The minute hand of the famous Doomsday Clock will be moved at 3pm tomorrow afternoon, for the first time in two years.
The timepiece in New York conveys how close humanity is to catastrophic destruction, which is represented by midnight.
It was created by the Bulletin of the Atomic Scientists in 1947, two years after the U.S dropped the first atomic bombs on Japan in World War II. It was originally set at seven minutes to midnight.
The clock has been altered 18 times since then by the Bulletin's scientific board. This now includes Professor Stephen Hawking and 18 other Nobel laureates.
The latest recorded time was two minutes to midnight in 1953 as the Cold War heated up between the U.S and Soviet Union.
In 2007 it was wound on to five minutes to midnight, to reflect the failure to solve problems posed by nuclear weapons.
Today the public can watch the change for the first time via a live web feed.
A spokesman said: 'Factors influencing the latest Doomsday Clock change include international negotiations on nuclear disarmament and nonproliferation, expansion of civilian nuclear power, the possibilities of nuclear terrorism, and climate change.'
Just last month environmentalists criticised the Copenhagen Climate Change Conference, after leaders failed to reach any real consensus.