Who Holds the Thermostat

The least believable thing in Snowpiercer is not the train. It's the chemical.

In the film's backstory, the world's governments, worried about warming, release a compound called CW-7 into the upper atmosphere to cool the planet. It works too well. Seventeen years later, in 2031, the Earth is frozen solid and the last of humanity rides a train that circles it without stopping. The first car belongs to the people who paid. The last belongs to everyone else. Bong Joon-ho's film, his English-language debut, is the story of the people at the back working their way to the front, one locked door at a time.

You can enjoy that as a class parable and most people do. But the parable depends on a prior decision, and the decision is the interesting part: somebody, somewhere, decided to adjust the thermostat for everyone, and nobody who lived under it got a vote.

The art: a revolution you can walk through

Start with the shape, because it is the film's whole idea. A train is a corridor, and a corridor is a plot. Every set piece is a door, and behind every door is a different economy. Bong's production designer, Ondřej Nekvasil, built the tail as a dark, monochrome slum, and pushed the front into increasingly florid comfort. The film was shot mostly on sets at Barrandov Studios in Prague: 26 cars, about 100 metres of train, mounted on a gimbal that rocked them to fake the motion. The shoot took 72 days, on a budget of around $40 million, which made it one of the most expensive Korean productions at the time. You can feel the money is all on screen and the camera has nowhere to hide. It's why the tail feels so claustrophobic, and why a school car or an aquarium car, when it opens, feels like an outrageous luxury.

The cast is wildly mixed, and Bong makes it work. Chris Evans plays Curtis, the reluctant leader, and he is at his best when he's allowed to look haunted. Song Kang-ho, as the security engineer Namgoong Minsoo, is the film's dry, unreliable heart, a man who would open any door for the right drug. Tilda Swinton, as the minister who delivers sermons on keeping your place, is a gift to anyone who likes a villain that is also a joke. Ed Harris, as Wilford, arrives late and talks for a long time.

That last point is the problem. The reveal in the engine room is clever on paper: the revolt was staged, Wilford and the old rebel Gilliam have been using uprisings to thin the tail's numbers, and Curtis has been walking down a path somebody else laid. But the film stops to say so, at length, after two hours of letting its images do the talking. The shoutiest scene is also the least trusting. Add a tone that swings between pulpy brawl and fable, and you have a film that doesn't land every beat. It lands enough. That gap, though, is the one between a good film and a great one.

The film also had a rough ride on the way out. Harvey Weinstein reportedly wanted about 25 minutes cut for the American release. Bong's version eventually went out intact, in a limited run in June 2014 via Radius-TWC, in eight cinemas, before widening to more than 150. It took about $87 million worldwide. A film about someone controlling what the back of the train gets to see had its own fight over who controls the cut.

The prophecy: the dial, the pot and the box

Snowpiercer makes four bets. Most of them are wrong. The one that matters is partly right.

The chemical. CW-7 is a fictional compound, but the idea is a real one: stratospheric aerosol injection, spraying reflective particles into the upper atmosphere to bounce a little sunlight back to space. The physics isn't invented. The 1991 eruption of Mount Pinatubo cooled global temperatures by about 0.5 degrees Celsius for up to three years. In 2021 the US National Academies recommended a funded research programme into solar geoengineering, with rules, a public registry and permits for outdoor experiments, and warned that it could bring "unknown or negative consequences".

What happened next is the strange part. Harvard's SCoPEx, the highest-profile outdoor experiment, was cancelled in March 2024 after a decade of argument and the Saami Council's objections to a planned balloon test in Sweden. Meanwhile, a California start-up called Make Sunsets launched weather balloons carrying sulfur particles from Mexico in 2022 and sold the cooling as a carbon-offset product. Its flights were small, between 10 and 500 grams each, according to one academic account. Mexico announced a ban on solar geoengineering experiments in early 2023. And a venture-backed company, Stardust Solutions, has since been set up to do this for profit. The film imagined states doing it in a panic. The version arriving is a start-up with a balloon, and a government with a ban it can't enforce on its neighbours.

The freeze. Here the film overreaches. Pinatubo-scale cooling lasts a few years and shifts the average by half a degree. Nothing we have read suggests that a deliberate injection could freeze an entire planet, and the film never tries to explain how. The ice age is the premise, not a prediction. It's a metaphor for what happens when a fix is applied from above and no one has to live with the error except the people who weren't asked.

The train. The film's survivors live for seventeen years in a sealed vehicle that feeds, waters and warms everyone on board. The nearest real experiment is Biosphere 2, in Arizona, where eight people were sealed in from 1991 to 1993. Their oxygen fell from 20.9 per cent to about 14.5 per cent, and the farm produced about 83 per cent of their diet. The International Space Station recycles about 98 per cent of its water, which is impressive, and still has to be resupplied. A closed loop for a few thousand people is a much harder problem than a closed loop for a few astronauts.

The bar. The tail eats protein bars made of cockroaches, a detail that's meant to turn your stomach. It's also the thing that came true. The European Union authorised house crickets and yellow mealworms as novel foods in 2022 and 2023, and the UN's food agency has promoted edible insects as a protein source. They are not the food of the poor in Europe. They're a start-up product, in protein powder, at a premium.

The reading

Snowpiercer is better as a machine than as an argument. The machine is a corridor you can walk through, a series of doors that tell you who owns what, and it works because Bong never lets the camera leave the train. The argument, about class and control, is made with a hammer, and then explained.

As prophecy, the film is a shrewd miss. It guessed wrong about the physics and about who would hold the dial. It guessed right that somebody would try, that the people trying would be sure they were saving everyone, and that the question of who gets a say would be answered after the balloon went up and not before.

The film's last image is a polar bear, walking on ice, looking at two children who've survived. It's a hopeful beat, and the hope is on the outside, away from the train, away from the engine, with nobody in charge. That's the point worth keeping. The people who built the ark were never going to be the ones who knew how to leave it.