The Doomsday Clock has ticked a minute closer to midnight.
The Bulletin of Atomic Scientists, which created the clock in 1947 as a barometer of how close the world is to an apocalyptic end, says it is now five minutes to midnight.
The last time the clock was changed, in 2010, the scientists moved it back a minute on hopes of global nuclear cooperation and the election of United States president Barack Obama, AFP reports.
However, the latest decision - based on global uncertainty over how to deal with the threats of nuclear weapons, climate change, and a growing tendency to reject science when it comes to major world concerns - pushes it back to where it was in 2007.
Robert Socolow, a member of the group's science and security board and professor of mechanical and aerospace engineering at Princeton University called for better world political leadership that accepts the role of science.
The group said it was "heartened by" a series of world protest movements, including the Arab spring, the Occupy demonstrations in the US and protests in Russia, which showed people were seeking a greater say in their future.
The nuclear accident at Japan's Fukushima plant also highlighted the volatility of relying on nuclear power in areas prone to natural disasters, scientists said.
The clock reached its most perilous point in 1953, at two minutes to midnight, after the US and the Soviet Union tested thermonuclear devices within nine months of one another.