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, which has been used to examine the world’s vulnerability to global catastrophe for nearly a century, has moved one second closer to midnight. On Jan. 28, the Bulletin of the Atomic Scientists announced that the Doomsday Clock was set at 89 seconds to midnight,

The Bulletin of Atomic Scientists announced Tuesday that the "Doomsday Clock" is now set to 89 seconds to midnight.