NEW YORK — In the not-so-distant future, humanity’s last survivors ride a vast, never-stopping train across a frozen Earth. The fictional world of “Snowpiercer,” a new TV series airing on TNT in early 2020, is a grim one. A botched attempt to reverse runaway global warming has left Earth blanketed in ice and snow. Only a few thousand people — some wealthy and privileged and many desperate and wretched — survive, saved by a billionaire’s pet project: a beast of a supertrain (named Snowpiercer) that extends for miles, equipped to ride the rails until Earth is habitable again.

The series is based on the 1982 French graphic novel “Le Transperceneige,” as was the…