The Doomsday Clock, a symbolic indicator made famous by the Bulletin of Atomic Scientists since its inception in 1947, was moved Tuesday from six minutes to five minutes before midnight as a warning about nuclear dangers and climate change.
"Despite the promise of a new spirit of international cooperation, and reductions in tensions between the United States and Russia, the Science and Security Board believes that the path toward a world free of nuclear weapons is not at all clear, and leadership is failing," the group said in its statement explaining the move.
The group also cited Japan's nuclear reactor disaster last year as a concern. "A major question to be addressed is: How can complex systems like nuclear power stations be made less susceptible to accidents and errors in judgment?"
The Bulletin of Atomic Scientists was founded in 1945 by University of Chicago scientists who helped develop the first atomic weapons.
The clock was not moved in 2011; in 2010 it was moved back one minute.
On climate, the group noted that "the International Energy Agency projects that, unless societies begin building alternatives to carbon-emitting energy technologies over the next five years, the world is doomed to a warmer climate, harsher weather, droughts, famine, water scarcity, rising sea levels, loss of island nations, and increasing ocean acidification."
Arizona State University Physics Professor Lawrence Krauss, a Bulletin member, summed up the group's thoughts as pessimistic.
"Faced with clear and present dangers of nuclear proliferation and climate change, and the need to find sustainable and safe sources of energy, world leaders are failing to change business as usual," he said. "Inaction on key issues including climate change, and rising international tensions motivate the movement of the clock."
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