It is now three minutes to midnight, according to the Bulletin of Atomic Scientists, which is warning that the end of humanity may be nigh. The group behind the famed "Doomsday Clock" announced at a news conference that it was adjusting the countdown to the End of it All by taking away two minutes. It is the closest the clock has been to Doomsday since 1984.

The time is symbolic, sitting at the intersection of art and science, and it has wavered between two minutes and 17 minutes til doom since the clock's inception in 1947. A board of scientists and nuclear experts meets regularly to determine what time it is on the Doomsday Clock.

This time, the clock was adjusted to express the group's dissatisfaction with world progress on "unchecked climate change, global nuclear weapons modernizations, and outsized nuclear weapons arsenals." Those issues, the group said in a statement, "pose extraordinary and undeniable threats to the continued existence of humanity."

The Bulletin of Atomic Scientists was founded by some of the people who worked on the Manhattan Project. One of them, nuclear physicist Alexander Langsdorf, was married to the artist Martyl Langsdorf. She 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 later 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, threatens 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.

Here is every time the Doomsday Clock has moved, and why, according to the Bulletin:

1947: 7 Minutes to Midnight 

The Doomsday Clock is originally set by an artist. The Bulletin says on its site that the image of the clock, on the cover of its magazine, was supposed to capture "the urgency of the nuclear dangers that the magazine's founders -- and the broader scientific community -- are trying to convey to the public and political leaders around the world." 

1949: 3 Minutes to Midnight

Alexander Langsdorf moves the minute hand up by four minutes after a Russian nuclear test. Here's what the magazine said at the time to explain the move: "We do not advise Americans that doomsday is near and that they can expect atomic bombs to start falling on their heads a month or year from now. But we think they have reason to be deeply alarmed and to be prepared for grave decisions."

1953: 2 Minutes to Midnight

The United States tests its first thermonuclear device in October 1952. This is the closest the clock has ever gotten to Doomsday.

1960: 7 Minutes to Midnight

"For the first time, the United States and Soviet Union appear eager to avoid direct confrontation in regional conflicts," the Bulletin says of this move backward from Doomsday. Among other things, the group specifically mentions the formation of several initiatives promoting international scientific cooperation. 

1963: 12 Minutes to Midnight

The United States and the Soviet Union sign the Partial Test Ban Treaty, which bans atmospheric testing of nuclear devices. You can read the full text of that treaty here

1968: 7 Minutes to Midnight

Lots of things contribute to this move: The Vietnam War. The India-Pakistan War of 1965. And nuclear weapons in France and China.

1969: 10 Minutes to Midnight

Most major world powers (but not Israel, India, and Pakistan) sign the Nuclear Non-Proliferation Treaty.

1972: 12 Minutes to Midnight

The United States and Soviet Union sign a pair of treaties aimed at slowing the arms race: The Strategic Arms Limitation Treaty (SALT) and the Anti-Ballistic Missile (ABM) Treaty. 

1974: 9 Minutes to Midnight 

India runs its first test of a nuclear device. And, the Bulletin adds, the United States and Soviet Union continue to modernize their own nuclear capabilities.

1980: 7 Minutes to Midnight

The Bulletin simply cites a lack of progress toward nuclear disarmament for this move, noting that the two global superpowers have "been behaving like what may best be described as 'nucleoholics'--drunks who continue to insist that the drink being consumed is positively 'the last one,' but who can always find a good excuse for 'just one more round.'"

1981: 4 Minutes to Midnight

Russia invades Afghanistan. The United States boycotts the Olympic Games in Moscow. And, the Bulletin notes, Ronald Reagan is elected president. 

1984: 3 Minutes to Midnight 

More pessimism over the state of diplomacy between the United States and the Soviet Union. "Every channel of communications has been constricted or shut down; every form of contact has been attenuated or cut off. And arms control negotiations have been reduced to a species of propaganda," writes the Bulletin.

1988: 6 Minutes to Midnight

Ronald Reagan and Mikhail Gorbachev have signed the Intermediate-Range Nuclear Forces Treaty, which bans a specific type of nuclear weapon. 

1990: 10 Minutes to Midnight

The Berlin Wall falls, and Poland, Czechoslovakia, Hungary and Romania break out from Soviet control. 

1991: 17 Minutes to Midnight

This is the farthest the clock's minute hand has been from doomsday, indicating the group's momentary optimism at the official end of the Cold War.

1995: 14 Minutes to Midnight

Maybe we were a little too optimistic, the Bulletin says. The group notes at the time that there are more than 40,000 nuclear weapons around the world.

1998: 9 Minutes to Midnight

Russia and the United States still have nuclear warheads aimed at each other, and India and Pakistan conduct rival nuclear tests.

2002: 7 Minutes to Midnight 

America withdraws from the Anti-Ballistic Missile Treaty, 20 years after it was signed. The Bulletin's board is also concerned about "the enormous amount of unsecured -- and sometimes unaccounted for -- weapon-grade nuclear materials," as speculation spreads about the possibility of a nuclear terrorist attack.

2007: 5 Minutes to Midnight 

North Korea tests a nuclear weapon, and the West is worried that Iran wants one, too. For the first time, the Bulletin mentions a second concern: climate change.

The United States and Russia are in talks to renew something akin to the Strategic Arms Reduction Treaty, and the Bulletin is slightly more optimistic on international efforts to combat climate change. 

2012: 5 Minutes to Midnight 

"The challenges to rid the world of nuclear weapons, harness nuclear power, and meet the nearly inexorable climate disruptions from global warming are complex and interconnected. In the face of such complex problems, it is difficult to see where the capacity lies to address these challenges," the Bulletin writes. 

2015: 3 Minutes to Midnight.

Speaking of nuclear weapons modernization, climate change and the continued existence of nuclear weapons arsenals, the Bulletin writes that "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.”

Read more from Speaking of Science: