Heat wave without climate change “extremely unlikely”

Such records could be repeated every 100 years – at some point every three years

However, the discrepancy between the comparisons in the observations and the simulations forces the research team to be rather cautious about the quantitative result of their analysis. Global warming has made the English heatwave at least tenfold more likely. Analysis of other extreme events provided factors of 30, for example the heatwave in India and Pakistan in March 2022. The heat that hit Canada and the US Pacific Northwest in 2021 was, according to the study, “virtually impossible” without climate change. “The word ‘at least’ in the figures for the British heat wave is therefore particularly important, because it was certainly more than ten times as likely,” emphasizes the researcher from Oxford.

According to Otto, the reason for the discrepancy between the two analysis methods lies in a well-known weakness of the global climate models: they underestimated the trend in regional heat waves in Western Europe, although they otherwise provide good values ​​and correctly depict average temperatures or extreme rainfall, for example. However, the reason for this is still open. “For us in Europe, that means we could get higher temperatures even faster than expected,” says the physicist.

Despite these unsatisfactory details, the new analysis confirms calculations published by the British weather service Met Office 2020. According to the study at the time, temperatures of 40 degrees Celsius or more would have occurred in Great Britain every 1,000 to 10,000 years at best, if the atmosphere were still in the composition it was in before industrialisation. But in today’s climate, which has already warmed by 1.2 degrees, the extreme heat is likely to repeat itself every 100 to 300 years. And if climate change continues unchecked, after 2100 such an extreme summer would be expected every three to four years.

“It’s very sobering that something like this should happen so soon after this study,” says Fraser Lott of the Met Office. “However, our new study confirms the results of the old ones.” Average temperatures, such as those reached over the days of the heat wave on July 18 and 19, 2022 and the night in between, could be repeated every 100 years in today’s climate, the team says calculated around Friederike Otto. The peak values ​​of individual stations, on the other hand, remain less likely and have statistical repetition times of 1000 years. “But we don’t live in a stable climate that has warmed up by 1.2 degrees, it’s changing dynamically,” says Otto. The danger of more frequent temperature extremes is therefore constantly increasing.

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