A sweltering night in Cardiff has broken another new UK heat record as brutally hot conditions continue across England and Wales. Temperatures only fell to 23.5C overnight in the Welsh capital, the Met Office said, making it the highest minimum temperature ever recorded in June.

The UK’s high temperature record for June is also likely to be broken on Thursday, just a day after the previous record. The heatwave, supercharged by the climate crisis, drove the temperature to 36.1C at Gosport in Hampshire on Wednesday, beating the previous record of 35.6C set in Southampton in 1976.

Heatwaves are now more severe and more likely because of the carbon pollution from burning fossil fuels, with scientists estimating the current extreme temperatures across Europe are between 2C and 4C higher as a result.

Many thousands of people are likely to have died prematurely in the heat, but the statistical analysis required to determine the number takes time to complete. The UK Health Security Agency found that more than 10,000 people died in Britain owing to summer heatwaves between 2020 and 2024.

The UKHSA has extended its red heat-health alert by 24 hours to 11pm on Friday. It is only the second red alert ever issued by the agency. The Met Office also extended its red alert for south-east England until 9pm on Friday. Rising global heat is now killing one person a minute around the world, health experts said in October.

“Europe’s savage heatwave is the latest price to pay for fossil fuel pollution baking our planet,” said Simon Stiell, the UN’s climate chief. “Schools closing, the vulnerable dying, economies sweating: this is what the climate crisis looks like in practice, and it’s just getting started.” Global heating will not stop until carbon emissions fall to net zero, but they rose again in 2025.

“Extreme heat will keep getting worse, and other climate impacts – from mega-droughts, floods, wildfires and storms – will keep hammering every economy and population harder each year,” said Stiell. “But the solutions are equally clear: a faster shift to renewables – which are now much cheaper than fossil fuels – as well as protecting forests. There’s no time to lose.”

The UK parliament voted overwhelmingly on Wednesday to set a legally binding target of an 87% cut in emissions by 2040. That figure was proposed by the government’s official adviser, the Climate Change Committee, which said in May that the UK’s infrastructure was “built for a climate that no longer exists” and needed urgent improvement to protect people from the climate crisis.

Many schools have closed and rail journeys have been cancelled during the UK heatwave this week, which has been made even more dangerous and uncomfortable by high humidity.

Sadiq Khan, the mayor of London, launched the city’s first heat plan on Thursday. “Extreme temperatures are no longer a future threat, they are a present danger,” he said. The plan includes retrofitting homes at the highest risk of overheating, more tree cover, and safe access to water for paddling and swimming. A 2025 study found the number of UK homes reporting overheating in summer quadrupled to 80% in a decade.

Measurements taken by Greenpeace found pavements, rail platforms, building sites and other places across London reached surface temperatures of 50C to 60C on Wednesday. The black rubber floor of a playground in Islington was recorded at 53C at 5pm.

“This record-smashing heatwave has turned London into a sticky, sizzling cauldron,” said Mel Evans, Greenpeace UK’s head of climate. “This isn’t just weather – it’s a public health emergency driven by fossil fuel giants. These abnormal temperatures are stretching homes, schools, transport and our own health to breaking point.”