It is getting closer to midnight.
On Thursday, the group of scientists who orchestrate the Doomsday Clock, a symbolic instrument informing the public when the earth is facing imminent disaster, moved its minute hand from three to two and a half minutes before the final hour.
It was the closest the clock had been to midnight since 1953, the year after the United States and the Soviet Union conducted competing tests of the hydrogen bomb.
Though scientists decide on the clock’s position, it is not a scientific instrument, or even a physical one. The movement of its symbolic hands is decided upon by the Science and Security Board of the Bulletin of the Atomic Scientists. The organization introduced the clock on the cover of its June 1947 edition, placing it at seven minutes to midnight. Since then, it has moved closer to midnight and farther away, depending on the board’s conclusions.
Thursday’s announcement was made by Rachel Bronson, the executive director and publisher of the bulletin. She was assisted by the theoretical physicist Lawrence Krauss, the climate scientist and meteorologist David Titley, and the former United States ambassador Thomas Pickering.
Ms. Bronson, in a post-announcement interview, explained why the board had included the 30 second mark in the measurement. She said that it was an attention-catching signal that was meant to acknowledge “what a dangerous moment we’re in, and how important it is for people to take note.”
“We’re so concerned about the rhetoric, and the lack of respect for expertise, that we moved it 30 seconds,” she said. “Rather than create panic, we’re hoping that this drives action.”
In an op-ed for The New York Times, Mr. Titley and Mr. Krauss elaborated on their concerns, citing the increasing threats of nuclear weapons andclimate change, as well as President Trump’s pledges to impede what they see as progress on both fronts, as reasons for moving the clock closer to midnight.
“Never before has the Bulletin decided to advance the clock largely because of the statements of a single person,” they wrote. “But when that person is the new president of the United States, his words matter.”
The board has held the responsibility for the clock’s movements since 1973, when the bulletin’s editor, Eugene Rabinowitch, died. Composed of scientists, and nuclear and climate experts, the board meets biannually to discuss where the clock’s hands should fall in light of world events.
In the 1950s, the scientists feared nuclear annihilation, and since then, the board has begun to consider other existential threats, including climate change, compromised biosecurity and artificial intelligence.
There were crises that the clock was not quick enough to take into account. The Cuban Missile Crisis, for instance, in 1962, did not change the hands of the clock, which at the time stood at seven minutes to midnight.
An explanation on the Bulletin’s website accounts for this seeming lapse in timekeeping: “The Cuban Missile Crisis, for all its potential and ultimate destruction, only lasted a few weeks,” it says. “However, the lessons were quickly apparent when the United States and the Soviet Union installed the first hotline between the two capitals to improve communications, and, of course, negotiated the 1963 test ban treaty, ending all atmospheric nuclear testing.”
The end of the Cold War came as a relief to those who had lived in fear of nuclear annihilation for decades, and the minute hand slowly moved away from danger. In 1990, it was at 10 minutes to midnight. The next year, it was a full 17 minutes away, at the relatively undisturbing time of 11:43.
“The illusion that tens of thousands of nuclear weapons are a guarantor of national security has been stripped away,” the Bulletin said at the time.
But over the next two decades the clock slowly ticked back. Conflict between India and Pakistan, both of whom staged nuclear weapons tests three weeks apart, had the clock at nine minutes to midnight in 1998. By 2007, fears about Iranian and North Korean nuclear capacity had pushed it to 11:55.
By 2015, the scientists were back in a state of unmitigated concern, with the clock at three minutes to midnight, the closest it had been since 1984.
“Unchecked climate change, global nuclear weapons modernizations, and outsized nuclear weapons arsenals pose extraordinary and undeniable threats to the continued existence of humanity,” the bulletin said. “World leaders have failed to act with the speed or on the scale required to protect citizens from potential catastrophe.”
“These failures of political leadership endanger every person on Earth,” it added.