AUDIE CORNISH, HOST:

The Doomsday Clock is not an alarm clock, but it is meant to be alarming.

ROBERT SIEGEL, HOST:

It's more of a metaphor than an actual clock. The Doomsday Clock was created by the Bulletin of Atomic Scientist's Science and Security Board decades ago. It's a warning about the dangers facing humanity.

CORNISH: And the board announced today that they've moved the clock forward by two minutes. It's now three minutes to midnight. And the reasons why we're closer to doom?

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KENNETTE BENEDICT: Today, unchecked climate change and a nuclear arms race resulting from modernization of huge arsenals pose extraordinary and undeniable threats to the continued existence of humanity.

SIEGEL: That's Kennette Benedict of the Bulletin of Atomic Scientists. This figurative countdown was last reset three years ago. The Doomsday Clock was created in 1947, and it's been adjusted just 18 times.

CORNISH: The nearest it ever was to midnight was in January 1953, a few months after the first test of the hydrogen bomb. Transcript provided by NPR, Copyright NPR.