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.

The Doomsday Clock refers to the amount of time humanity has before it effectively kills itself with emerging technologies.

Scientists and global leaders revealed on Tuesday that the "Doomsday Clock" has been reset to the closest humanity has ever come to self-annihilation.