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 Doomsday clock was set at 89 seconds to midnight on Tuesday morning, putting it the closest the world has ever been to what scientists deem is "global catastrophe." The decades-old international symbol,