Doomsday Clock ticks 30 seconds closer to midnight, 'global catastrophe'

WASHINGTON, D.C. -- The Bulletin of Atomic Scientists has moved the minute hand on its Doomsday Clock 30 seconds closer to midnight, which represents the organization's view of the "probability of global catastrophe."

In making the adjustment Thursday, the organization cited the growing threat of climate change, heightening tensions between the United States and Russia, and nuclear proliferation.

For the last two years, the minute hand has been set at three minutes to midnight, but it now sits two-and-a-half minutes away, the closest designation in nearly three decades.

"Wise public officials should act immediately, guiding humanity away from the brink. If they do not, wise citizens must step forward and lead the way," the organization said in a statement.

The decision to move the clock's displayed time is made by the group's science and security board, in consultation with its board of sponsors, which includes 15 Nobel laureates.

ABC News contributed to this report.