Epidemiologist, Mathilde Pascal is in charge of the “climate change and health” project at Public Health France.
What data are available on the impact of heat peaks on mortality?
For a long time, these risks were little studied. The studies began when there were deadly and significant heat waves, first in the United States and particularly in Chicago, in 1995, then more widely from 2003. From this historic heat wave, responsible of 70,000 deaths in Europe, there have been many studies all over the world on the links between temperature and mortality, with enormous progress in terms of methods.
The risk of death related to temperature rises is not easy to model but we know that it does not increase in a linear fashion. For temperatures that are not extreme, and that occur frequently, the excess risk of death is low, even if overall it is not negligible.
For exceptional temperatures such as we are currently experiencing, the risk of death increases sharply, mainly in the three days following the peak. At this level, an extra degree can make a significant difference in risk.
Of course, some populations are particularly vulnerable: those whose thermoregulation is less effective due to their age (young children, the elderly), a chronic pathology or the taking of certain medications. There are also occupationally exposed individuals or the homeless. But, at a certain level of temperature, we can consider that the vulnerable population is everyone.
The most specific effect of high heat on the body is hyperthermia due to failure of the thermoregulation system, which is a vital emergency. But it’s not the only one. The scientific literature clearly shows that there is also an increase in respiratory, cardiac and renal problems… In fact, heat-related deaths can be of different natures. More recently, we have begun to study the consequences for workers, and in terms of mental health. A worrying point is the lack of studies on the effects of heat waves on pregnancies, especially at their beginning and end. It is accepted that heat peaks promote prematurity and low birth weight, but there are still few data in pregnant women.
Do the preventive measures put in place after the 2003 heat wave make it possible to reduce the mortality from these episodes?
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