LONDON — For the first time on record, Britain suffered under temperatures above 40 degrees Celsius — 104 Fahrenheit — on Tuesday, as a ferocious heat wave moved northwest, leaving a trail of raging wildfires, lost lives and evacuated homes across a Europe frighteningly ill-equipped to cope with the new reality of extreme weather.

While the heat’s effects cascaded from Greece to Scotland, the greatest damage was in fire-ravaged France. More than 2,000 firefighters battled blazes that have burned nearly 80 square miles of parched forest in the Gironde area of the country’s southwest, forcing more than 37,000 people to evacuate in the past week.

Temperatures fell overnight on Monday, but the efforts of the firefighters have been hampered by fierce gusts of wind, arid conditions and scorched trees that sent fiery embers through the air, further spreading the flames.

“Climate conditions are crazy,” said Matthieu Jomain, a spokesman for the regional firefighter unit. “It’s an explosive cocktail.”

Spain, Italy and Greece also endured major wildfires, and in London, a series of grass fires erupted around the capital on Tuesday afternoon, burning several homes — an ominous sign that the destruction could hopscotch the English Channel.

London’s mayor, Sadiq Khan, said the city’s fire brigade was “under immense pressure” and the brigade declared a “major incident,” allowing it to focus its overstretched resources on serious incidents.

The temperature in Paris reached 40.5 degrees Celsius on Tuesday, or 104.9 Fahrenheit. The city had recorded temperatures above 40 only twice before, in 1947 and 2019, according to the national weather forecaster.

Britain never recorded a 100-degree temperature before 2003, and until Tuesday, the record had stood at 38.7 degrees Celsius, or 101.7, set in Cambridge in 2019. The country made a bit of meteorological history before noon, when the thermometer in Charlwood, a village in Surrey north of Gatwick Airport, reached 39.1 Celsius — and then quickly left that new record far behind.

At Heathrow Airport, the mercury hit 40.2, breaking through a barrier that once seemed unimaginable for a temperate, northern island — a record that was surpassed a few hours later when Coningsby, a village in Lincolnshire, reached 40.3 degrees, or 104.5 Fahrenheit.

At least 34 sites broke the old British record on Tuesday, according to the Met Office, the national weather service, including at least six that reached 40 Celsius. Scotland blew by its old record of 32.9, with a reading in Charterhall of 34.8 — 94.6 Fahrenheit.

The heat continued a global pattern in recent years of leaping past records rather than breaking them in tiny increments.

Amid the Guinness Book-style excitement at falling records was a somber recognition of the human cost of dangerous heat waves. The police in London said they had recovered a body from the Thames River and believed it to be that of a 14-year-old boy who went missing while swimming on Monday.

As temperatures soared, fears for residents of nursing homes also rose. Residential nursing homes are not equipped to deal with extreme heat. Many are housed in older or converted buildings, without air-conditioning. This is a particularly fraught issue in Britain, where critics say the government’s inept handling of nursing homes during the coronavirus pandemic caused needless deaths.

Experts and staff members said greater measures must be taken to protect older people. Those over 75 years old — whether living on their own or in a care home — are among the most at risk for severe health complications from the heat, according to the country’s Health Security Agency.

“The last 48 hours have been unprecedented, so that’s a massive concern,” said Helen Wildbore, the director of the Relatives & Residents Association, a national charity for older people in care homes and their relatives. She said that the organization’s help line had been inundated with calls in the last week.

For most people, however, a second day of extraordinary heat mostly meant a second day of disruptions. Some public transportation, many offices and some schools remained shut down. The government urged people to continue to work from home — a call that many heeded again on Tuesday — but for schools to stay open.

Network Rail, which operates the country’s rail system, issued a “do not travel” warning for trains that run through areas covered by a “red” warning issued by the Met Office. The red zone covered an area stretching from London north to Manchester and York. Several train companies canceled all services running north from the capital.

Trains are particularly affected by intense heat because the infrastructure — rails and overhead wires — is not built to cope with triple-digit temperatures. Those still running were subjected to strict speed restrictions. The London Underground, most of which is not air-conditioned, also suspended some of its service.

Britain’s heat created a torrid backdrop for another big day in the intensifying, still-unsettled race to succeed Boris Johnson as Conservative Party leader and prime minister. A fourth round of voting by Conservative lawmakers on Tuesday narrowed the field to three contenders; when only two remain, the winner will be chosen between them by a vote of rank-and-file party members.

Rishi Sunak, the former chancellor of the Exchequer, won 118 votes, putting him on the cusp of advancing to the next stage. Penny Mordaunt, a little-known junior trade minister who has mounted an unexpectedly vigorous campaign, came in second with 92 votes, while Liz Truss, who is serving as foreign secretary, was third with 86 votes.

With no candidate gaining fresh momentum and the three survivors relatively close to each other in votes, analysts said it was impossible to predict which two would emerge from the next round of voting on Wednesday. The new leader and prime minister will be announced after the party vote, in early September.

There was a sense, with the uncertainty and shattered heat records, that Britain’s politics and weather were simultaneously edging into uncharted terrain.

Rarely has a political campaign seemed less tethered to everyday reality. Climate change has barely figured in the debate among the candidates. To the extent it has, the candidates have offered only qualified support for Britain sticking to its goal of reaching “net zero” in greenhouse gas emissions by 2050.

“What it reveals is the gap between politicians and the public,” said Tom Burke, the chairman of E3G, an environmental think tank, and a former government adviser. “The recent sequence of weather events has confirmed the science in the public mind, but politicians, especially on the right, don’t get that.”

Mr. Burke said the Conservative candidates were promising smaller government, lower taxes and fewer regulations. Any effective climate policy, he said, would require tighter regulations, state intervention and some higher taxes.

Britain, of course, is not the only country where climate policy has collided with fears of a cost-of-living squeeze. In Washington, Sen. Joe Manchin, Democrat of West Virginia, cited surging inflation as a key reason he refused to agree with fellow Democrats and the White House on a comprehensive climate package.

“The cost-of-living crisis is really an excuse for inaction,” Mr. Burke said.

Britain may be a microcosm of the climate crisis, but it is being waged in myriad other ways across Europe.

In France, the authorities responded to this week’s dangerous conditions with warnings and contingency plans, hoping to avoid a repeat of the devastating death toll the country suffered in a 2003 heat wave. In August of that year, some 15,000 people died, including many older residents in retirement homes that lacked air-conditioning, shocking the public and fueling anger at a government it considered ill-prepared.

In Greece, thousands of residents were ordered to leave their homes on Tuesday as a wildfire tore through forest land north of Athens. Although temperatures were not unusually high, dry conditions and strong winds stoked dozens of wildfires, the largest in the Mount Penteli area, northeast of Athens.

In the Netherlands, workers sprayed water on mechanical drawbridges over Amsterdam’s canals to prevent the metal in them from expanding, according to The Associated Press. That can jam the bridges shut, blocking marine traffic.

Amid all the sweltering, there was a promise of relief: Forecasters across Europe said the heat would ease its grip by midweek. In Britain, some showers were expected, and temperatures were forecast to plunge, staying below 80 Fahrenheit in most of the country on Wednesday.

Reporting was contributed by Megan Specia and Euan Ward in London, Aurelien Breeden in Paris, Constant Méheut in La Teste-de-Buche, France, and Niki Kitsantonis in Athens.