IDNDR, 1994); for instance, the extremely stormy first quarter of 1990 caused "only" 225 casualties throughout Europe (Munich Re, 1993). Indications exist that flood incidence in the northern parts of Europe and storminess in the western and central parts of Europe (and hence health risks) may increase (Downing et al., 1996); to date, no research has been reported that quantifies the impact on mortality and morbidity risks. Disease (e.g., hepatitis) may break out in areas affected by severe flooding, particularly if drinking water becomes contaminated by sewage.
4) Organisms and biological systems that determine the spread of infectious diseases typically are sensitive to climatic variables. Net climate change-related increases in the geographic distribution of vector organisms (e.g., ticks, mosquitoes, sand flies) of various infectious diseases, along with changes in the life-cycle dynamics of vectors and infectious parasites, would, in aggregate, increase the potential for transmission of many vector-borne diseases in Europe.
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