Climate change is “unequivocally” responsible for the intensity of the heatwave hitting Western Europe, which would have been virtually impossible 50 years ago, the World Weather Attribution (WWA) group of scientists concluded in a study on Friday.
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Very high temperatures during the day, but also at night, would have been “practically impossible” at this time of year in 1976 – a year also marked by an exceptional heatwave -, conclude these researchers, who are studying the responsibility of climate disruption of human origin in extreme weather events.
A similar heatwave occurring then would have been 3.5°C cooler during the day, and 2.4°C cooler at night, they calculated.
“We concluded that over the last 50 years, during which the planet has warmed by 1.1°C, the probability of a heatwave like this has changed immensely,” said Theodore Keeping of Imperial College London, one of the authors.
“This episode would not have been possible in June without climate change,” he said even more directly during a presentation to the press.
Western Europe has been experiencing extreme temperatures for more than a week, a consequence of the presence above Western Europe of an immense mass of hot air coming from Africa and compressed by high pressures at altitude.
“The climate phenomenon is not particularly unusual, but the temperatures are, or at least were before human-caused climate change,” commented Friederike Otto of Imperial College London.
“Unpleasant and dangerous”
This human-caused climate change results from the massive use of fossil fuels – coal, oil and fossil gas – as well as, to a lesser extent, deforestation.
For their study, scientists based in several European countries compared current weather observation data – but also forecasts for the coming days, since the episode is still ongoing – with observation data from 2003 and 1976.
This work, published very quickly, was not reviewed by other external researchers as is normally the case for scientific publications. But the methodology used has already been validated by the scientific community, emphasize the authors.
In terms of probabilities, hot nights have been made about 100 times more likely today than during the historic heatwave of 2003. Daytime heat spikes have become about 10 times more likely, the researchers calculated.
They also ruled out any responsibility for the natural El Niño phenomenon, which warms surface temperatures in the central and eastern equatorial Pacific, leading to episodes of droughts, floods and record temperatures around the world. It played “no role” in the heat wave.
“Heat stress”, which includes high temperatures and humidity levels, also makes this heatwave “particularly unpleasant and dangerous”, notes Friederike Otto.
According to the study, almost 45% of the 854 cities analyzed in 30 European countries have already broken, or are on the verge of breaking, their historical record for heat stress.
This conclusion refers to a temperature index (called “wet bulb bulb” or WBGT) which takes into account temperature, but also humidity, sunshine or cloud cover. It is particularly widely used in the sporting world.
