Temperatures that should reach or exceed the records for the month of June, and a precocity that alarms climate specialists. France is preparing on Wednesday for an intense heat wave which will extend over the entire territory, from the south to the north. “The three days of Thursday, Friday and Saturday will probably be the hottest in France. Nighttime temperatures will become more and more stifling with minimums often reaching or exceeding the threshold of 20°C” warns Météo France .
This Tuesday, the mercury began to rise and in some regions records records have already been beaten. Like in Cuers, in the Var, with 37.6°C! “This is the highest value for the year 2022, on the scale of metropolitan France, on the main network of Météo-France stations”, warns the public body on Twitter. In the Bouches-du-Rhône, the Marseille Marignane station which was opened a century ago, broke its ten-decade record on Monday afternoon (that is to say, it has never done so hot at this time of year over a period of ten consecutive days) with 36.2°C. The old record dates back to 2003, when the station recorded 35.3°C over these 10 days in June.
Precise definition
“This heat wave remains exceptional because it is very early, the expected temperatures have never been reached at this time since the start of the readings in 1947”, explains Gaétan Heymes, forecaster at Météo France. This exceptional episode is due in particular to a particular meteorological configuration, called a “heat plume”, a heat plume from northern Africa, which encounters a cold drop off the coast of Spain and which facilitates the rise of this very hot air. But “with global warming, the air masses are getting hotter and the annual temperature records are increasing”, underlines Gaétan Heymes. In other words, such a weather event would not have been so likely to occur so intensely (with such temperatures) and at this time of year without global warming.
Since 1947, Météo France has officially recorded heat waves. A term that responds to a precise definition: the average aggregate temperature (i.e. the average of readings from 30 stations throughout the territory) must be greater than 25.3°C for three days and must not drop for a single times below 22.4°C. The last heat wave in the climatic sense dates back to July 2020. “This precise threshold allows us to differentiate heat waves from hot episodes that we may experience elsewhere”, underlines Gaétan Heymes.
Closer, more severe heat waves
Since 1947, Météo France has recorded 43 heat waves. But under the effect of global warming, they have been particularly close in recent years. “There have been three times more in the last three years than in the previous forty years”, explains Météo France. Thus since 2010, we have been able to count 19 heat waves, i.e. almost half of all the waves known since the readings in twenty years. “This shows the much greater recurrence than in the past of these waves”, adds one at Météo France.
On this representation, the size of the bubbles corresponds to the severity of the heat wave, a calculation that combines intensity and duration.
The June study also shows that the heat episodes are also more numerous than before and earlier. Thus the “average temperature” of France in June exceeded 25.3 degrees 5 times between 1947 and 1976 compared to 14 times between 2003 and 2019. Finally, the absolute record for metropolitan France dates from June 2019, with 46°C in Vérargues (Hérault) but it happened at the very end of the month (June 28). “The current heat wave would have been exceptional during the 20th century, it is no longer so today”, explains Robert Vautard, meteorologist and climatologist at the Pierre-Simon-Laplace Institute and specialist in heat waves. heat. “We have events of comparable amplitude in June in 2011, 2017, 2019, and very little before. It is to be feared that this type of event will multiply in the decades to come in France”, he warns.
Heat waves that could last one to two months
“It is almost certain that the increase in the intensity and frequency of extremes of heat as well as the decrease in the intensity and frequency of extremes of cold will continue throughout the 21st century and this, in the world”, recalled on Twitter Christophe Cassou, climatologist at the CNRS and main author of the latest report of the Intergovernmental Panel on Climate Change (IPCC).
France will not be spared. According to the work of Météo France, which is based on the various scenarios of greenhouse gas emissions, at the end of the century, the number of days of heat waves could double or even be multiplied by 10 in the scenario including the more CO2 emissions. “This development is exacerbated in the currently hottest regions, in particular the Mediterranean arc, the Rhône corridor and the Garonne valley. In these regions, heat waves and scorching days may extend over periods longer than a or two months in summer”, warns the organization in a climate change report of metropolitan France.