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.

In an announcement, the Bulletin of the Atomic Scientists moved the Doomsday Clock forward by one second to 89 seconds before midnight, the closest it has ever been to signaling a global catastrophe.

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