Cold-waves continue to be a problem in northern latitudes, where very low temperatures can be reached in a few hours and extend over long periods. Accidental cold exposure occurs mainly outdoors, among socially deprived people (alcoholics, the homeless), workers, and the elderly in temperate and cold climates (Ranhoff, 2000). Living in cold environments in polar regions is associated with a range of chronic conditions in the non-indigenous population (Sorogin et al, 1993) as well as with acute risk from frostbite and hypothermia (Hassi et al., 2005). In countries with populations well adapted to cold conditions, cold-waves can still cause substantial increases in mortality if electricity or heating systems fail. Cold-waves also affect health in warmer climates, such as in South-East Asia (EM-DAT, 2006).
22.214.171.124 Estimates of heat and cold effects
Methods for the quantification of heat and cold effects have seen rapid development (Braga et al., 2002; Curriero et al., 2002; Armstrong et al., 2004), including the identification of medical, social, environmental and other factors that modify the temperature–mortality relationship (Basu and Samet, 2002; Koppe et al., 2004). Local factors, such as climate, topography, heat-island magnitude, income, and the proportion of elderly people, are important in determining the underlying temperature–mortality relationship in a population (Curriero et al., 2002; Hajat, 2006). High temperatures contribute to about 0.5 - 2% of annual mortality in older age groups in Europe (Pattenden et al., 2003; Hajat et al., 2006), although large uncertainty remains in quantifying this burden in terms of years of life lost.
The sensitivity of a population to temperature extremes changes over decadal time-scales (Honda et al., 1998). There is some indication that populations in the USA became less sensitive to high temperatures over the period 1964 to 1988 (as measured imprecisely by population- and period-specific thresholds in the mortality response) (Davis et al., 2002, 2003, 2004). Heat-related mortality has declined since the 1970s in South Carolina, USA, and south Finland, but this trend was less clear for the south of England (Donaldson et al., 2003). Cold-related mortality in European populations has also declined since the 1950s (Kunst et al., 1991; Lerchl, 1998; Carson et al., 2006). Cold days, cold nights and frost days have become rarer, but explain only a small part of this reduction in winter mortality; as improved home heating, better general health and improved prevention and treatment of winter infections have played a more significant role (Carson et al., 2006). In general, population sensitivity to cold weather is greater in temperate countries with mild winters, as populations are less well-adapted to cold (Eurowinter Group, 1997; Healy, 2003).