CW-7

Movie and TV series

CW-7 was a cooling agent that was used to cool down the temperatures of the planet in response to climate change.

Jets releasing CW-7 into the upper atmosphere in the opening scene of the movie

 However, CW-7 was too effective and instead froze the planet, starting a new ice age. 

Rockets releasing CW-7 into the upper atmosphere in the TNT series.

Before CW-7 was released, Mr. Wilford knew that CW-7 would freeze the planet, which led to the creation of the Snowpiercer .

Graphic Novels

In the graphic novels though, CW-7 was a climate engineered weapon of mass destruction that was used during a global war over dominance of the planet. It is unknown who activated CW-7.