The heat waves hitting Europe and North America would have been impossible without the climate crisis

2023-07-25 06:55:04
In Beijing, July 11, 2023. ANDY WONG / AP

More than 50°C in the United States and China, nearly 45°C in Italy, Spain and Greece… Many regions of the northern hemisphere have been subjected, since the beginning of July, to extreme and dramatic heat waves.

These disasters are in no way due to chance or natural climate variability: heat waves in Europe and North America would have been impossible without climate change, while that in China has been made at least fifty times more likely due to global warming. While they may still seem exceptional, such events are in fact no longer rare in the current climate and will increase in the future.

These are the conclusions of a study published Tuesday, July 25 by scientists from World Weather Attribution, an international network of researchers specializing in the science of attribution. This discipline consists of characterizing the influence of the climate crisis on the probability and intensity of individual extreme events based on rapid studies, carried out according to a precise protocol reviewed by peers. Scientists used observations and climate models to simulate these heat waves in both the current climate – which has already warmed by 1.2°C – and the pre-industrial one.

Read the summary: Article reserved for our subscribers Climate: hundreds of millions of people affected by extreme temperatures

The analysis focused on the period during which the temperature was the highest and therefore the most dangerous for health in each region: from July 12 to 18 in southern Europe, from July 1 to 18 in the southwestern United States and northern Mexico, and from July 5 to 18 in western and central China.

During these periods, the mercury exceeded 53°C in Death Valley (California) and 52°C in China; Catalonia (Spain) experienced its hottest day on record (over 45°C) while Greece and the city of Phoenix, Arizona (USA) experienced their longest heat wave. More than 100 million Americans have been placed on red alert, more than 200 Mexicans have died from the heat and many deaths or hospitalizations have been recorded in Europe.

Increase in frequency and intensity

“However we characterize these events, in terms of duration and spatial extent, the results are absolutely the same and show the overwhelming role of climate change”, says Friederike Otto, a climatologist at Imperial College London. Conversely, the natural phenomenon El Niño, which began in June, plays only one “very moderate role” ; this warming of part of the equatorial Pacific Ocean generally results in a rise in global temperatures but it only marginally influences heat waves in Europe, China and the southern United States, assures the scientist.

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