3. Children of Men
Alfonso Cuaron's incredibly dystopic sci-fi masterpiece Children of Men serves up a very unconventional end of the world concept, that with men and women losing the ability to pro-create, the human race will begin edging its way towards extinction. This is a rare film on this list that actually seems pretty plausible; it's entirely possible that our environment could render us sterile, meaning that the sight of a young person would slowly become a thing of a past, and when they die, we'd mourn it, just as in this film. Though Children of Men does have a hopeful message and seeming redemption at its close, its depiction of people at rock bottom combined with a troubling military presence makes for a scary, exhilarating end of the world possibility.
What it tells us: young or old, we're all screwed when Mother Nature turns on us.