They can be counted on the fingers of one hand. For the fourth time since the entry into force of the system in 2004, 12 departments have just been placed on Thursday on heatwave red alert, announced Prime Minister Elisabeth Borne. So far, 23 departments were on orange alert. 41°C could be reached locally, while temperatures will fluctuate between 36°C and 40°C. The record of 46°C recorded in Vérargues (Hérault) on June 28, 2019 should not, however, be beaten.
Fatal heat stroke
Extreme heat can be dangerous for the human body, whose temperature will rise and will dehydrate by sweating. “The vessels dilate, we have hypotension, and to fight there is an important sweating system which starts to regulate the body’s temperature”, indicates to L’Express Evelyne Chartier, general practitioner. By being careful not to do physical activity and to hydrate well, “people without pathology and who are neither babies nor elderly people do not risk much”, she adds.
But in a situation where extreme heat has set in over time, “the thermal regulation mechanisms – perspiration, breathing and radiation – are overwhelmed”, explains to L’Express Jacques Battistoni, general practitioner and president of the MG France union.
Indeed, the body regulates itself between 37°C and 37.5°C. By regulating itself, it expends energy, it gets tired. “We can endure a certain time, but after a while the body is exhausted, abounds the general practitioner. Sweating only lasts a while, you cannot sweat forever”.
“So we can die of heat, of heat stroke, what we call malignant hyperthermia, when the core temperature rises too much, the regulators no longer work, we see organ failure, but even before this stage, it is at the cerebral level that we are affected”, he adds. An assertion which was sadly verified during the heat wave in 2003 which caused the death of 20,000 people in France, and approximately 70,000 in Europe.
Some people more vulnerable than others
However, we are not all equal in the face of heat. Several categories of people are more vulnerable, such as the elderly. Others may die from a different cause, but triggered or related to heat.
“The older we get, the more the perception of heat changes, we are less aware of body temperature and, at the same time, the sweating mechanisms are less efficient and we lose the feeling of thirst”, underlines Jacques Battistoni . Infants also cannot interpret their needs, which makes them more vulnerable, “especially since their immune system is still immature”.
People with chronic diseases (heart, kidney, respiratory failure) must also protect themselves more from heat. And especially those who take treatments that disrupt the mechanisms such as drugs against hypertension. To fight against the heat, “the body gets very tired, especially when there are pre-existing pathologies”, abounds in the World Rémy Slama, environmental epidemiologist and director of the public health institute at the National Institute of Health and Medical Research (Inserm).
Can the body acclimatize over time?
Especially since humanity will most certainly have to get used to such heat waves linked to global warming. The latter will, according to experts, become more frequent and more intense as the warming intensifies. But can the body adapt to such heat? “I think because he always adapts but there are limits,” says Evelyne Chartier. But for Jacques Battistoni, while the body could eventually adapt to warming degree by degree, a uniform increase, the problem with extreme heat is that it “is not regular or linear”. Populations experience heat waves with increasingly high peaks that punctuate long periods of normal temperatures. The body does not have time to get used to the extreme temperature.
Thus, man will further adapt his way of life, his habitat or his clothes to be able to live in difficult temperature conditions. “The Berbers are covered from head to toe in the desert”, notes Evelyne Chartier. In Algeria, houses are painted white to reject heat.
At World, Rémy Slama explains that the phenomenon has been studied in several cities such as New York where the temperature “was much more damaging at the beginning of the 20th century than at the beginning of the 21st.” But this observation is not linked according to him to “physiological adaptation of New Yorkers, but more likely to a societal adaptation to higher temperatures.” Air conditioning has thus become widespread in the mores of the inhabitants of the American city. “In any case, it is not clear that the organism adapts to higher temperatures, whether on the scale of a lifetime or that of a small number of generations, or even several tens of ‘years,’ he concludes.
Can we reach 50°C in France?
According to Jean Jouzel, climatologist, former vice-president of the scientific group of the IPCC, and member of the Academy of Sciences, contacted by L’Express, “the heat causes the death of 3000 people in Europe each year,” and “we could exceed the 100,000 deaths per year linked to global warming in the second part of the century with a warming of 3 degrees”. He warns against such a scenario that “certain regions of the planet would become unlivable, which means that they can no longer have normal activities outside.”
In July 2021, an unprecedented heat wave spread across Canada, triggering heat wave alerts in areas where millions of people live. Experts believe it was caused by global warming. An all-time high of 49.6°C was recorded in the town of Lytton, which was subsequently 90% destroyed in the flames of a fire triggered by the heat wave. A temperature above 4°C from the previous national record. Nearly 700 people in Canada, and at least 16 in the United States, died suddenly from the heat last summer. Because if we can die of cold, we can also die of heat.
If the problem seems far away in France, a situation like the one experienced by Canada in 2021 remains a possibility. “Imagine that we beat a record with a margin of 4 ° C, we would reach 50 ° C too, explains to L’Express Samuel Morin, researcher at the National Center for Meteorological Research (CNRM). If records will certainly not be beaten in the next few days, let’s not forget that it’s only June…