The amount of global warming that influenced the UK’s heatwave last week is likely to be underestimated because climate models aren’t doing a good job of reproducing how quickly temperatures in Western Europe have risen.

On 20 July 2022, a wildfire engulfed the Shiregreen neighborhood of Sheffield, England. Getty Images/Christopher Furlong

According to a team of researchers, the unprecedented 40°C heatwaves that hit the UK last week were made at least ten times more likely by climate change. The extreme event would have been about 2°C cooler if not for human-caused global warming.

Even in today’s changing climate, the World Weather Attribution (WWA) team concluded that the provisional 40.3°C records set in Coningsby, Lincolnshire, should only occur in that area once every 1500 years.

“We know it’s still a rare event today,” says Friederike Otto of Imperial College London, who is part of the WWA team. “Without climate change, it would have been an extremely unlikely event.”

Climate change has made most heatwaves more likely and intense, but studies are still needed to determine how much. Without human-caused warming, the team found that the likelihood of such high temperatures occurring in the UK’s normally temperate climate was “extremely low.” Because climate models aren’t doing a good job of reproducing how quickly temperatures have risen in Western Europe, the estimate of at least ten times more likely with human-induced warming is thought to be on the low side. “We don’t know why,” Otto says.

The researchers examined the two hottest days of the year, July 18 and 19, in an area that included east Wales and parts of England, including London. The group then examined the maximum temperature for one day and the average temperature over two days in a world with and without climate change since the industrial revolution.

According to the analysis, the two-day heat that occurred across the entire studied area would occur once every 100 years in today’s warmer world. However, the temperature would have been “nearly impossible” without the 1.2°C of global warming caused by fossil fuel combustion and other human activities since the 19th century.

The heatwave sparked destructive wildfires across the UK, severely disrupted rail transport, forced some schools to close, and 948 people are estimated to have died in England and Wales over three days. A total of 46 weather stations met or broke the UK’s previous temperature record, set in 2019, of 38.7°C. The extreme heat followed the driest January to June in England since 1976, prompting warnings on July 25 that drought could be declared for large parts of the country in August.

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