What is the 'Doomsday Clock' and what happens when it hits midnight?

The Doomsday Clock is now at 90 seconds to midnight — the closest we have ever been to global catastrophe

What is the Doomsday clock? Why did it move closer to global catastrophe? What it means

Doomsday Clock: Todos los cómics que debes leer antes de la secuela de Watchmen

The Doomsday Clock, explained

The Doomsday Clock And Climate Change: What It Means For Humanity

Doomsday Clock moves closer to midnight than any point since 1947

Doomsday Clock - Bulletin of the Atomic Scientists