NEW YORK (Reuters) - Scientists pushed back the hands on the symbolic Doomsday Clock by one minute citing hopeful developments in nuclear weapons and climate change.

The symbolic clock that shows how close mankind is to self-annihilation was moved back to six minutes before midnight from five minutes on Thursday.

The Bulletin of Atomic Scientists, which maintains the clock and puts an illustration of it on its cover, attributed the move to efforts by world leaders to reduce their countries' nuclear arsenals and collaborate on climate stabilization.

The group, which includes 19 Nobel laureates, said a key to the "new era of cooperation is a change in the U.S. government's orientation toward international affairs brought about in part by the election of (U.S. President Barack) Obama."

Nuclear physicist Pervez Hoodbhoy at news conference held at the New York Academy of Sciences overlooking the World Trade Center site, said there had been "a shift in world opinion" recognizing that nuclear weapons are "no longer useful to fight wars and are not effective as deterrence."

BAS board member Lowell Sachnoff added, "Global warming is more of a threat than nuclear war."

When the clock was created in 1947, it was set at 7 minutes to midnight. It has been adjusted only 18 times before Thursday' move. The last was in 2007, when the BAS moved it forward by two minutes citing North Korea's test of a nuclear weapon, Iran's nuclear ambitions and a renewed U.S. emphasis the military utility of nuclear weapons.