Exceptionally early heat wave shatters records and brings deaths in Europe

London also recorded a rare "tropical night," defined as one in which the temperature does not fall below 20 C (68 F).

Records also fell in France, where temperatures reached 36 C (97 F) on Monday in the country's southwest and widely remained above 20 C at night.

The national weather service, Météo-France, said a "heat dome," with heat held in place by a high-pressure weather front, was producing temperatures more than 10 degrees Celsius above what is usual for this time of year.

Unpredictable and extreme weather is becoming more frequent as Earth warms. Experts say unprecedented and deadly weather extremes that sometimes strike at abnormal times and in unusual places are putting more people in danger.

"We know beyond a shadow of a doubt that heat wave events such as this have been made more likely and more severe due to climate change arising from our emissions of heat-trapping greenhouse gases," said Peter Thorne, director of the ICARUS Climate Research Centre, at Maynooth University, in Ireland. "But, nevertheless, many of the records being set, particularly in the U.K. and France, are mind-bogglingly crazy."

After a U.K. long weekend that sent people flocking to beaches, pools and shady parks, London commuters sweltered on Tuesday in subway carriages without air conditioning. Trains to and from the busy Waterloo station were disrupted by a report of smoke on the tracks.

In Scotland, firefighters worked through the night to douse a grass fire that sent smoke billowing from Arthur's Seat, the rocky hill that looms over Edinburgh.

The U.K. Health Security Agency issued an amber health alert for large parts of the country through Thursday, warning of a potential health risk, particularly among older people, at the hottest times of the day. The U.K. is used to moderate temperatures, and many homes, schools and businesses do not have air conditioning.

At least four teenagers died in apparent drownings in U.K. lakes and reservoirs, and a 60-year-old man died in the sea in southwest England, authorities said.

French government spokesperson Maud Bregeon said there have been reports of at least seven deaths potentially related to high temperatures, including five drownings and two deaths in sports competitions.

The early heat wave has struck before the annual summer window when lifeguards watch over bathers at popular beaches, increasing risks.

On France's Atlantic seaboard, where magnificent beaches have powerful riptides, officials reported a rash of emergencies in the surf, with two drowning deaths on Sunday at popular resorts in the Gironde region in the southwest.

The top regional administrator, Sophie Brocas, urged beachgoers "to exercise the utmost caution."

The unseasonable heat extended to Spain, where weather service spokesperson Rubén del Campo said: "We find ourselves with temperatures we normally see in the middle of the summer now in the month of May."

He said Seville hit 38 C (100 F) over the weekend, while large parts of the Iberian Peninsula saw temperatures 5 to 10 degrees Celsius higher than normal.

And in Rome, temperatures were expected to reach 32 degrees C (89.6 F) on Tuesday.