The Doomsday Clock now stands at 89 seconds to midnight, the closest to catastrophe in its nearly eight-decade history. Here's a look at how — and why — it's moved.

Humans may be one step closer to destroying the world, or at least that's what scientists behind the Doomsday Clock think. The Bulletin of the Atomic Scientists is a nonprofit organization dedicated to tracking human-made threats to the environment.

A science-oriented advocacy group advanced its famous clock to 89 seconds Tuesday, the closest it has ever been.