All hail the train!
There's nothing new or interesting about dystopian, apocalyptic futures, be they Snowball Earths or otherwise. Suppressed lower classes rioting against a perverted bourgeoisie that devours what few resources left - dime a dozen. The fascinating, if heightened-suspension-of-disbelief-demanding thing Snowpiercer does to make it fresh is monumentally decreasing the scale of the event. What happens when a civil uprising takes place on a single train holding all of humanity, brought back to perhaps a few hundred?