The heat wave, a marker of global warming

Globally, 2015 to 2022 were the hottest years on record. And punctual heat waves are multiplying all over the globe, with their procession of disastrous consequences, droughts, fires, and of course loss of human life.

The responsibility of human beings

“Every heat wave we experience has been made warmer and more frequent due to human-caused climate change,” summarizes Friederike Otto, of the Grantham Institute at Imperial College London.

“It’s pure physics: we know how greenhouse gas molecules behave, we know that there are more of them in the atmosphere, that the atmosphere is warming, which means that we expect to see more frequent and hotter heat waves and less frequent and milder cold spells.”explains during an online briefing this specialist in the “attribution” of extreme events to climate change.

This growing branch of climate science has calculated that the heat wave of unprecedented intensity and precocity that hit India and Pakistan in March-April was made 30 times more likely by the change climatic.

Or that the extraordinary heat wave in Canada in June 2021, which killed more than 500 people in temperatures approaching 50°C, would have been “almost impossible” without climate change. Or that the warming had added up to 3°C to the very strong summer heat wave in Europe in 2019.

“The increase in frequency, duration and intensity of these (heat waves) events in recent decades is clearly linked to the observed global warming and can be attributed to human activity”abounded on Monday the World Weather Organization, in a commentary on the extreme heat in Western Europe.

The worse is yet to come

And it’s not over. According to UN climate experts, extreme heat waves would be 4.1 times more likely to occur at +1.5°C of average global warming compared to the pre-industrial era, the most ambitious objective of the 2015 Paris Agreement.

It would be 5.6 times more likely at +2°C and 9.4 times more at +4°C. For even more intense and rare heat peaks, the figures increase to 8.6 times more at +1.5°C, 13.9 times at +2°C and… 39.2 times at +4° VS !

However, the planet has warmed by around 1.2°C since the industrial revolution and, according to the UN, the current commitments of States, if they were respected, would lead to global warming. “catastrophic” +2.7°C.

The climate cycle is already profoundly modified, as Matthieu Sorel, climatologist at Météo-France, points out, who notes that the heat waves which are increasing in the country – already two this year – would be 1.5°C less intense. at 3°C ​​without the effect of climate change. “We are heading towards increasingly hot summers, where 35°C is becoming the norm and 40°C will be regularly reached”.

Important consequences

Humans will be increasingly affected by this heat, which can be fatal: 14% of humans would be exposed to the consequences of global warming at least once every five years at +1.5°C but 37% at +2°C , according to the IPCC.

Gold, “everywhere in the world where we have data, there is an increased risk of mortality when we are exposed to high temperatures. (…) And the more extreme these temperatures become, the higher the risk”warns Eunice Lo, of the Cabot Institute for the Environment at the University of Bristol.

And “It’s not just vulnerable people who risk health impacts, even fit and healthy people become at risk”underlines the specialist.

Until you can die, especially from the effect of “wet thermometer”when the humidity contained in the hot air prevents the body from sweating and therefore from evacuating its own heat.

The effects are also devastating for the environment, heat waves reinforcing droughts, favorable ground for fires, such as those which are currently ravaging France, Portugal, Spain, Greece or Morocco.

They can also threaten human food. Hit by the heat wave, India, the world’s second largest producer of wheat, has imposed a temporary embargo on the export of this cereal, reinforcing the crisis triggered by the Russian invasion of Ukraine.