London's Tube has been running so long it's literally raising the temperature of the earth around it

Londoners swelter on the Central line during the heat wave of 2003. Image: Getty.

“Why is the tube so hot?” is one of those questions Londoners find themselves asking a lot during the three or four days a year when the city’s weather isn’t completely bloody miserable. But it’s not something to which I’ve ever given much thought. Lot of people, enclosed space – the reasons are obvious, surely?

Except, not every underground railway in the world has this problem. And once upon a time, London didn’t either: when the Bakerloo line first opened, posters suggested it was a good place to keep cool on a hot day, an idea that’s clearly nonsensical in 2017.

And then, from the Twitter feed of occasional CityMetric contributor @LeftOutside earlier*, I learned something genuinely amazing:

My mind, as the kids say, is blown.

And it’s true. In 1900, according to this fascinating article in Rail magazine, the ambient heat of the earth surrounding the tunnels – clay, mostly – was around 14°C. In the height of summer, the tunnels were indeed colder than the air above, so it made sense to travel by tube to cool down.

The problem is – trains full of people tend to give off heat. According to this article from a 2007 edition of Plant Engineering magazine, the vast majority (89 per cent) of that heat comes from the train itself (the friction during braking is the big one), 7 per cent from passengers and 4 per cent from “Tunnel support systems”.

What happens to this heat? On the sub-surface lines – basically, those which share tracks with the Circle – it’s not too big a problem. The tunnels are close to the surface, so often emerge into the light for brief periods (Barbican, South Kensington and Edgware Road are all above ground). They also have plenty of ventilation shafts. The heat has somewhere to go.

The deep tubes, though – the ones which are literally tunnels bored through the ground – are more problematic. Most of them are old, so were built before anyone realised heat would be a problem, and don’t come with enough ventilation shafts to solve it. The air is trapped. And so, the heat is absorbed by the walls, and the earth behind them.

In 1900, as noted above, the average ambient temperature was 14°C. Some 117 years and millions of trains later, it can be anywhere between 20°C and 25°C.


 Let’s just say that again: London has been running tube trains so long that the ground beneath parts of the city is now as much as 10°C hotter than it was in 1900.

One result of this is that the earth has become much less effective at absorbing the excess heat. That means the tunnels themselves have heated up, too. A lot: air inside them can often reach as high as 30°C. You’ve probably noticed this is you’ve been on the tube recently.

For the last decade or so, Transport for London has been looking for solutions to this. Some of them involve increasing the capacity of existing ventilation systems (lack of space above ground means it’s extremely difficult to build new ones). Others involve adding systems which circulate water to cool the air. Yet other options involve things like more efficient braking systems, on the grounds that if you put less heat in, you have less to take out.

Experimental air coolers on the Victoria line. Image: Oxyman/Wikipedia Commons.

It’s clear that there’s no easy solution, however: in 2003, then London mayor Ken Livingstone offered a prize of £100,000 to anyone who could come up with fresh ideas. Nobody could think of anything TfL wasn’t already trying, and the prize went unclaimed.

The upside to this story is that other cities have learned from London’s mistakes, and ensured that ventilation systems are an integral part of new metro systems.

The downside is you’re likely to boil every time you get the Central line in summer for the foreseeable future.

*LeftOutside has since been in touch to tell me he was summarising another article, from the Ian Visits blog. I haven’t read that one – the above article is drawn from the two articles I reference, plus some bits from TfL. But in the name of politeness and an easy life I'm acknowledging its existence and adding a link. Read that too, if you like. 

Jonn Elledge is the editor of CityMetric. He is on Twitter as @jonnelledge and also has a Facebook page now for some reason. 

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What it's been like living in one of the few places that never locked down

People enjoy sunny weather in Tantolunden park in Stockholm on May 30, 2020, amid the novel coronavirus pandemic. (Henrik Montgomery/TT News Agency/AFP via Getty Images)

While most of the Western world was confined to their homes for the better part of two months this spring, my friends and I in Stockholm continued hanging out. In stark contrast to most other places, we went to restaurants (occasionally, outside when possible), to one another’s houses (in our yards when possible), and even sent our kids to school. As the rest of the world opens up again, not much will change in Stockholm.

As an American expat living in the Swedish capital, I was initially angry at Sweden’s response to the Covid-19 pandemic. In my home country, early outbreaks in locations such as Seattle, New York City and the San Francisco Bay Area led to strict rules that were soon mirrored in many other states and cities. The Swedish strategy, meanwhile, boiled down mostly to recommendations: If possible, work from home; avoid unnecessary travel within the country; engage in social distancing; and if you’re above 70, stay home. I felt that, in the face of a global pandemic, a country known for its generous welfare policies – that took such good care of its citizens – wasn’t doing its part to protect us.

My friends and I are mostly expats with young families who, early on, pulled our children out of school against official policy. (Schools here only closed for those 16 and over.) We eagerly waited to hear what further action our current country would take. Surely a country known for its progressive social policies would take fast, decisive action to protect its citizens?

The regulations that were put into place in Sweden amounted to restricting public gatherings to no more than 50 people (reduced from 500, which concert halls skirted by restricting entry to 499), limiting restaurants to table service only, and no visiting retirement homes. People here did take the work-from-home guidelines to heart – no one I knew was going in to work. But bars and restaurants were full. My Instagram feed was a highlight reel of acquaintances clinking champagne flutes at the city’s major clubs and restaurants.

After the first few weeks, I slowly started meeting up with friends again. I sent my kids back to school, where they intentionally spent most of the day outdoors and drop-offs were restricted to outside only (parents weren’t allowed to enter the building). I was careful to take precautions like bringing hand sanitizer to playgrounds and wiping my hands after opening and closing the gate to school. Hardly anyone wore masks to the grocery shop or inside stores – the few times I’ve seen people wearing them I’ve done a double take. One busy Friday night in late April at the local supermarket there was a line out the door and someone regulating the number of customers allowed inside at the same time. I took a photo and sent it to my family in the US saying “Sweden finally catching up with the rest of the world!” (I haven’t seen entry to that store being regulated since.)

When I spoke to Swedish friends about the strategy many agreed with the relaxed approach, mentioning that other countries’ draconian measures would be unnecessary in Sweden. A recent poll showed that just 11% of people in Sweden felt they did not trust state epidemiologist Anders Tegnell, who is leading the strategy. In this country, the onus was placed on citizens themselves to follow recommendations. It's about personal judgement and individual responsibility within a framework that rested on mutual trust, rather than top-down control. Swedes’ high level of interpersonal trust and trust in authority was often cited in the press as the characteristic enabling the relaxed Swedish strategy in tackling the virus, as opposed to social distancing becoming a matter of surveillance and policing like in Spain or Italy, where any nonessential socializing was forbidden.

In early May, Sweden's ambassador to the US Karin Ulrika Olofsdotter said in an interview with the Washington Post that some media outlets made it look “like everyone in Sweden is out drinking and partying,” she said. “That is not the case.” But that was certainly how it felt to me. According to research by Esteban Ortiz-Ospina and Max Roser in 2016, in countries such as Norway, Sweden and Finland, more than 60% of respondents in the World Value Survey think that people can be trusted. And in the other extreme, in countries such as Colombia, Brazil, Ecuador and Peru, less than 10% think that this is the case.


Of course, many places in the US also took a similarly relaxed approach to tackling the pandemic, with conservative lawmakers and anti-lockdown activists citing Sweden as taking the right approach. Sweden, rarely finding cheerleaders among conservative US circles, suddenly stood as an example to follow. But since then, places such as Arizona, Texas and Florida have all seen significant spikes in cases following reopenings and are being deemed the new epicentres of the virus – while Sweden’s numbers have stabilised. According to some reports, the death toll in Sweden is one of the highest in the world per capita, but the total number of Swedish deaths remains at just above 5,000, compared to over 120,000 in the US, over 43,000 in the UK, over 28,000 in Spain and over 34,000 in Italy. The mortality rate in Sweden and the number of new intensive care cases in the country declined in the last week and contagion rates here are now “stable” according to the WHO.

Although it didn’t always feel like it at the time, Sweden issued clear guidance from the beginning, with the expectation that people would choose to follow it. It certainly was my experience that everyone I knew stopped going into the office and started working from home. William Hanage, an associate professor of epidemiology at Harvard’s School of Public Health, attributed Sweden’s slowing of the virus to implementing guidance early on. “Sweden’s policy is unusual in that it took a much less stringent approach to preventing transmission," he says, "but interestingly it implemented those measures at a very early stage in the pandemic, before large amounts of community spread had occurred.”

Now I go outside and all too often realise I’ve left my hand sanitiser at home. I even met a friend for lunch outdoors at a busy cafe one particularly sunny day, and another indoors one Friday night for dinner. In May I had a birthday bash in my garden with a dozen or so friends and we ended up at the local bar. I always felt guilty after, as if I’d done something wrong that I couldn’t tell my family in Baltimore about. When I watched international news or spoke to family back home I would feel a certain cognitive dissonance between my own seemingly low-risk reality and what I knew to be happening in the rest of the world. My family in the US calls me skeptically questioning why I’ve had people over in my garden, or been out to eat. I can’t explain the lack of logic that permits an entire city’s citizens to operate life as normal in the midst of a global pandemic. But Stockholm has become a bubble of exactly this.

Being relatively young and healthy, I’m not so worried about getting sick. Even though young and healthy people have gotten seriously ill, there haven’t been any reported cases at my kids’ or any of my friends’ kids’ schools. Nobody I know in Stockholm knows has gotten sick, allowing me to feel a certain distance from it. But my husband’s parents are in their mid-70s and weren’t able to see their grandchildren for two months save for a few visits to their hallway, where we wave and blow kisses to them standing at the door.

I’ve been grateful – but also felt a sense of guilt for – my freedom here. When there are no hard and fast rules about how to act, it’s easy to constantly question yourself: Is it really okay to be outside, sitting at this full cafe? Is it okay to invite a few friends over for a birthday? Is it okay to send my kids to school? These questions have surely gone through minds around the world in the past several weeks, and now it’s clear that that behaviour had dire consequences in some cities and not others.

While Swedish social media at times suggests an endless friend-filled party at summer homes and popular hangouts, the reality here is a balancing act between personal judgement and the freedom to continue life as normal. Self-regulation is what it comes down to in Sweden, anyway.

Elysha Krupp is a writer and editor currently living in Stockholm.