The spectre of a nuclear war 60 years ago was what created the "doomsday clock," the Bulletin of the Atomic Scientists'(BAS) cold war chronometer. The closer the clock to midnight, the closer the world was creeping toward disaster.
These days, the superpower polarisation of the world may be gone, but the threat of nuclear conflict remains. And added to that, a new doomsday force is moving the clock hands: global warming.
Over the six decades of existence, the clock has swung backwards and forwards between 17 minutes to midnight and as close as 2 minutes.
With each new nuclear threat, it ticked closer to twelve. With each new arms reduction treaty or weapons ban, it moved back from the brink. Now both the resurgent threat of nuclear weapons and climate change have moved the hands of the clock two minutes closer: to only 5 minutes away from midnight, the figurative end of the world as we know it.
With the end of the cold war, the clock was at an historic 17 minutes away from midnight in 1991. But since then is has moved steadily closer to midnight with new nuclear threats and now with the addition of climate change.
New nuclear threats are sending the clock back towards the dark days of the nuclear standoff between the US and USSR. These include the nuclear test
which made North Korea an official member of the nuclear weapons club and the incorporation of nuclear weapons into strategic military planning
for a possible US strike against Iran.
"As scientists, we understand the dangers of nuclear weapons and their devastating effects, and we are learning how human activities and technologies are affecting climate systems in ways that may forever change life on Earth.
As citizens of the world, we have a duty to alert the public to the unnecessary risks that we live with every day, and to the perils we foresee if governments and societies do not take action now to render nuclear weapons obsolete and to prevent further climate change."
Stephen Hawking, a BAS sponsor, professor of mathematics at the University of Cambridge, and a fellow of The Royal Society.
Added to the increase in nuclear tensions is the acknowledgment that climate change now represents a new threat that must be faced with the same determination as ending the possibility of nuclear war.
"The Doomsday Clock can go backwards as well as forwards and a massive uptake of renewable energy sources along with energy efficiency and conservation would help us tackle both the climate threat and the threat of spreading dangerous nuclear technology around the world", said Steve Sawyer, Greenpeace climate campaigner.
To reduce the threat of nuclear war requires all governments of the world to listen to their citizens who overwhelmingly reject the use of nuclear weapons. As the world warms and severe weather becomes more frequent across many parts of the world, the solutions to climate change are within the reach of everyone.
Einstein said that with the splitting of the atom everything changed except the way we think: the challenge now is to change the way we act.