The following correction was printed in the Guardian's Corrections and clarifications column, Friday January 19 2007

Stephen Hawking was mistakenly described as a Nobel laureate in the article below. He is not.





The scientist Stephen Hawking today warned that the world is on the brink of a second nuclear age and a period of unprecedented climate change.

The University of Cambridge mathematician's comments came as the time on the doomsday clock, which counts down to nuclear Armageddon, was moved two minutes closer to midnight, reflecting concerns among scientists over the rise of new nuclear powers.

Climate change was also increasing the threat of catastrophic damage to the planet, academics at the Bulletin Of The Atomic Scientists (BAS) said.

"Since Hiroshima and Nagasaki, no nuclear weapons have been used in war, though the world has come uncomfortably close to disaster on more than one occasion," Prof Hawking said. "But for good luck, we would all be dead.

"As we stand at the brink of a second nuclear age and a period of unprecedented climate change, scientists have a special responsibility once again to inform the public and advise leaders about the perils that humanity faces.

"We foresee great perils if governments and society do not take action now to render nuclear weapons obsolete and prevent further climate change."

Since 1947, the clock - with midnight representing nuclear apocalypse - has appeared on the cover of the BAS with its minute hand moved to reflect the perceived nuclear threat.

The hand's position has been altered 18 times including today's change, which takes the time shown to five to midnight.

Scientists at the magazine, which was founded by University of Chicago physicists alarmed about the dangers of the nuclear age, said people were living in the "most perilous period" since Hiroshima and Nagasaki.

They said the "major step" of moving the hand reflected growing concerns marked by grave threats including the nuclear ambitions of Iran and North Korea and unsecured nuclear materials in Russia and elsewhere.

The move towards increased used of nuclear power to replace fossil fuels, and reduce carbon emissions would increase the risk of nuclear proliferation, they added.

The decision to move the clock forward was reached after discussions with the bulletin's board of sponsors, which includes 18 Nobel laureates.

"North Korea's recent test of a nuclear weapon, Iran's nuclear ambitions, a renewed emphasis on the military utility of nuclear weapons, the failure to adequately secure nuclear materials and the continued presence of some 26,000 nuclear weapons in the United States and Russia are symptomatic of a failure to solve the problems posed by the most destructive technology on Earth," a statement from the board said.

The statement added that the dangers posed by climate change were almost as dire as those posed by nuclear weapons.

"The effects may be less dramatic in the short term than the destruction that could be wrought by nuclear explosions, but over the next three to four decades, climate change could cause irremediable harm to the habitats upon which human societies depend for survival," it added.

Sir Martin Rees, the president of the Royal Society and a professor of cosmology and astrophysics, added: "Nuclear weapons still pose the most catastrophic and immediate threat to humanity, but climate change and emerging technologies in the life sciences also have the potential to end civilisation as we know it."

The closest the clock has come to midnight was at two minutes away in 1953, when the US and Soviet Union tested thermonuclear devices within nine months of each other.

In 1991, in a wave of optimism at the end of the cold war, it was set at its furthest away - 17 minutes to midnight.

It was last moved in February 2002, when, following the terror attacks of events of September 11 2001 and growing concerns over global terrorism, it was pushed forward by two minutes, moving to seven minutes to midnight.

BAS said steps could be taken to reduce the current danger level. These included reducing the launch readiness of US and Russian nuclear forces, dismantling, storing, and destroying more than 20,000 warheads over the next 10 years and stopping the production of nuclear weapons material.

Investments in biofuel and other alternative energies could also reduce the need for new nuclear plants.