'Doomsday Clock' moves a minute back
The concept timepiece, devised by the Bulletin of the Atomic Scientists (BAS) now stands at six minutes to the hour.
The group said it made the decision to move the clock back because of a more "hopeful state of world affairs".
The clock was first featured by the magazine in 1947, shortly after the US dropped its A-bombs on Japan.
The clock had been adjusted 18 times before today since its initial start at seven minutes to midnight.
Most recently, in January 2007, the clock moved to five minutes to midnight, when climate change was added to the prospect of nuclear annihilation as the greatest threats to humankind.
The concerns then included Iran's nuclear ambitions and the inability to halt the international trafficking of nuclear materials such as highly enriched uranium and plutonium.
Two years later, however, the board of the BAS says that there is now a "growing political will" to tackle both the "terror of nuclear weapons" and "runaway climate change".
At a news conference in New York, the BAS board said: "By shifting the hand back from midnight by only one additional minute, we emphasize how much needs to be accomplished, while at the same time recognizing signs of collaboration among the United States, Russia, the European Union, India, China, Brazil, and others on nuclear security and on climate stabilization."
But Lawrence Krauss, co-chair of the BAS board of sponsors, warned scientists that there was still much to be done.
"We urge leaders to fulfill the promise of a nuclear weapon-free world and to act now to slow the pace of climate change," he said.
"We are mindful of the fact that the clock is ticking," he added.
The Bulletin of the Atomic Scientists, founded by former Manhattan Project physicists, has campaigned for nuclear disarmament since 1947.
Its board periodically reviews issues of global security and challenges to humanity, not solely those posed by nuclear technology, although most have had a technological component.