40 ° C in France! This extraordinary bar only half a century ago is now more and more often exceeded, a symbol of climate change which intensifies summer temperatures with the associated risks.
According to Météo-France, the less and less symbolic threshold of 40 ° C had only been exceeded once in the 1960s and once in the 1970s. In the following two decades, this still rare temperature became more frequent. And in a world that is experiencing the increasingly visible effects of global warming, the 21st century has seen things accelerate.
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Since 2008, at least one measuring station has exceeded 40 ° C each year (except in 2014). And the summers of 2019 and 2020 saw a real festival of 40 ° C, with an extension to the north of the country.
Scientists predicted that the extremes would rise much faster than the average rise in temperature. But are these episodes as intense two years in a row a sign of a spectacular acceleration of warming in France?
A priori no, answer the experts, who note that two years are not representative.
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A coincidence or a trend?
The models do predict that the threshold will be exceeded almost every year, but only " around the middle of the century and rather in the South ", told AFP Robert Vautard, director of the Pierre and Simon Laplace Institute for research in science of the 'environment. So 40 ° C exceeded like that over two years in a row, " it may seem a little surprising, but it's probably a coincidence, " he continues.
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A “ chance ” also for his colleague Christophe Cassou. " But it must be seen as a trend: chance is becoming more likely ", continues the climatologist from the Cerfacs research center in Toulouse.
These peaks are also part of a set which undoubtedly shows the impact of global warming on the summer weather of France.
This is evidenced by the 35 ° C threshold. “ According to Météo-France data on its 30 reference stations, since 2015, the number of times where 35 ° C has been crossed each summer is over 100, whereas this only happened on average 13 times per summer. in the 1960s ”, insists Christophe Cassou.
50 ° C at the end of the century?
It is an indicator " more enlightening than 40 ° C because there is more statistical hindsight " and it " shows that hot summers have been recurring for 5 years ", insists the scientist who participates in the development of the next report climate experts from the UN (IPCC).
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Even without reaching record peaks, a heatwave, with high temperatures at night that do not allow organisms to recover, can have a devastating impact on fragile people. Hence the “ heat wave vigilance ” created after the murderous episode of 2003 which left 15,000 dead in France, an alert intended to warn the population and protect the most vulnerable, such as the elderly.
Above 40 ° C or not, heat waves are also " a threat to certain ecosystems, and to agriculture, heat waves being generally coupled with drought events ", explains Christophe Cassou.
Increased risk of fire
" When it is hotter, the risk of an outbreak (of a fire) is greater, because it takes less energy to set the fire ", explains to AFP Jean-Baptiste Filippi, researcher at the university of Corsica. The humidity of the air and the force of the wind are also essential to assess the fire risk. But on the heat side, beyond the peaks, " it is the duration that is dangerous, " insists the coordinator of the FireCaster program for forecasting fires.
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" The emergency services, very efficient, are on alert to act on all the outbreaks of fire, but it is much more difficult to be as efficient for 10 days ".
Given the projections of climate models, the repetition of 40 ° C still observed this summer may be only a foretaste of the decades to come.