On Thursday, August 24, France's meteorological service Météo-France finally announced that the red heat wave alert would be lifted on Friday for the 17 departments that were still affected. Although temperatures will remain high, between 35°C and 39°C in southern France's Rhône Valley and near the Mediterranean, they should start to fall throughout the southern half of the country. Is this the end of a classic summer heat wave? No, because the episode was exceptional for several reasons.
With its late-season nature, its intensity – more than a hundred temperature records were broken – and its totally unprecedented numbers (over 30°C measured at night in several places), climatologists believe this year's heat wave is a new symptom of climate change and its consequences, which had been predicted for decades.
At each of its briefings, Météo-France did not hesitate to set the heat wave up as an example of what will continue to happen in the first half of the 21st century. "It is highly likely that we will observe more and more episodes of this type, later but also earlier in the season, compared to a reference climatology at the end of the 20th century," explained Lauriane Batté, a climatologist at the French meteorological agency on Tuesday, August 22. "These are the characteristics of the type of events we expect with global warming in the near future, over the period from 2021 to 2050, with stronger heat waves later in the season."
However, this heat wave was not the most intense to have been seen in France. The national heat indicator – the average daytime and night-time temperatures measured at 30 stations across the country – fell short of the absolute record (29.4°C, July 25, 2019). It was not as long as the one in 2003, nor as repetitive as the three episodes of summer 2022. But at a time when nights are longer, the episode made a lasting impression. Since records began in 1947, 2023's heat wave is only the seventh to have been recorded after August 15. All have occurred in the 21st century. And this year's was the most intense.
On Monday (26.63°C), Tuesday (26.93°C) and Wednesday (27.48°C), the national heat indicator beat the previous record for a second fortnight in August, set on August 19, 2012 (26.44°C). This echoed the warnings issued by the Intergovernmental Panel on Climate Change (IPCC), which in its sixth assessment predicted a lengthening season of extreme heat events.
"I'm impressed, but not surprised, because this corresponds to the trajectories predicted, documented and announced by numerous studies over a long period of time," noted climatologist Christophe Cassou (CNRS, Centre national de la recherche scientifique). "And I'm also very worried, because if the atmospheric dynamics that are generating this heat wave had taken place during the climatological maximum, between July 20 and 30, with the additional 2°C warming that we're likely to see around 2050, we'd be opening the door to temperatures of the order of 48-50°C in France. Every year, we're moving a little further into the unprecedented."
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