The Bulletin of the Atomic Scientists advanced the symbolic Doomsday Clock a notch closer to the end of humanity Thursday, moving it ahead by 30 seconds. It is now set at two minutes to "midnight."

In moving the clock 30 seconds closer to the hour of the apocalypse, the Bulletin of the Atomic Scientists cited "the failure of President Trump and other world leaders to deal with looming threats of nuclear war and climate change."

The organization now believes "the world is not only more dangerous now than it was a year ago; it is as threatening as it has been since World War II," Bulletin officials Lawrence M. Krauss and Robert Rosner wrote in an op-ed published Thursday by The Washington Post. "In fact, the Doomsday Clock is as close to midnight today as it was in 1953, when Cold War fears perhaps reached their highest levels."

Krauss, a theoretical physicist, and Rosner, an astrophysicist, added: "To call the world nuclear situation dire is to understate the danger - and its immediacy. North Korea's nuclear weapons program appeared to make remarkable progress in 2017, increasing risks for itself, other countries in the region and the United States."

The clock, a metaphorical measure of humankind's proximity to global catastrophe, also advanced 30 seconds last year, to 2 1/2 minutes to "midnight" - the closest to the apocalyptic hour it has been since 1953, after the United States tested its first thermonuclear device, followed months later by the Soviet Union's hydrogen bomb test.

Before Thursday's announcement, experts said there was only one direction the clock could possibly move, given recent geopolitical events - including North Korea's intercontinental ballistic missile test and the my-nuclear-button-is-bigger-than-yours war of words between Trump and North Korean leader Kim Jong Un.

"I think it would be very hard for the clock not​ to move forward," Alex Wellerstein, who specializes in the history of nuclear weapons at the Stevens Institute of Technology, said in an email leading up to the announcement. "We have members of Congress, White House advisers, and even the president implying that they think war with a nuclear state is not only likely, but potentially desirable. That's unusual and disturbing.

"The question I have is: How much forward can they go?"

Another 30 seconds, to be exact.

The clock is symbolic, sitting at the intersection of art and science, and it has wavered between two and 17 minutes until doom since its inception in 1947.

A board of scientists and nuclear experts meets regularly to determine what time it is on the Doomsday Clock. This group, called the Bulletin of the Atomic Scientists, was founded by veterans of the Manhattan Project concerned about the consequences of their nuclear research. One of them, nuclear physicist Alexander Langsdorf, was married to artist Martyl Langsdorf, who created the clock and set it at seven minutes to midnight, or 11:53, for the cover of the group's magazine. Her husband moved the time four minutes ahead in 1949.

Since then, the bulletin's board has determined when the clock's minute hand will move, usually to draw attention to worldwide crises that, the board believes, threaten the survival of the human species. The group's reasoning focuses almost exclusively on the availability of nuclear weapons and a willingness among the world's great powers to use them.

"Whenever the clock is set, we answer two basic questions," Rachel Bronson, president of the Bulletin, said in an interview last fall. "Is the world safer, or at greater risk than it was a year ago? And is it safer or at greater risk than it was ever in the clock's history?"

The group's reasoning has traditionally focused on the availability of nuclear weapons and a willingness among the world's great powers to use them. But in recent years, the scientists have also considered the threat posed by climate change, which they said in 2007 is "nearly as dire" as the dangers of nuclear weapons.

In advancing the famed clock last year, the group noted that "the global security landscape darkened as the international community failed to come effectively to grips with humanity's most pressing existential threats, nuclear weapons and climate change."

But the organization also cited the election of Trump - "who has promised to impede progress on both of those fronts," Krauss and retired Navy Rear Adm. David Titley wrote in an op-ed last year. "Never before has the Bulletin decided to advance the clock largely because of the statements of a single person. But when that person is the new president of the United States, his words matter."

Daryl Kimball, executive director of the nonprofit Arms Control Association, said a symbolic move toward "midnight" makes sense - and that nuclear risks alone justified it.

"Over the year, there has been increased tensions with North Korea, nuclear threats conveyed by President Trump and Kim Jong Un, tensions with Russia are higher - perhaps as difficult as they have been since the end of the Cold War," he said Wednesday. Within days, Kimball noted, the Trump administration is set to announce a nuclear strategy that calls for expanding the role of U.S. nuclear weapons. "So the risk of a nuclear conflict by accident or by design is unfortunately growing higher," he added.

In a September speech at the United Nations, Trump threatened to "totally destroy North Korea" to defend the United States or its allies, and referred to Kim by the new nickname he had just given the dictator on Twitter, saying: "Rocket Man is on a suicide mission for himself."

Trump tweeted "I spoke with President Moon of South Korea last night. Asked him how Rocket Man is doing. Long gas lines forming in North Korea. Too bad!"

Trump tweeted "Just heard Foreign Minister of North Korea speak at U.N. If he echoes thoughts of Little Rocket Man, they won't be around much longer!"

Kim responded with an arcane insult, declaring in an unusually direct and angry statement published by North Korea's official Korean Central News Agency: "I will surely and definitely tame the mentally deranged U.S. dotard with fire." (Oxford defines dotard as "an old person, especially one who has become weak or senile.")