Christophe Cassou, climatologist at the CNRS and one of the main authors of the report of the Intergovernmental Panel on Climate Change (IPCC) published in August 2021, explains the occurrence of the current heat wave and reacts to the prospect an even greater warming than expected in France, with the effects “hard to imagine”.
France is experiencing high temperatures this week. The thermometer flirted with 34 degrees Tuesday in the Southwest. Is it exceptional?
Yes, it is very rare to exceed 30°C during the day in October, but also not to drop below 20°C at night, as in Toulouse on Tuesday. This is 10°C above normal weather. Temperatures like 34°C are extreme values for October. Many ten-day records, that is to say over periods of ten days, have been beaten. At this time of year, monthly averages are less relevant because October is the month with the greatest temperature changes between the beginning and the end of the month. What is also exceptional is the persistence of such high temperatures throughout the week.
This late heat wave is linked to an atmospheric dynamic that naturally favors warm conditions: south-southwesterly winds linked to a very vast depression that covers the entire North Atlantic, between Greenland and the Azores, which carries hot air from the Maghreb to Western Europe. This configuration is classic but now, with climate change, it is accompanied by ever higher temperatures.
This episode prolongs a particularly hot year…
We tick all the boxes of the effects of climate change: the increase in the frequency of heat waves – we are at the fifth this year –, but also their intensity, their duration and their change of season. We reached strong heat from May until October. With climate change, the summer season is getting longer so that autumn starts later. Winter is getting shorter and ending earlier. In the middle of the century, exceeding 30°C in October will no longer be exceptional.
Is there an acceleration of climate change?
No, we are following the same warming trend: we have been gaining 0.36°C per decade for thirty years in France. But we observe an intensification of the impacts. For each additional tenth of a degree of warming, the effects of climate change are multiplied. With the current level of warming (+ 1.7°C since 1900 in France and + 1.2°C worldwide), we have already experienced a catastrophic summer. Today it can still be considered rare, but around 2050 it will become classic. It makes us feel what a global warming of 2°C expected around 2050 will look like, considering the trajectories of current emissions and the public policies in place.
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