The Freeze

The Freeze is a human-engineered catastrophic event that started seven years ago before, during and after the boarding of Snowpiercer.

History

The Earth's temperature is rapidly rising due to climate change causing the global warming effect. Wars also made the earth even hotter. The Freeze is the consequence of using CW-7 to lower the Earth's temperature, as using the chemical had a much harsher result than expected. CW-7 caused a massive drop in temperature, peaking at about -120°C.^[1]
The resulting climate change killed off almost all life on Earth, leaving Big Alice and Snowpiercer carrying the only known survivors^[1].
Before Snowpiercer's Departure it was -40 degrees in June, according to Zarah, and dropping. At departure it was -45 degrees and getting colder by the minute.^[2]
It is revealed that the rich who doesn't get to board the trains tried to hole up in bunkers or upload their consciousness.^[3]
According to newspapers in the Library Car, medics and scientists predicted that the population would survive unless the weather changed, which it did. It also stated that million of people are migrating to warmer countries in the equatorial, making the countries closes their boarder. Other newspaper stated that first class vegetable are gone and how Nuclear Plants attracted a lot of survivors, which could be a good explanation of how Asha survived.^[4]

Pre Series

In the first year Joseph Wilford separated 3 cars from Big Alice to save weight and resources, leaving 100 people to die in their sleep, on a secondary track.^[5]^[6]
After the failure of the Year Three Rebellion, 13 people including Old Ivan had an arm frozen off.^[1]

Throughout the Series

Season 1

It is revealed that the temperature outside of Snowpiercer during its passing of Yukon, Canada is around -120°C.^[1]
After the failed revolution Ruth Wardell freezes an arm off of Suzanne, who volunteered to save her daughter Winnie.^[7]
While traveling through Yukon, a Class 3 avalanche breaks a window to the Cattle Car, killing all of the cows and workers, leaving bovines extinct.^[7]
After realizing Andre Layton escaped from The Drawers, Melanie Cavill tortured Josie Wellstead in The Hospitality Car by using a hose connected to the outside and shattered one of her fingers. Later, with help from Bess Till, Josie freezes the rest of her hand to escape and attempts to kill Melanie by flooding the room with the Freeze. Instead, Melanie escapes, leaving Josie to die in the room filled with outside air.^[8]
During the Revolution, the Jackboots executed prisoners, such as Walter Flemming, by Lung of Ice.^[9]
At the end of the Revolution, 7 cars were separated from the train and sent onto a siding.^[9] The occupants froze to death in 13 minutes.

Season 2

After suffering a suit breach, causing frostbite to her shoulder and lungs, Melanie discovers snow falling despite the fact that it is supposedly too cold for snow, suggesting that the planet is beginning to recover from the Freeze and coming again.^[10] After further study, with a Weather balloon, Melanie determines that CW-7 is actually breaking up in the upper atmosphere and falling to the Earth, meaning that the planet will potentially be suitable for colonization again in the survivors' lifetime rather than in a thousand years.^[11]
Wilford brought Snowpiercer to a stop twice, in a attempt to freeze everyone to death, but is foiled both times by Melanie.^[10]
During the failed invasion of Big Alice, Icy Bob activated a Freeze deployment system in the Docking Car, that released Freeze air, that injured and killed the invaders and forced them to retreat.^[10] Icy Bob also exposes himself to the Freeze, in a sub-zero chamber, in the lab on Big Alice.^[12]
After blowing up the Connecting Mechanism, Wilford told Melanie: "My crew know life below zero. We’ve run a lot of rough miles together."^[11]
After being discovered as Wilford's informant, Pastor Logan commits suicide by breathing in the Freeze, with a hose and bag on his head.^[13]
Boki lays the Breachmen to rest by dumping the bodies out of a car while passing over a bridge. The bodies then shatter upon impacting the frozen surface.^[14]
After the Breachmen murders, rioters (including Jakes Carter) attempted to Freeze off an arm of Pike and then Layton, before being stopped by Ruth.^[15]
Icy Bob later walks along the top of the trains to sabotage The Engine and afterwards dies aboard Big Alice.^[14]
Josie exposed her hand to the Freeze in a chamber designed to open to the outside and discovered she has resistance to the cold.^[16]
After taking control of the train, Wilford executed the 8 Breachmen murderers (including Eugenia) in a car by the Lung of Ice.^[16]
After Wilford sabotaged her rescue, Melanie returned to the Breslauer Weather Station. Realizing she would not survive, she used the last of her power to save the data, wrote a note to Alex, put on her EVA Suit and walked outside to die.^[17]
Wilford attempted to have Josie kill Bennett Knox (and Sykes) by breaching The Engine.^[17]
When Josie breached The Aquarium to create the Pirate train, the cold caused the water to freeze, killed all aquatic life and expanded, destroying the Car and injuring Boki and killing some Jackboots.^[17]
After being recovered by Layton and Alex, Melanie's data shows several areas that are warming, in most of Central America and South Mexico, parts of the top and bottom of South America, Spain and southwest Europe, much of the upper parts of Africa as well as the Middle East and Greece, parts of Asia, South Africa and Madagascar, about two-thirds of South Australia and two small spots in the Dominican Republic and South India. However, North America still appears to be completely frozen over with no warm areas.^[17]

Season 3

Without Snowpiercer’s engine, temperature inside Wilford's Rolling Gulag is in the negatives. First Class is decommissioned, with temperatures in the 1st Class Dining car reaching -25°C. Deaths also occurred from influenza.^[18]
Research reveals that the Philippines and the Horn of Africa are warming, while the upper parts of Africa and parts of the Arabian Peninsula are no longer warm.^[18]
While returning to the Pirate train, after collecting the ice cores, Bennett falls through the roof of a bunker and almost freezes to death, when his suit nearly runs out of power. Layton and Josie rescue him, though Layton himself almost freezes to death after giving Ben enough battery to last until getting on the train. While investigating sounds, Layton finds a survivor.^[18]
Later Bennett determines that the locations checked out won’t be habitable for about a century, as even though it’s warming, the trends aren't steep enough to be habitable yet. However the Gulf of Aden has yet to be investigated.^[19]
Kevin McMahon used a hose filled with the Freeze in the Night Car to torture Strong Boy to death.^[20]
After failing to escape the rail yard and the Pirate train, Wilford threatened to kill everyone on the train (including himself), unless the Pirate train reconnected.^[20]
After taking the train, Layton tells Snowpiercer that they have visited Sulawesi (Indonesian Island), Gujarat (India), Managua (Nicaragua), the Atacama (Chile) and that not one of them was warm enough for life.^[20]
Big Alice later arrived at the warm spot, a microclimate (inversion), in a valley, in the Horn of Africa and found the temperature to be above freezing, with a lake of liquid water and melting snow.^[21]

Trivia

The mean annual temperature of the interior of Antarctica is -57°C, making the world in the Freeze almost three times colder.
As mentioned by Alex, nematodes (roundworms) will survive.^[11]
After the Freeze killed all life on Earth, the only animals left are on Snowpiercer and Big Alice. They include, a pet tegu (in First Class), Erik Sotto's cat (Snowpeter), aquatic life in the Aquaculture Cars, fish in a tank (in Jinju Seong's quarters), pigs, goats, poultry, sheep, rats with the Tailies or the Headwoods' Lab, 2 or 3 dogs (including Jupiter) and cockroaches.
Bees^[3] and cows^[7] survived on Snowpiercer for 4 and 7 years, before they went extinct.
CW-7 was originally engineered to last a thousand years, in order to protect the Earth from Global Warming for that long.^[11]
According to the first weather balloon launched from the Engine, the temperature in the upper atmosphere is at least -86 degrees Celsius (presumably -26 degrees or more, due to beeping heard from the computer every time the readout got warmer).^[11]
In reality, creating a thing like CW-7 would be Stratospheric aerosol injection.