Heat and health

Temperature-mortality relationship in 15 European cities

Note: Figure shows relationship between daily maximum apparent temperature (Barcelona: mean apparent temperature) and natural mortality (blue) and 95% confidence interval (grey).

Data source:

Baccini M.; Biggeri, A.; Accetta, G.; Kosatsky, T.; Katsouyanni, K.; Analitis, A.; Ross Anderson, H.; Bisanti, L.; D'Ippoliti, D.; Danova, J.; Forsberg, B.; Medina, S.; Paldy, A.; Rabczenko, D.; Schindler, C. and Michelozzi, P., 2008. Effects of apparent temperature on summer mortality in 15 European cities: results of the PHEWE project. Epidemiology 19 (5).

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Past trends

Many epidemiological studies have quantified the impact of temperature on daily mortality. In all cities in Europe mortality increases over a certain threshold of temperature. This threshold is location-specific (see Figure 1).
The estimated change in mortality risk per degree temperature increase over the location- specific threshold ranges from 0.2 to 5.5 % (Kovats et al., 2006; Baccini et al., 2008).
Most European countries have between 5 and 30 % higher death rates in winter than in summer. Winter-related mortality in many European populations has 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: improved home heating, better general health and improved prevention and treatment of winter infections have played a more significant role (Carson et al., 2006). More than 70 000 excess deaths were recorded in 12 European countries from June to September 2003, compared with the 1998 to 2002 average (Robine et al., 2007). Although this increase cannot be entirely attributed to the heat waves in 2003, in the absence of any other explanatory factors, most of these deaths are likely to have been caused by the several heat waves in that year. The timing, intensity and duration of heat waves have been shown to influence the amount of mortality. Impacts of heat waves characterised by longer duration were from 1.5 to 5 times higher than for short heat waves (Matthies et al., 2008).
Major heat-wave events are also associated with other health hazards such as air pollution, wild fires, water, food and electricity supply failures, which also have implications for public health action. The combined effect of heat waves and peaks of air pollution due to ozone or particulate matter with a diameter under 10 micrometer (PM10) increases mortality. There is growing evidence that the effects of heat-wave days on mortality are larger when ozone or PM10 levels are high, particularly among the elderly (75-84 years). In nine European cities the total daily number of deaths in the age group 75-84 years increased by 10.6 % during heat-waves when ozone levels were low but by 16.2 % when ozone levels were high; corresponding figures for PM10 were 10.5 % and 14.3 % (Analitis and Katsouyanni, in press). The mortality increase due to the combined effect of heat and air pollution can be reduced by decreasing exposure to ozone and PM10 on hot days.
Cold waves continue to be a problem if very low temperatures are reached in a few hours and extend over long periods. Accidental cold exposure in temperate and cold climates occurs mainly outdoors, among the socially deprived (alcoholics, the homeless), workers, and the elderly (Ranhoff, 2000). Living in cold environments in polar regions is associated with a range of chronic conditions in the non-indigenous population as well as acute risk from frostbite and hypothermia (Hassi et al., 2005). In countries with populations well adapted to cold conditions, cold waves can still cause increases in mortality if electricity or heating systems fail.

Projections

Heat-related morbidity and mortality is projected to increase. Estimates of heat mortality have been made in several national assessments, using different climate scenarios and population and adaptation assumptions. In the United Kingdom, annual heat-related deaths are expected to increase from about 800 in the 1990s to about 2 800 in the 2050s and about 3 500 in the 2080s in the medium-high scenario. Annual cold-related deaths decrease from about 80 300 in the 1990s to about 60 000 in the 2050s and 51 200 in the 2080s in the same scenario (Donaldson et al., 2001). In Germany, a 20 % increase in heat-related mortality is projected. This increase is not likely to be compensated by reductions in cold-related mortality (Koppe et al., 2003). In Portugal, an increase in heat-related mortality from a baseline of 5.4 to 6 per 100 000 to a range of 19.5 to 248 per 100 000 by the 2080s is projected (Dessai, 2003).
For the EU-27 Member States, the PESETA study projected almost 86 000 net extra deaths per year in 2071-2100, compared with the 1961-1990 EU-25 average, for a high emissions scenario (IPCC SRES A2) with a global mean temperature increase of 3 ^oC (EC, 2007). These results are preliminary, assume no physiological adjustment, and do not separate out the impact of non-climate changes (socio-economic changes in age structure or population movements). The study is based on assumptions of a mortality-temperature relationship that does not take into account the differences between the Mediterranean and northern European countries.