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Exposure to extremely hot or cold temperatures has a direct impact on our health, in terms of mortality and the use of healthcare. Faced with climate change and the considerable variations in temperature experienced by France, the study of the evolution of temperatures and the number of associated deaths has become essential. In its report, Santé Publique France demonstrates that the temperature changes that have taken place over the past 45 years have resulted in an overall acclimatization of the population to a new climate. However, there remains a significant impact of high heat on mortality.

Climate change and mortality

Exposure to unusually hot or cold temperatures increases the risk of mortality. This is explained by the fact that after exposure, for example to extreme heat of the order of 30°C, the body makes considerable efforts to maintain a stable body temperature (at 37°C). It is a strong solicitation of the organs which, in vulnerable people, can induce cardiac or respiratory failure. In France, between 2000 and 2010, 13,855 deaths were caused by extreme heat.

In a recently published report, Public Health France reports the results of its study conducted between 1970 and 2015 on the evolution of the relationship between temperature changes and mortality. For this, the authors of the report relied on temperature and mortality data collected daily in 18 urban areas of metropolitan France over a period of 45 years.

Extremely hot weather deaths doubled in 45 years

The results obtained highlight contrasting changes in mortality risks according to temperature levels:

• For extremely cold average temperatures (-7°C), the risk of death was lower in the 1970s compared to the 2010s;
• For extremely hot average temperatures (28°C), the associated risk of death was higher in the 1970s compared to the 2010s;
• For non-extreme temperatures, the associated mortality risks have remained stable over the past 45 years.

However, the changes observed in terms of risks are not reflected in the number of deaths observed. In effect :

• Deaths attributable to the coldest temperatures have remained stable since the 1970s. They constitute 0.6% of total annual mortality;
• Deaths attributable to the hottest temperatures have doubled since 1970, from 0.11% to 0.23% of total mortality in 2010. This is because, although the risk of death from hot temperatures is decreasing, the number of days when these extremely hot temperatures are observed is increasing. Thereby, the reduction in risk does not compensate for the increased exposure to high heat.

Prevention to be continued and reinforced

The Public Health France report demonstrates possible acclimatization of the population to a new climate. This acclimatization can be explained in different ways. It can be linked to a improved socio-economic conditions (improvements in working conditions, democratized access to air conditioning systems, etc.) and medical. The introduction of the national heat wave plan in 2004 did not mark a break in the number of deaths linked to very hot temperatures but could have contributed.

It is nevertheless essential to continue efforts to reduce the impact of cold and hot temperatures on mortality. Indeed, climate change induces an increase in temperature values ​​as well as greater variability. Adapting to these rapid temperature changes is a major public health issue. It is estimated that 30% of mortality attributable to high heat between 1990 and 2018 is attributable to climate change.

Public Health France proposes 3 axes of prevention of extreme temperatures and adaptation to the climate:

• Improving the overall state of health of the population in order to improve its capacity for thermoregulation;
• Action on living environments and work organizations to limit exposure to extreme temperatures;
• Continuing to organize a coordinated response to the most extreme events.

Alexia F., Doctor in Neurosciences

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