What is the Doomsday Clock? It's 2025 and scientists have reset the clock closer to midnight and global catastrophe. Here's what it all means.

Artificial intelligence was not listed as a chief concern two years ago, the last time the Bulletin of the Atomic Scientists moved the clock closer to global catastrophe.

The Bulletin of the Atomic Scientists shifted the hands of the symbolic clock to 89 seconds to midnight, citing the threat of climate change, nuclear war and the misuse of artificial intelligence.