| What lessons can be learnt from the exceptionally long
and severe heat wave experienced in Europe in 2003?
First, that these heat waves can be responsible for a dramatic excess
mortality: certainly more than 50 000 excess deaths for Europe in August
2003. The consequences of the heat wave were probably underestimated in
many countries, at least those based on the first estimates. This excess
mortality affects vulnerable groups, particularly those who are old or
ill. Identification of risk factors is a priority if the necessary prevention
actions are to be implemented.
There is no doubt that age is one of the main risk factors, particularly
for those over 75 or 80 years, but age-associated factors are also very
important. Case-control studies carried out in France found that loss
of autonomy and social isolation played a major role in the risk factors
for the elderly, as did living directly below the roof of a building,
in a heat island, particularly in cities.
These heat waves make us question the ways in which our societies are
changing, and how we organise them. The main challenge for the future
is the aging of the population, particularly the growing number of very
old people, and how they live in our cities (in terms of housing and
social integration) or in nursing homes (quality of healthcare and management).
The next few decades will be marked by the convergence of three events
that will transform the exceptional circumstances of 2003 into a recurrent
risk that must be considered as a priority in our health policies.
These three events are population trends, air pollution and global warming.
- Population trends: as life expectancy increases, there will be increasing
numbers of highly vulnerable people aged 80 years and over. The 25th
International Population Conference, held in July in Tours (France),
reported the human population is aging worldwide and that the proportion
of those aged over 60 will double in the next 30 years. This aging trend
is most marked in industrialised countries, particularly in Europe.
- Air pollution played an undeniable role in 2003. The respective roles
of temperature and ozone in the excess mortality are difficult to assess
. The relationship between ozone pollution and excess mortality was
estimated to be between 3% and 85% in nine French towns . The reason
for this high heterogeneity between towns remains unclear, and demands
- Analysis of long term meteorological trends carried out in recent
years underlines that global warming is a reality, and that more heat waves
are highly likely to occur in the future.
It will no longer be possible for us to exclaim surprise at these climatic
events and their consequences. We must reinforce policies for forecast,
alert and prevention.
Nowadays, most European countries have implemented surveillance and
alert systems. None of these systems can predict the occurrence of these
events with any certainty, and the expected consequences of these heat waves,
in terms of duration, intensity and populations affected, are difficult
to estimate precisely. In other words, the positive predictive value
of an increase in temperature versus mortality is low when analysing
the historical series of heat waves and mortality. It is difficult to
choose the sensitivity of the alert threshold. If the biometeorological
indicators chosen are too high, this could result in inappropriate identification
of risks linked to less severe heat waves. We should not rely totally
on any alert system, whatever its sophistication.
The objective of the alert system must be to set up strengthened action
and prevention measures, based on sound advice for vulnerable populations.
Nevertheless, the uncertainties about the efficiency of these actions,
launched just before or during threat of a climatic event, highlight
the need to consider the problem in depth, so that we can prevent future
risks, independently from any alert system.
This is why it is important to analyse the determinants of excess mortality
during heat waves. It addresses our capacity to respond the needs of vulnerable
persons: town planning needs to come up with solutions to reduce the
effects of heat islands, and we ourselves need to strengthen social bonds
with vulnerable people, particularly elderly and dependent people, and
to improve the quality of the facilities and the skills of the staff
who care for these people in hospitals and nursing homes.
Some may have fatalistically viewed the 2003 heat wave as a natural event
whose effects were inescapable, but the epidemiological, environmental,
and sociological study reveal the ways in which deficiencies in the care
of these vulnerable populations and the lack of control in town planning
increase the health risks linked to weather conditions.
Once again, surveillance programmes are invaluable for anticipating
and managing those risks. A concerted action to deal with climatic risks
at the European level is urgently needed.