The United Nations weather agency warned on Thursday that climate disasters are becoming more destructive as Europe experiences a record-breaking heatwave, with temperatures topping 43°C in western France.

Millions of people across Spain, France, the United Kingdom, Germany, and Switzerland are struggling to cope with the heatwave, which the UN says has also affected agriculture, livelihood, ecosystems, and infrastructure.

The UN said in a statement that France recorded its hottest day on June 24, with a temperature of 30.0°C, surpassing records set in July 2019 and August 2003. Temperatures hit 43.8°C in Pulluau, with French authorities issuing top-level alerts and warning of increased risk of forest fires

At least 40 people died while swimming in France as a result of the heatwave, an incident the World Meteorological Organisation said highlights the dangers of extreme heat.

The WMO noted that temperatures rose above 40°C in Spain between Monday and Tuesday, marking the hottest days in June.

In the UK, authorities issued extreme heat warnings for Gosport in southern England after a daily record high of 36.1 °C was set. German and Swiss authorities also issued red alerts in three cities, respectively.

The WMO and the World Health Organisation said some parts of Europe are likely to experience “tropical nights”, a situation in which temperatures at night do not fall below 20°C. The organisations said this condition increases the risks of forest fires and thunderstorms in some areas.

According to the WHO, heatwaves are the leading cause of weather-related deaths, with nearly 489,000 heat-related deaths recorded annually between 2000 and 2019.

The “savage heatwave has the fingerprints of the climate crisis all over it,” said UN climate chief Simon Stiell, warning that “until humanity stops burning coal, oil, and gas, extreme heat will keep getting worse”.

Mr Stiell underscored the need to end dependence on fossil fuels, shift to renewable energy, and build greater climate resilience.

A regional climate centre under the WMO network predicted that the heatwave is expected to spread across large parts of western, central and southern Europe over the next two weeks.

“The forecast indicates temperatures between 3°C and 10°C above the weekly average for this time of year, while daily maximum temperatures above 35°C are expected in many areas, with some locations in the southwest exceeding 40°C,” the UN statement said.

Armel Castellan, an extreme heat services technical advisor at the climate and health joint office of WMO and WHO, warned that nighttime heat can be deadly because it prevents the body from recovering.

“A day that reaches 38°C but drops to 18°C overnight is very different from a day that reaches 36°C and stays above 25°C through the night. The second scenario carries a much higher health risk,” Ms Castellan said.

“We have just lived through the eleven hottest years ever recorded,” UN secretary-general António Guterres said at a London Climate Action Week on Monday. “Around the world, climate disasters are becoming more frequent, more destructive, and more costly.”  

Mr Guterres warned that the most vulnerable people are the worst hit as El Niño risks “turning up the heat”, resulting in disruptions to food and water systems.