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The unprecedented 40°C heatwave that hit the UK last week was made at least 10 times more likely because of climate change, according to a team of researchers who have found that the extreme event would have been about 2°C cooler without human-caused global warming.

The World Weather Attribution (WWA) team, which conducts rapid scientific analyses attributing the influence of climate change on extreme weather incidents, concluded that the provisional 40.3°C record set in Coningsby, Lincolnshire, should only occur in that area once every 1500 years, even in today’s changed climate. 

“We know it’s still a rare event today,” says Friederike Otto at Imperial College London, part of the WWA team, referring to the heatwave broadly. “It would have been an extremely unlikely event without climate change.” 

Most heatwaves have been made more likely and intense by climate change, but studies are still required to quantify by how much. The team found the likelihood of such high temperatures occurring in the UK’s normally temperate climate was “extremely low” without human-caused warming. The estimate of at least 10 times more likely with human-induced warming is thought to be on the low side, because climate models aren’t doing a good job of reproducing how fast temperatures have risen in western Europe. “We don’t know why,” says Otto.

The team looked at the two hottest days, 18 and 19 July, over an area stretching across east Wales and parts of England, including London. The group then modelled a world with and without climate change since the industrial revolution, examining the maximum temperature for one day and the average temperature across two days.

The analysis showed that the two-day heat that occurred across the whole studied area would happen about once every 100 years in today’s warmer world. But the temperature would have been “nearly impossible” without the 1.2°C of global heating since the 19th century because of fossil fuel burning and other human activities. 

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

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