Scientists on Tuesday pushed the hands of the infamous "Doomsday Clock" forward one minute from last year, signalling their increasing pessimism about the efforts of world leaders to handle global threats.

"It is now five minutes to midnight," the Bulletin of the Atomic Scientists (BAS) said in a sober assessment of current trends. "Two years ago, it appeared that world leaders might address the truly global threats that we face. In many cases, that trend has not continued or been reversed."

In January 2010, the clock"s minute hand was pushed back one minute from five to six minutes before midnight. Midnight symbolizes humanity"s destruction.

The clock setting, which has been a staple since 1947, represents the severity of the perceived threat to humanity from nuclear or biological weapons, climate change and other human-caused disasters. When it began this annual tradition, the BAS set the time at seven minutes to midnight. Following the first test of the hydrogen bomb, the doomsday clock ticked to two minutes before midnight in 1953. When the United States and Russia began reducing their nuclear arsenals in 1991, the Bulletin set the clock at 17 minutes to midnight.

In explaining its latest move, the BAS bemoaned the ability of global leaders to move ahead on ridding the world of nuclear weapons.

There are about 19,500 nuclear weapons in the world today, according to the BAS, which cautioned that "it is still possible for radical groups to acquire and use highly enriched uranium and plutonium to wreak havoc in nuclear attacks."

It also referenced last year"s accident at Japan"s Fukushima nuclear facility, saying the disaster underscored the urgency of developing safer nuclear reactor designs as well as better oversight, training, and attention.

The gloom did not end there. The Bulletin believes that the world may have neared what it called "a point of no return in efforts to prevent catastrophe from changes in Earth"s atmosphere." It said that in the absence of finding alternatives to carbon-emitting energy technologies within five years," the world will be doomed to a warmer climate, harsher weather, droughts, famine, water scarcity, rising sea levels, loss of island nations, and increasing ocean acidification.

"Unfortunately, Einstein"s statement in 1946 that "everything has changed, save the way we think," remains true," said BAS co-chair Lawrence Krauss. "The provisional developments of 2 years ago have not been sustained, and it makes sense to move the clock closer to midnight, back to the value it had in 2007."