“It’s normal for it to be hot, it’s summer!” “In the South, we have always had 35°C days.” “Seriously, people find out there are heat waves in July?” On the first day of a new heat wave, Monday July 11, annoyed comments were sweating on social networks: it’s hot, yes, but what’s new under the sun?
A few days later, it is clear that this summer 2022, its peaks at nearly 40°C and its two heat waves in less than three weeks, are indeed on the verge of the unprecedented, a heat wave to come. being likely to compete in intensity with that, historic, of 2003.
But before the verdict of the mercury, franceinfo draws up an observation: we are experiencing summers of a new kind, both different from what we have known in the past, and representative of what awaits us. A summer that pushes the cursor back a little more “the extreme”of “the normal” and “of possibilities.”
Weather extremes ‘boosted by climate change’
Didn’t we burn our thighs on plastic chairs when we were children? “To say that nothing has changed, the oldest cite, for example, the heat wave of 1976, or that of 1983. We tend to remember a particular heat wave event and generalize it“, notes the climatologist Christophe Cassou. In reality, “we have very little climatic memory”, he notes on the phone from Toulouse where, on Tuesday, the thermometer peaked at 37 ° C, nine degrees above seasonal norms for the pink city. The habit of warmer conditions already skews our relationship to the climate. “For example, we will have the impression that the summer of 2021 was rather cool, whereas it is a summer that would have been hotter than normal in the 1980s”, he continues.
If the human being cannot always trust his memory, the figures are formal: since 1947, France has experienced 44 heat waves at the national level and is now going through a 45th in mid-July. Above all, there have been more since 2006 than during the previous six decades (as shown in the following graph). “Heat waves have always existed, but they are boosted by climate change”insists one of the IPCC experts. “They are more frequent, more intense and longer.” It is not rare, from now on, to count several of them per summer when, formerly, several years separated two events. Like in 2019, when the South first suffocated at the end of June, before the North suffered its heatstroke a month later. That year, Vérargues, in the Hérault, recorded the new national heat record (June 28): 46°C. And Paris beat its previous record (July 25) by more than two degrees: 42.6°C.
“Until recently, 43°C was inconceivable in mid-June in France. We know the rest”, commented on Twitter earlier this week the meteorologist François Jobard. “The 1976 heat wave marked the spirits, but we did not exceed 38 ° C at the end of June”, he recalled. In the 1960s, the 40 ° C threshold was actually exceeded only once (in 1968 in Aquitaine) and another in the 1970s (in 1975 in Corsica), according to Météo France, quoted by AFP . In 2022, summer had not officially started when France was already breaking the record for its earliest heat wave (between June 16 and 18), with a thermometer showing a boiling 43.4°C in Pissos, in the Landes.
Even before the solstice, 35 absolute records fell in France, listed the MétéoCiel site. “VSExtremely high temperatures tend to appear earlier in the season [cette année, il a fait 34 °C en mai à Tarbes]to generalize to regions that had not yet known them and to linger later in the season”, meteorologist Matthieu Sorel confirmed Monday, July 11, during a press briefing from Météo France.
“Climate change favors hot extremes, which warm faster than the average temperature”explains Christophe Cassou. “For one degree of average temperature warming, the hottest temperatures take 1.5 degrees.” However, the “normal”, too, continues to climb.
The “normal” is warmer, too
Another particularity of this summer 2022? The first heat wave occurred before Météo France updated its “normals” of the season. This value, included in particular in weather reports, is reviewed every ten years, under the rules of the World Meteorological Organization (WMO). To define them, the agency has based itself since June 28 on the decades 1991-2020, against 1981-2010 previously. Gold, the temperatures observed since the beginning of the summer remain well above these new values who, because they are “representative of a climate centered on the years around 2005 (…) will still present a slight bias as climate change, and the associated rise in temperatures, has accelerated in recent decades”recognizes Météo France.
If the average temperature in France has warmed up by 1.7°C since 1900, “over the past ten years (…) the rise has reached 0.6°C and marks the strongest increase observed between two decades in France”, notes the meteorological agency. These new “normals” reveal for example that Lille (Nord) now knows the old climate of Rennes (Ile-et-Vilaine), Strasbourg (Bas-Rhin) and Dijon (Côte-d’Or) that of Lyon (Rhône) and Le Mans (Sarthe) that of Bordeaux (Gironde).
Why change?
️ 1981-2010 normals representative of the average climate over a period around the 1990’s no longer corresponded to the “current” climate in a context of climate change.
— Meteo-France (@meteofrance) June 27, 2022
According to the climate simulations of the Drias project (pages 32 and 33 of the PDF document), carried out by several French laboratories, the seasonal averages will in the future all show a warming “more severe in summer and less severe in spring”. The temperature difference estimated in summer between the years 2021 and 2050 increases by another degree (in median value) in a scenario of drastic reduction in greenhouse gas emissions and by 1.3°C (still in value median) for the other two emission scenarios. Or the conditions for a short-term increase in extreme phenomena, driven by these warmer averages.
On the horizon, ever more worrying “possibles”
“Climate change intervenes on the field of possibilities”, summarizes the climatologist Christophe Cassou. For him, it is by speaking of probabilities that we best represent the action on our climate of the change that is taking place. “With a global warming of 1.1°C or 1.2°C compared to the pre-industrial era [le niveau de réchauffement actuel à l’échelle mondiale], the heat wave of June 2019 had a one in fifty chance of occurring”, explains the specialist. “At 1.5°C of global warming – which we expect with certainty before 2040, and very probably even in the 2030s – we go to a one in ten chance of experiencing such an event. At an additional 2°C – this where we are heading towards 2050 or 2060 if we rely on the public policies currently in place – it is a one in four chance. At this level of probability, the 2019 heat wave will become the normal climate in summer.
This slider “of possibilities” continues to shift into the red. Even in the dark, and beyond: colors that made internet users shudder when astonishing maps displaying temperatures over 45°C for mid-July over a major part of France circulated on social networks .
Another GFS run with simply unprecedented heatwave over western Europe: 48°C in France, 43°C in UK…
And now at day 7-8 time range.
The point here is not that this would be a likely outcome, but rather that a reliable global model can even simulate such a scenario. pic.twitter.com/zUKYqLn7A9
— Mika Rantanen (@mikarantane) July 9, 2022
Coming from a scenario among hundreds of others, and produced by a model called “GFS”, this map was not a forecast, however, the specialists hastened to recall. At the same deadline, “another scenario, with the same probability, showed 28°C”, recalls Christophe Cassou. But if, “Taking a pattern in isolation ten days out makes no sense in terms of predictability, the fact that a pattern can produce such high temperatures – whether they come true or not – gives an indication of what maybe the climate today”, he raises.
“The models have the same biases and the same errors as in 2000, but we have simulations that give higher temperatures than what we had seen so far”, continues the climatologist. If not a reliable forecast, these simulations therefore constitute a warning: this summer 2022 will be a worse day than “normal” in our minds. He will have left the memory of a summer “costs”.