London. Much of western Europe baked under a "heat dome" on Wednesday as temperatures climbed toward 40 degrees Celsius (104 Fahrenheit), prompting health warnings across the continent and raising concerns in countries where air conditioning remains uncommon.

France recorded its hottest day on record for the second consecutive day. The Meteo-France weather agency said the country's national thermal indicator — an average of temperatures measured at 30 weather stations — reached a record 30 C (86 F), with temperatures exceeding 40 C in some locations, including Paris.

Meteo-France placed three-quarters of the country under a red alert for extreme heat from Thursday through Friday, affecting tens of millions of people. In Brittany, a region better known for its mild climate, heat-related equipment failures left tens of thousands of households without electricity and unable to use fans or cooling devices.

The United Kingdom also recorded its hottest June day on record, with temperatures reaching 36.1 C (96.9 F) in Gosport, southern England. The Met Office issued a red heat warning covering much of central and southern England as well as Wales.

Authorities across Europe warned residents to take precautions, including avoiding strenuous outdoor activities and exercising caution around rivers and lakes. French officials said around 40 people had drowned over the past week.

UK Braces for Possible 40 C Temperatures
The heat has proven particularly challenging in Britain, where buildings, transport systems and infrastructure were largely designed for cooler weather.

The heat dome — a stationary high-pressure system that traps hot air and humidity — has developed as climate change drives more frequent and intense weather extremes. The United Nations has warned that additional temperature records are likely to be broken over the next five years.

"Heat waves are becoming more frequent, longer and hotter with climate change, as a direct result of the fossil fuels we are releasing as a society," said Hayley Fowler, a professor at Newcastle University's Centre for Climate and Environmental Resilience. "We can expect to cope with more and more of these types of events in the years to come."

More than 1,000 schools in England closed because of the heat, while rail operators canceled services and urged people to avoid unnecessary travel in affected areas.

The current red heat warning is only the second ever issued in the United Kingdom, following the July 2022 heat wave that pushed temperatures above 40 C for the first time.

"Red warnings are reserved for the most severe events," said Mark Sidaway, deputy chief forecaster at the Met Office, adding that the impacts could extend beyond people traditionally considered vulnerable to heat.

The temperatures were so unusual that male journalists in the House of Commons press gallery were permitted to remove their jackets during parliamentary proceedings.

Authorities Seek to Limit Health Risks
More than 100 million people in France, Italy and Spain were placed under heat alerts as temperatures continued to climb.

Several of France's most popular attractions, including the Eiffel Tower and the Louvre Museum, shortened opening hours, while schools and public transportation schedules were disrupted.

"It was unbelievably hot inside, so we wonder if it's going to damage the art in some way," said Anna Forsgren, a Swedish tourist who visited the Louvre before its early closing time.

About 68,000 households in Brittany remained without power after two electrical transformers were damaged following an explosion believed to be linked to the heat.

In Italy, 16 cities, including Rome, Milan, Florence and Turin, were placed under the highest heat alert. Temperatures were expected to reach 41 C in Florence and approach 38 C in Milan.

At the Vatican, pilgrims sought shade under umbrellas in St. Peter's Square during Pope Leo XIV's weekly audience.

"We did not feel any heat at all, only great love for the pope," said Monica Ruiz, a pilgrim from Spain.

Businesses Adapt to Extreme Temperatures
Labor unions urged employers to adopt cooling measures similar to those used during the World Cup currently being held in the United States, Canada and Mexico, including mandatory cooling breaks for outdoor workers.

"Taking a break in high temperatures is a common-sense precaution, but too many employers are refusing to put these and other necessary measures in place," said Esther Lynch, general secretary of the European Trade Union Confederation.

Many businesses have already adjusted working hours. At a major construction site along Paris' ring road, workers now begin their shifts at 6 a.m. and finish by early afternoon to avoid peak temperatures.

"As soon as the sun comes out, workers take regular breaks every hour to cool down," deputy site manager Travis Demarque said.