The group of scientists who manage the Doomsday Clock - a visual representation of the Earth's risk of imminent disaster - has moved its hands 30 seconds closer to midnight.
They're issuing a warning to the world: humanity is edging closer to the end of life as we know it.
The Bulletin of Atomic Scientists has been issuing warnings to the public since 1947 by way of its so-called Doomsday clock.
It's a symbolic clock where midnight represents the end of the world - Doomsday.
The Executive Director of the Bulletin of Atomic Scientists, Rachel Bronson, says the group has never before moved the clock half a minute closer to midnight.
"The board takes the unprecendented step, the first time in its history, of moving the clock hand 30 seconds closer to midnight. It is now two and a half minutes to midnight."
It's the closest the clock has been to midnight since 1953, the year after competing hydrogen bomb tests by the United States and the Soviet Union.
Ms Bronson says there are two issues that have led to their decision.
"The first has been the cavalier and reckless language used across the globe, especially in the United States during the presidential election and after, around nuclear weapons and nuclear threats. And the second is a growing disregard of scientific expertise, expertise that is needed when it comes to responding to pressing global challenges, including climate change."
The United States and Russia, together responsible for more than 90 per cent of the world's nuclear weapons, remain at odds over major conflicts including Syria, Ukraine and NATO's borders.
Both continue to modernise their nuclear forces instead of negotiating on arms control.
Thomas Pickering is a former US Ambassador and a current member of the Bulletin of Atomic Scientists.
He says North Korea's nuclear weapons ambitions, and growing tensions between Pakistan and India over Kashmir, are also troubling.
"North Korea's continued nuclear weapons development, the steady march of the arsenal modification program in the nuclear weapons states, simmering tension between nuclear-armed India and Pakistan and stagnation in arms control are all of considerable concern."
The scientists also say international efforts to limit global warming have been uneven.
Despite some encouraging signs, such as the Paris agreement on lowering carbon emissions and tackling climate change, they say more needs to be done.
The trend of warm temperatures continue, with 2016 the warmest year on record, as 2015 was before it.
A former head of the US National Oceanic and Atmospheric Administration, David Titley, says there are concerns that proposed candidates for cabinet-level positions in the Trump Administration have expressed scepticism to the climate change threat.
"The current political situation in the United States is of particular concern. The Trump Administration needs to state clearly and unequivocally that it accepts climate change caused by human activity as reality. No problem can be solved unless its existence is first recognised. There are no 'alternative facts' here."
The scientists say the concerns of the scientific community are directly threatened by a growing disregard of scientific expertise, including the expertise of analysts in the global intelligence community.
In his first few days in office, Mr Trump has sought to repair ties with the US intelligence community, and has backed away from some pre-election statements on the United States' nuclear program.
