People around the world have seen Russia's invasion of Ukraine raise fears of a nuclear war. They have witnessed the coronavirus pandemic take the lives of millions, and they have watched floods and wildfires destroy entire communities. Now, scientists tracking such challenges say humanity is facing "unprecedented danger."

Members of the nonprofit group Bulletin of the Atomic Scientists unveiled an update to their so-called Doomsday Clock in Washington on Tuesday. They use the clock to show how close the world is to ultimate catastrophe.

This was the first change they made to it since 2020. They moved the clock forward 10 seconds, to 90 seconds before midnight -- the latest it has ever been.

The group's president and CEO, Rachel Bronson, said, "Russia's thinly veiled threats to use nuclear weapons remind the world that escalation of conflict by accident, intention or miscalculation is a terrible risk."

Scientists created the clock in 1947 to represent nuclear dangers at the dawn of the Cold War. They have taken into account the risks of bioweapons, climate change and disinformation.

Pointing to the fighting around the Zaporizhzhia nuclear complex, they say the war in Ukraine has revived their initial fears. And, they warn, things could "spin out of anyone's control."

The scientists say China's expansion of its nuclear capabilities is "particularly troubling." They cite officials at the Pentagon who claim the Chinese arsenal could soon rival that of the US and Russia.

The scientists also repeated their warnings about North Korea's nuclear and missile tests.