The keepers of a symbolic Doomsday Clock - a world-famous symbol designed by the US-based Bulletin of Atomic Scientists to chart how close we are to Armaggedon - have announced they are moving its hands forward.

According to the University of Chicago-based organisation, worsening climate change and the increasing threat of nuclear war are threatening our survival. The clock's hands will be moved forward next Wednesday.

The clock, which has appeared on the Bulletin of Atomic Scientists magazine's front cover since 1947, is currently set at seven minutes to midnight - with midnight marking global catastrophe.

In a news release previewing next Wednesday's event, which will be co-hosted by the British physicist Stephen Hawking, the organisation would not say exactly how far the clock would be moved forward - but explained that a change was necessary because of "worsening nuclear, climate threats" to the world.

"The major new step reflects growing concerns about a 'Second Nuclear Age' marked by grave threats, including: nuclear ambitions in Iran and North Korea, unsecured nuclear materials in Russia and elsewhere, the continuing 'launch-ready' status of 2,000 of the 25,000 nuclear weapons held by the US and Russia; escalating terrorism; and new pressure from climate change for expanded civilian nuclear power that could increase proliferation risks," it said.

The clock was last pushed forward by two minutes to seven minutes to midnight in 2002, amid concerns about the proliferation of nuclear, biological and other weapons and the threat of terrorism in the aftermath the attacks on September 11, 2001.

The last time it was closer than that to midnight was in 1988, when the Cold War was beginning to show its first signs of coming to an end and the clock showed 11.54pm.

With the time set to be put forward again, it is inevitable that it will be at a closer point to midnight than at any time since that year - and perhaps closer.

When it was created by the magazine's staff in 1947, it was initially set at seven minutes to midnight and has moved 17 times since then.

It was as close as two minutes to midnight in 1953 following U.S. and Soviet hydrogen bomb tests - and as far away as 17 minutes to midnight in 1991 in a wave of optimism as the Soviet