2023-09-04 12:00:30
Record heat all over the planet, warnings from the UN and monster fires, especially in Canada…
The summer of 2023 is already facing oppressive temperatures, while many European countries have seen the thermometer climb above 40 degrees for several days.
Twenty years after the terrible heat wave of 2003, what do we know about the effects of these meteorological episodes on our health?
2003, the summer of awareness
Daily meteorological conditions such as temperature and humidity have a role on our health that has been known for a long time, but which became apparent to the general public during the heat wave of summer 2003: temperatures above 35°C were then observed by two-thirds of Météo France stations between 1is and August 18; the maximum and minimum temperatures were the highest since 1950; the nighttime temperature remained high, above 25°C in Paris for two consecutive nights, preventing the body from recovering at night from daytime heat stress, all this in conjunction with high levels of ozone pollution.
On August 10, when the heat wave had already started for more than a week, an emergency doctor from a major Parisian hospital, Dr. Patrick Pelloux, sounded the alarm in the media, announcing that the emergencies were overwhelmed and working in impossible conditions; he spoke of a hecatomb, citing the figure of around fifty deaths due to the heat wave. Funeral services also indicated that they were outdated. Refrigerated halls of the Rungis market were requisitioned to serve as emergency mortuary rooms. On August 13, the white plan, which allows the requisition of doctors and hospital beds, was launched by the authorities in Île-de-France.
On August 17, the Ministry of Health denied the hypothesis of 5,000 excess deaths then announced by Dr. Pelloux, before indicating on the 18th that a figure of 3,000 to 5,000 was ultimately plausible. The Director General of Health was forced to resign. On August 20, a group of funeral directors estimated that the number of excess deaths since the beginning of August was around 13,000, a number that the government could not confirm, calling for “caution “.
In fact, the excess mortality in August 2003 compared to the average of the previous years was around 15,000 deaths for the whole country. Ile-de-France and many cities were affected, while the urban areas of Lille and Le Havre were spared by the excess mortality. On a European scale, the number of deaths caused by the heat wave of the summer of 2003 would be around 70,000, which makes it one of the deadliest of those whose effects are documented.
A loss of life expectancy
The magnitude of the effect seems to have depended on many environmental factors (urban heat islands, density of green spaces, air conditioning, etc.), social and behavioral. It was not just a question of a very short-term shift in mortality (this is what would have happened if only very sensitive populations or populations affected by other pathologies had been affected by the heat wave, and if the excess mortality during the heat wave had been compensated for in the following weeks by lower mortality. Such a lower mortality compared to the average was not observed in the months following the heat wave). A real decrease in life expectancy has therefore taken place.
The 1976 heat wave caused 6,000 excess deaths nationwide. All these deaths do not correspond to “heat strokes” or severe dehydration, and are therefore not identified as being due to heat by death certificates (the situation is the same for air pollution and most of the other environmental factors). Many of them correspond to what can be seen as the decompensation of underlying pathologies (cardiovascular, respiratory, renal, etc.): the heat wave is the additional factor that triggers the occurrence of death from multiple causes.
Heat waves: long underestimated health consequences
In France, this heat wave confirmed or revealed several fundamental things. The first is that heat kills and can do so significantly – this “environmental” factor was not really on the radar of health and environmental authorities. No health agency or state service linked to health was then, in France, really responsible for “monitoring” the occurrence of a heat wave. There was no coordination set up between Météo France and a health agency, a situation which has since changed.
The second is that the heat wave does not only affect very fragile and already hospitalized subjects, on the contrary. Three quarters of deaths occurred at home, not in hospital, probably because subjects already hospitalized were well monitored and hydrated by medical personnel. The fight against the heat wave is, in our country, a problem of prevention – as long as we do not weaken the healthcare system. The situation follows the same logic for people living in retirement homes. Alfred Spira’s team has shown that, among elderly people living in institutions, the effect of the heat wave was more marked in those in good health than in those who had less good health before the onset of the heat wave.
Third lesson: the authorities are therefore not able to monitor the mortality of the population in real time. It is the emergency services, the police, the fire brigade, the funeral services, which are sounding the alarm, with fragmentary estimates and often, logically, far from reality. The situation is different in the United Kingdom where, since the 17e century, mortality data are available within less than a week. A dozen years later, France does not yet have the means to monitor deaths exhaustively on a territorial scale in real time or with a lag of the order of a week; the electronic death certificate project could improve the situation. A death monitoring system called Sursaud, has been set up by Santé Publique France and allows rapid reporting of mortality data for around 80% of the population, in addition to the centralization of data from 600 emergency services.
Faced with the weather, all populations are not equal
The influence of meteorological conditions is not limited to extreme episodes, but is also observed during seasonal fluctuations. Thus, using a time series approach, we find a U-shaped relationship between temperature and mortality, with increased mortality at the coldest and hottest temperatures.
The thermal optimum (generally located between 15 and 25°C), and therefore the thresholds from which the risk of death increases, varies according to the populations: the populations of southern Europe, thus, are more sensitive to the effects of cold than that of the North, and those of the North to the heat. This is probably explained by an adaptation of each population to the local climate, through lifestyles that are more or less effective in protecting against heat or cold, in terms of heating, insulation, protection against the sun, of solidarity…
This does not mean that we can resist everything. When we describe the influence of temperature on mortality according to the distribution of temperatures in each city, we realize that the inhabitants of American cities and countries like Australia begin to suffer (in terms of mortality) from heat when it reaches the 10% hottest temperature. In Spain, on the other hand, the risk of mortality increases much earlier, as soon as the median temperature (that observed or exceeded half of the summer days) is reached. We will come back to the question of adaptation to heat waves. Furthermore, the effect of temperature on mortality is modified by humidity, which tends to amplify it.
The effects of temperature on health
The mechanisms by which temperature influences health are on the one hand biological effects on the organism, on the other hand effects on the environment and finally on behaviour.
Regarding the environment and behavior, the cold can, for example, promote poisoning by carbon monoxide from boilers, trauma related to ice storms, as well as the transmission of certain epidemics due to viruses that survive better in cold and dry weather. typical of winter.
The more direct biological effects concern the cardiac, respiratory, endocrine, immune and nervous systems. Effects of meteorological factors on pregnancy outcomes are also plausible. We know in particular that low atmospheric pressure is a risk factor for low birth weight; this has been known for a long time, following the finding that children born in the state of Colorado (much of which are at altitude, therefore at lower atmospheric pressure than at sea level) more often have a low birth weight. An effect of meteorological parameters, and in particular temperature, on the risk of premature birth, has also been recently suggested.
A word about the prevention of the health effects of temperature: unlike the fight against air pollution, in which improving the quality of the environment is difficult to circumvent, we can limit a large part of the effects of temperature on health by simply protecting the body, without necessarily affecting the environment. In the case of the fight against the heat wave, cooling the body for a few hours a day is enough to mitigate a large part of the health effects. The preventive measures recommended go in this direction (hydrating, limiting physical exercise, going out less during the hottest hours).
It is striking to note that, in our country at least, most of these measures correspond to individual recommendations; there are apparently no measures intended for local authorities today. However, these have many levers in their hands: open swimming pools for an extended period and at a lower cost, water the streets, make air-conditioned places more accessible… Such measures are complementary to individual recommendations, and could. There is a lack of hindsight on the measures that are the most effective, but some cities have started to adopt “heat wave plans” (like Grenoble), beyond the National Heat Wave Plan. These measures seem overwhelmingly focused on short-term prevention, while longer-term actions could also be useful to make our societies more resilient to heat waves: greening cities more and increasing the reflection of floors and roofs, part of the solutions implemented abroad, and providing local authorities with a full update on the range, effectiveness and cost of the various options available to them would be important.
Adapt to climate change?
Climate change is likely to lead to an increase in the frequency of such extreme climatic events (hot or cold waves, storms). A tendency of the French population to tolerate heat waves better, since 2003, has been observed. This adaptation is probably explained by changes in behavior towards the elderly and by other changes in our society, rather than by physiological processes. It does not mean that societies are or will be able to fully compensate for the effects of climate change through an increase in the frequency of heat waves; above all, it is very probable that they will not all be able to do so.
Initial elements suggest that the ability to adapt – the resilience of societies, of urban areas – in the face of heat waves does indeed vary from one region to another. This work thus suggests that, during the period going from 1993 to 2006, the cities of Japan or the United States became less sensitive to the heat wave, whereas this is apparently not the case of the cities of the United Kingdom. . Data covering the entire XXe century are especially available for New York City. They indicate that the effect of a temperature of 29°C on a given day on mortality corresponded to an increase in mortality of about 43% in the years 1900-1909 (with a 95% confidence interval ranging from 37 at 49%). This effect was divided by five, falling to 9% (confidence interval, between 5 and 12%), in the years 2000-2009.
Air conditioning will not be the solution
This significant improvement in resilience in New York during the 20e century seems like good news. It has however, at least in part, been obtained by the generalization of air conditioning, transport in private vehicles (also air-conditioned) including over short distances. Nearly 90% of American homes are air-conditioned, and air conditioners consume energy (the production of which is a source of greenhouse gases), and have long emitted gases from the CFC family, which are thousands of times more powerful than carbon dioxide in terms of contributing to the greenhouse effect, in addition to damaging the ozone layer.
[À lire aussi Le paradoxe des climatiseurs qui réchauffent la planète]
CFCs were banned from US air conditioners in the mid-1990s, but many of those produced up to 2010 still use gases from the HCFC family, which are also strong contributors to the greenhouse effect.
If what makes American society increasingly resilient to the heat wave is also what contributes to making it the one that emits the most greenhouse gases per capita, then there is reason to fear that the “model” cannot be transposed to the scale of the planet…
This text is taken from Rémy Slama’s book, Evil from without, The influence of the environment on healthpublished by Quae.
Rémy Slama, Director of Research in Environmental Epidemiology,, Inserm
This article is republished from The Conversation under a Creative Commons license. Read the original article.
How the heat wave affects our health
couple Rémy Slam, Inserm
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