The term has been used by many media since the publication of an alarming report from the European Copernicus Observatory and the World Meteorological Organization (WMO). In their 2023 report, the two entities are concerned about a new record for days of “extreme thermal stress” broken last year on the European continent. But what exactly does this term mean? Should we be worried about seeing these situations multiply? Obviously yes.
What is a state of “extreme heat stress”?
The report published this Monday does not say how many days Europe suffered “extreme heat stress” in 2023. What we do know is that never has a year been so catastrophic for the human body. Behind this notion of heat stress lies in fact the inability of the human body to maintain a normal temperature due to climatic conditions. In short: the heat, humidity, wind or heat radiation in an urban environment are such that they plunge the body into a state of stress dangerous for health, with the body unable to cool itself. The scientists behind this report estimate that this is systematically the case when the temperature felt exceeds 46 degrees.
And Europe has experienced days of more than 46, particularly in Spain, where records were broken during a torrid summer. Globally, 2023 was the hottest year on record, driven by climate change accentuated by the return of the cyclical El Nino phenomenon. Another alarming phenomenon: the temperature of the oceans, which absorb 90% of the excess heat caused by humanity, has remained at unprecedented temperatures for a year. No wonder that on the surface, the number of days where the temperature exceeded 35 or even 40 degrees continues to increase.
How is this state assessed?
To assess the level of thermal stress suffered by a population, scientists obviously monitor the temperature recorded at a given time in an area. Heat is by far the first element constituting this state of thermal stress but it is not the only one. Indeed, the phenomenon can be accentuated or reduced by certain climatic conditions. Wind, humidity and heat radiation are other factors that can aggravate our body’s state of stress. Just like the duration of an episode of extreme heat, which, if it persists, does not allow our body to regenerate, leading to weakness and fatigue.
In 2023, in addition to heatwaves, the continent has suffered numerous extreme weather phenomena during the year, scientists point out. Two million people were affected by floods or storms, severe droughts affected the Iberian Peninsula and eastern Europe. We can also note that our old continent suffered the largest forest fire in its history, devastating 96,000 hectares in Greece and further accentuating the heat suffered.
Are we all equal in the face of this stress?
Whether we live in Spain or the north of Scotland, we are not all equal when it comes to heat stress. While some countries on the continent are experiencing extreme situations, others are more protected from them, even if the rise in temperatures is perceptible everywhere. According to scientists, Europe’s climate is warming “twice as fast as the global average”, with the global climate already at least 1.2 degrees warmer than before the industrial era. On July 23, at the height of the heatwave, 13% of Europe was experiencing at least one degree of heat stress. Never seen.
Beyond the geographical area, it is also the environment in which we live which has an impact on our state of thermal stress. In urban areas, episodes of extreme heat are thus accentuated by the radiation of the city’s asphalt and the famous “heat islands”. Certain professions, notably people working outdoors, are also more exposed.
What are the risks for our health?
To evaluate the heat stress index, scientists base themselves on the “temperature felt” by residents. For example, we can speak of extreme cold stress when the temperature drops beyond -40 degrees. Extreme hot stress is triggered above 46 degrees. The “normal and ideal” value is reached when the thermometer displays between 9 and 26 degrees. As you can imagine, prolonged exposure to extreme heat is not without consequences on our body, which is not really used to suffocating. According to the researchers behind the report, it increases the risk of disease and is “particularly dangerous for vulnerable people”.
Increased warming in Europe, associated with the aging of the population and the increase in the number of city dwellers, will have “serious consequences for public health”, add the authors of the report. Who even rush to demand action to deal with these situations. “Current measures to combat heat waves will soon be insufficient,” they warn.