16-07-2025
The London Tube ‘feels like hell.' Efforts to cool it just make it hotter.
A century ago, the London Underground wooed passengers during the summer with the promise it was 'cooler below." That seems like a cruel joke today.
'It genuinely feels like hell down there," said Hussein Zaaiter, a London-based student. 'It's a free sauna on the Central line," he joked, referring to one of the Tube's hottest train lines.
Riding the Tube during the summer has long been an unpleasant, sweaty experience. The bad news for Londoners is that the Tube isn't just hot, it's getting hotter. And figuring out how to cool it down presents challenges that air conditioning can't easily fix.
Engineers have spent decades trying everything from industrial fans to giant blocks of ice to temper the sweltering subterranean climate, but a remedy remains elusive.
Heat has been steadily building below the surface ever since the world's oldest underground transportation system opened in 1863. Across all lines, average temperatures increased by 1 to 3 degrees Celsius over the past 10 years, according to measurements from Transport for London.
Summer temperatures on the Tube now regularly exceed 30 degrees Celsius, or 86 degrees Fahrenheit, the legal limit for transporting cattle, pigs and sheep in the U.K.
The temperature at the surface doesn't really affect the temperature in the tube. Throughout the summer, the tube maintains a fairly constant 86 degrees, while the surface wobbles between lows in the 50s at night and as high as 104 degrees during the day.
The busy Central Line is one of the transit system's deeper lines, where narrow tunnels have made it difficult to add air conditioning to trains.
Zaaiter has ridden the Paris Metro and the New York subway, but 'it's never as bad," he said.
For Verity Walker, a musical-theater actress in London, the heat underground has a habit of sticking with her. 'I'm turning up to auditions, and I'm worried I smell," she said. 'The price should be decreased in the summer because of the conditions."
Climate activists turned the Tube into their personal sauna, riding around the city in their bathrobes and hair towels to raise awareness about the heat.
Experts pin the Tube's hot mess on its tight Victorian-era tunnels, which restrict air circulation, especially on deeper lines. Moreover, London's bedrock is composed of a dense, stiff clay that absorbs and retains warmth.
Every day, friction from accelerating and braking trains generates more heat. Even carelessly discarded newspapers obstruct air vents behind seats and trap hot air in train cars, exacerbating the problem.
In 2003, then-Mayor of London Ken Livingston launched a competition with a £100,000 prize for a tunnel-cooling solution, or about $159,500 at the time. Of the 3,400 entries, many simply suggested riders not wear clothes. Other proposals included handing out Popsicles or putting up pictures of snowmen. No practical designs emerged, and the competition was closed in 2005.
Since then, TfL has spent millions of pounds on initiatives to beat the heat. Early attempts included placing large blocks of ice in refrigeration units under train seats, where the thawing ice would cool air passing over it. Groundwater was also tapped to try to cool the tunnels.
Industrial fans were installed at stations. Even after the TfL discovered they slightly increased temperatures because of the heat generated by the motors, the fans remained. Surveys indicated the fast-flowing air made people feel more comfortable.
'It always perplexed me that boffins could produce mobile phones the size of a credit card yet passengers would emerge dripping with sweat from Tube trains," Boris Johnson said in 2018 during his stint as mayor.
Air conditioning has now been added to roughly 40% of London Underground trains, but it is hard to install on the smaller, deeper Tube lines. It also isn't a panacea. AC simply moves heat from one place to another, so while trains may get cooler, platforms and tunnels get hotter.
Engineering experts have proposed various solutions, all to cool reception. Ideas included regenerative braking, where heat from brakes is recovered to use as energy for trains or stations; improved ventilation systems; energy-efficient construction materials; and smart sensor networks to monitor and regulate temperatures in real time.
Even successful solutions, such as using heat pumps to remove excess heat, have proved tricky to employ across the vast network. One London borough uses the excess heat from the local Tube station to warm nearby homes, but expanding the program faces logistical and funding challenges. A citywide heat network is at least a decade away.
TfL, noting the 'stop-start nature of funding," says it's focused on areas that provide the greatest relief to passengers. Next year, after several delays, it plans to finally introduce the first air-conditioned trains on a deep tunnel Tube line. They will still fit along the Piccadilly line thanks to the AC being placed under the trains, a design that took years to master. TfL said it is also exploring the possibility of cooling panels, subject to funding.
While the heat makes journeys uncomfortable for passengers, it's a prolonged punishment for staff—even with the cooling systems in drivers' cabs.
Tube bosses have been encouraging train drivers to drink more water, but union organizer Finn Brennan says that's an impractical solution. 'With more water, we need the toilet more," he said, adding that drivers are often on a strict schedule with limited breaks. 'This isn't a situation that will get better."
With London enduring repeated summer heat waves, some train workers are planning a 'heat strike" if temperatures rise above 96.8 degrees.
TfL has sought to reassure the public, saying it has 'a comprehensive hot weather plan in place" to get through the summer.
Its enduring advice: 'Please carry water with you."
Write to Anvee Bhutani at
