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.

Humanity is closer to species-threatening disaster than ever before, according to the Bulletin of the Atomic Scientists, who today moved the hand of the "Doomsday Clock" to 89 seconds to midnight. That's the closest the clock has ever been to catastrophe.