The ominous hands of the "Doomsday Clock" have been fixed at 5 minutes to midnight for the past three years. But they could move tomorrow.

The clock is a visual metaphor that was created nearly 70 years ago by The Bulletin of the Atomic Scientists. Each year, the magazine's board assesses threats to humanity — with special attention to nuclear warheads and climate change — to decide whether the Doomsday Clock needs an adjustment. The closer the hands are to midnight, the closer the world is to a potentially civilization-ending catastrophe.

Tomorrow (Jan. 22), at a news conference in Washington, D.C., The Bulletin of the Atomic Scientists will announce where the hands will rest for 2015. [End of the World? Top Doomsday Fears]

In 1945, shortly after the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki, a group of Manhattan Project scientists from the University of Chicago created The Bulletin of the Atomic Scientists, with a mission to help educate the public about the dangers of nuclear weapons. Two years later, the group came up with the idea for the Doomsday Clock. Martyl Langsdorf, a painter and wife of one of the scientists who worked on the Manhattan Project, illustrated the clock for the magazine cover. At the time, it was set at 11:53 p.m.

In 1953, the clock was set at 11:58 p.m., the closest it's ever been to midnight, after both the United States and the Soviet Union conducted their first tests of the hydrogen bomb. The clock's hands retreated to 11:43 p.m., 17 minutes to midnight, in December 1991, after the world's nuclear superpowers signed the Strategic Arms Reduction Treaty. But since then, the board's outlook has only been grimmer.

In January 2012, the clock's hands were pushed to 11:55 p.m., 1 minute closer to midnight than the previous year. At the time, the board was particularly concerned about the nuclear meltdown in Japan's Fukushima power plant and the creation of an airborne strain of H5N1 influenza virus. In 2013 and 2014, the clock's hands didn't budge.

As in past years, the board said climate change and nuclear warheads are the two major threats in 2015 that will influence its decision to move the hands of the clock. In a statement, the board listed some events in the past year that have influenced their deliberations: a worrying report in November 2014 from the Intergovernmental Panel on Climate Change (IPCC); "inadequate" international action to cut greenhouse gas emissions during recent U.N. climate talks in Lima, Peru; and a lack of progress in the United States and Russia to shrink nuclear arsenals.

Tomorrow's event will be broadcast live on the magazine's website at 11 a.m. EST (1600 GMT).

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