IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability Effects of patterns in heat and cold stress

Episodes of extreme heat or cold have been associated with increased mortality (Huynen et al., 2001; Curriero et al., 2002). There is evidence of recent increases in mean surface temperatures and in the number of days with higher temperatures, with the extent of change varying by region (Karl and Trenberth, 2003; Luterbacher et al., 2004; Schär et al., 2004; IPCC, 2007). This increase in heatwave exposures, where heatwaves are defined as temperature extremes of short duration, has been observed in mid-latitudes in Europe and the USA. Individual events have been associated with excess mortality, particularly in the frail elderly, as was dramatically illustrated in the 2003 heatwave in western and central Europe, which was the hottest summer since 1500 (Luterbacher et al., 2004; Chapter 8, Box 8.1).

In general, high-income populations have become less vulnerable to both heat and cold (see Chapter 8, Section 8.2). Studies in Europe and in the USA of mortality over the past 30 to 40 years found evidence of declining death rates due to summer and winter temperatures (Davis et al., 2003a, b; Donaldson et al., 2003). Declines in winter mortality are apparent in many temperate countries primarily due to increased adaptation to cold (Chapter 8, Section (Kunst et al., 1991; Carson et al., 2006). However, the mortality associated with extreme heatwaves has not declined. The 25,000 to 30,000 deaths attributed to the European heatwave is greater than that observed in the last century in Europe (Kosatsky, 2005). Analyses of long-term trends in heatwave-attributable (versus heat-attributable) mortality have not been undertaken.