Extraterrestrials contact humanity but only appear to be friendly: Examples:
"To Serve Man" episode of The Twilight Zone 1962 Human species degenerates through speciation: Examples:
Poul Anderson's "Ghetto," a short story in William F. Nolan's collection A Wilderness of Stars and "The Horn of Time the Hunter," a short story in his collection The Horn of Time Monster disguised as an attractive woman: Shambleau Overpopulation forces humans to live in immense towers or beneath the ground: Examples:
Towers: Mack Reynolds' novel The Towers of Utopia Astronaut trapped in an airlock: Examples
2001: A Space Odyssey 1968 film Post-Apocalyptic Barbarism Examples
nuclear war
A Boy and His Dog 1975 filmThe Book of Eli 2010 film
climate change
Poul Anderson's novel The Winter of the World Planet that appears a Paradise Hides Some Horror Examples
"The Apple " episode of Star Trek: The Original Series Catastrophe Caused by Scientific Blunder Examples
Gerald Hatch's novel The Day the Earth Froze