The Bulletin of Atomic Scientists moved the clock forward to 90 seconds to midnight “largely, not exclusively, because of the mounting dangers in the war in Ukraine”, the scientists said during Tuesday's announcement.
"We are living in a time of unprecedented danger and the Doomsday Clock time reflects that reality," said Bulletin of Atomic Scientists president Rachel Bronson.
The clock had remained unchanged at 100 seconds to midnight for the past three years.
"Ninety seconds to midnight is the closest the clock has ever been set to midnight, and it’s a decision our experts do not take lightly," Ms Bronson said.
Scientists last year said the decision to keep the clock level did not indicate “the international security situation has stabilised”.
Many of the existential threats to humanity listed by the atomic scientists last year remain today.
Russia's February 24 invasion of Ukraine and the subsequent war have heightened the risks to global stability. President Vladimir Putin has deepened fears of potential nuclear war by issuing threats that he would be willing to use such weapons.
With the war dragging on past its 11th month with no end in sight, the Bulletin said the US, Nato and Ukraine have "multiple channels for dialogue".
"We urge leaders to explore all of them to their fullest ability to turn back the Clock," Ms Bronson said.
Meanwhile, North Korea's leader Kim Jong-un announced plans to “exponentially” increase his country's nuclear weapons. Pakistan and Iran also continue to expand their own nuclear arsenals, the of Bulletin Atomic Scientists said.
“Nuclear weapons remind the world that escalation of the conflict by accident intention or miscalculation is a terrible risk,” Ms Bronson said.
During the past 12 months, many destructive climate events have occurred around the world.
Europe and the Middle East experienced record-breaking heat, the US was plagued by deadly hurricanes and fires, more than 1,000 people in Afghanistan were killed in an earthquake, and India and Pakistan were ravaged by flooding.
World leaders offered some hope in the fight against climate change by reaching a historic agreement at Cop27 in Egypt.
A “loss and damage fund” was created to provide nations most vulnerable to climate change with financial assistance.
The Doomsday Clock was designed in 1947 to document how close humanity was to its own destruction.