The world metaphorically edged closer to catastrophe as the Doomsday Clock moved within seconds of midnight - and annihilation.
The clock, which serves as a symbol of global apocalypse, was moved forward by 20 seconds and is now just 100 seconds away from striking 12, scientists said.
The announcement from the clock’s keepers means global threats are now more severe than in 1953, the year the US and the then USSR tested the world's first hydrogen bombs.
Rachel Bronson, president and chief executive of the Bulletin of the Atomic Scientists, which sets the reading, said the clock represented the world now faced a "true emergency" a situation she described as an "absolutely unacceptable state of world affairs that has eliminated any margin for error or further delay".
Former president of Ireland Mary Robinson, chairwoman of The Elders - a non-government organisation of public figures who seek peace - and former UN high commissioner for human rights, described the announcement as a “solemn occasion”.
She said: “We ask world leaders to join us in 2020 as we work to pull humanity back from the brink.
“The Doomsday Clock now stands at 100 seconds to midnight, the most dangerous situation that humanity has ever faced.
“Now is the time to come together – to unite and to act.”
While the clock did not move in 2019, its minute hand was set forward in 2018 by 30 seconds, to two minutes before midnight.
It was adjusted in 2017 to two-and-a-half minutes to midnight from its previous setting of three minutes to midnight.
The countdown was established in 1947 by experts from The Bulletin of the Atomic Scientists who were working on the Manhattan Project to design and build the first atomic bomb.
The bulletin is an independent non-profit organisation run by some of the world’s most eminent scientists.
It was originally intended to warn of the threat of nuclear armageddon.
But the Doomsday Clock also takes into account the likelihood of other emerging threats such as climate change and advances in biotechnology and artificial intelligence.
- What are the three worsening factors that have brought the Doomsday Clock forward
The Bulletin of the Atomic Scientists says that national leaders have "ended or undermined" several major arms control treaties and negotiations in the last year.
They argue this has created an environment conducive to a renewed nuclear arms race, the proliferation of nuclear weapons, and lowered barriers to nuclear war.
The scientists set out that while public awareness of the climate crisis grew over the course of 2019, governmental action fell short of meeting the challenge.
They say: "At UN climate meetings last year, national delegates made fine speeches but put forward few concrete plans to further limit the carbon dioxide emissions that are disrupting Earth's climate.
"This limited political response came during a year when the effects of man-made climate change were manifested by one of the warmest years on record, extensive wildfires, and quicker-than-expected melting of glacial ice."
The misinformation available to the public has heightened the nuclear and climate threats, the bulletin says.
The statement adds that many governments used cyber-enabled disinformation campaigns to sow distrust in institutions and among nations, undermining domestic and international efforts to foster peace and protect the planet.