Global warming responsible for earlier and earlier heat waves

Heat waves have become common, but this one is surprising. The planet is warming and the consequences are being felt earlier and earlier. Having just arrived from Spain, a heat wave set in on Wednesday June 15 in France with temperatures expected to exceed 30°C in most regions. The mercury should panic again by crossing the threshold of 40 ° C on Friday.

In France, forecasters and meteorologists describe this episode as “remarkably early”. Until now, the heat wave episodes occurred in August or July. This precocity is unprecedented. It is worrying, and it has been proven: the global warming related to human activities bears the responsibility.

“With climate change, these events happen earlier and last until later in the year, they are also more intense than they could have been in the past”, explains Aglaé Jezequel, climatologist. “Today is the exception, but the climate is changing and we can already expect the heat waves to arrive earlier.”

A taste of our future climate

Will the extreme gradually become the norm? Yes, if we remain passive in the face of climate change, say the scientists. “The consequences of heat wave and the increase in heat waves, we are already experiencing them today, but it can become much worse in the future if we continue to emit greenhouse gases (GHGs)”, continues Aglae Jezequel.

Oil, gas, coal. Pointed out for a long time, they are the main responsible for global warming. On December 12, 2015, meeting at the COP21world leaders embraced the historic Paris Agreement, setting out long-term goals to guide all nations. Among these commitments on the climate, that of considerably reducing global GHG emissions with the aim of limiting global warming to 2°C during the present century, while pursuing the action taken to limit it even further to 1.5 °C.

Last September, two months before Glasgow COP 26sorry for a goal very far from being achieved, the Secretary General of the UN, Antonio Guterres, warned: “The world is on a catastrophic path towards +2.7°C of warming”.

>> To read also: COP26: coal, “losses and damage”, deforestation… What does the Glasgow Pact contain?

The multiplication and intensification of heat waves around the world are the most obvious manifestations of global warming caused by GHG emissions. “We are living a taste of our future climate and so that this taste does not become the norm, there is only one solution: to reduce GHG emissions due to the combustion of fossil fuels”, insists Christophe Cassou, climatologist, at the microphone of France Inter.

According to the CNRS research director, also co-author of the 6^e report of the IPCC (Intergovernmental Panel on Climate Change), this reduction must be immediate, sustained over time and on a large scale. “It’s not in three years, it’s now, because it’s the accumulation of CO2 emissions that counts for the level of warming, for the level of risk, and for the level of occurrence of these heat waves. “

Heatwaves also more frequent and longer

Meteo France defines the heat wave such as a continuous increase in temperatures for at least three days. This happens when the national thermal indicator (average of the daily temperatures of thirty metropolitan stations representative of the French climate) remains at least three days above 23.4°C, and reaches 25.3°C at least once.

In France, the data clearly show the multiplication of these heat waves. Of the 43 phenomena detected since 1947, nine took place before 1989, the rest between 1989 and 2020: i.e. “three times more heat waves in the last 30 years than during the previous 42 years”, underlines Météo-France.

“The degree of warming of the country compared to the beginning of the XX^e is 2°C, therefore higher than the global average (1.1°C)”, says Françoise Vimeux, climatologist, on France 24. The episode of heat in June comes after a particularly hot and dry spring which has already caused, over a large part of France, a drought of the soil, raising fears for crops and creating favorable conditions for fires. “The month of May was the hottest on record since we have weather records,” adds the expert.

And that’s just the beginning. “Today, the probability of having a heat wave is one chance in ten; in 2030, it will be a chance in 5; and around 2050-2060, it will be a chance in two”, specifies Christophe Cassou. .

More frequent, but also longer heat waves. At our current rate, Météo France forecasts predict an average of 20 to 35 days of heat wave per year at the end of the 21st century.^e century (against 3-4 days at the end of the XX^e century).

However, the duration of heat waves depends on the impacts, says Christophe Cassou. “What we show in the IPCC report is that these heat waves extend longer over the seasons, the summer seasons are longer and will have greater impacts – including heat waves that start early – insofar as they induce risks on agricultural yields”.

But the economic cost of heat waves is even more global. As far as health impacts in France are concerned, they represent according to Public Health France between 24 and 37 billion euros between 2015 and 2020.