Doomsday Clock

At its highest point (1991), it was 17 minutes to midnight; at its lowest (1962, and again in 2018), it was 2 minutes. As of January 2019, the clock stands at two minutes until midnight.

"And When the Clock Strikes Twelve tell me where ya gonna be?
Cleaning up the mess we've made or watching your TV?"

—Billy Talent, "Turn Your Back"

The Doomsday Clock is a symbolic clock face maintained by the Bulletin of the Atomic Scientists at the University of Chicago. When it was originally introduced in 1947 the clock symbolized how close the world was to nuclear war, with the metaphor supporting it being: talks have broken down, and once midnight hits, the attacks start. And we are all doomed. But since the fall of the Iron Curtain, the original metaphor is (mostly) obsolete, and it has expanded to catastrophic destruction of any sort, provided it's on a global scale; the Bulletin's website specifically mentions global warming and bioengineering as possible causes in addition to nuclear war. The Doomsday Clock is a very real and very eerie example of When the Clock Strikes Twelve and as such, it has received nods by several works.

The Doomsday Clock is updated periodically by the Bulletin, however the changes do not always occur in time with world events. Most notably, the Cuban Missile Crisis, which was the closest the Cold War got to open nuclear conflict, reached its climax and was resolved before the Clock could be changed. The closest it's been was 2 minutes to midnight from 1953-1960, and again in 2018, while the farthest was 17 minutes from 1991-1995. In January 2018, it moved up to two minutes to midnight in response to nuclear brinksmanship between North Korea and the United States, escalating tensions elsewhere in the world, and accelerating effects of climate change, among other factors. The clock remained at 2 minutes to midnight in 2019, a situation that the Bulletin of the Atomic Scientists's CEO Rachel Bronson called a "new abnormal".

As mentioned, this is a subtrope of When the Clock Strikes Twelve. Compare: Death's Hourglass which could be this for a single person.

Examples of Doomsday Clock include:

Comic Books

A recurring motif in Watchmen with the clock gradually ticking towards midnight until the end. It is also mentioned directly with the clock being at five minutes near the beginning. Ironically, this is actually further from midnight than the real-life clock was in the early to mid-1980s.
- The clock is seen more often as the best-known symbol of the series: the Comedian's smiley-face badge. If you look at it with both eyes pointing up, the bloody smear resembles a minute hand pointing at 11 on a clock. This was actually the entire point of the design, to dress up something happy to something terrifying, with one tiny change.

Film

Dr. Strangelove or: How I Learned To Stop Worrying And Love The Bomb has this.^{[please verify]}

Literature

In Piers Anthony's novel Wielding a Red Sword, the Incarnation of War can use the Doomsday Clock to bring about World War III.

Live-Action TV

Doctor Who had an episode called Four to Doomsday, which was released when the real life clock was at four minutes.
The Heroes episode Seven to Midnight revolved around stopping a nuclear bomb from going off in New York City. At the time it was aired the clock stood at seven minutes.
NCIS episode Murder 2.0 had the Doomsday Clock, at the time set to five minutes, used as a clue to indicate the next murder would take place at 11:55 p.m.
Lost reveals in later seasons that the repeated number sequence, 4 8 15 16 23 42 is in fact a component of an insanely accurate Doomsday Clock: the Valenzetti Equation, which predicts the extinction of mankind, with the Numbers serving as the input.
The second to last episode of Supernatural season 5 is called "Two Minutes to Midnight". "Midnight" in this case referring to the rise of Lucifer on earth, who did show up in the last episode of season 5.

Music

"2 Minutes to Midnight" by Iron Maiden.
"Doomsday Clock" by The Smashing Pumpkins.
Linkin Park's album Minutes to Midnight. The music video for "Shadow of the Day" from the same album also makes reference to the clock with 11:55 appearing at the beginning.
"11:59" by Blondie.
"The Call Up" by The Clash has the lyric "55 minutes past eleven.
Likewise, "Turn Your Back" by Billy Talent has the lyric "When the clock strikes twelve, tell me where ya gonna be?" at the beginning. The entire song makes reference to disasters occurring and hoping the world can change.
"4 Minutes (To Save the World)" by Madonna.
"One Minute to Midnight" by Justice.
"Particle Man" by They Might Be Giants has an inversion with Universe Man's watch, that seems to measure the age of the cosmos:

"He has a watch with a minute hand, a millennium hand, and an eon hand - and when they meet, it's a happy land! Powerful man, Universe Man."

Video Games

While not an exact representation, Rise of Nations has an example clearly based on the Doomsday Clock. When a player researches nuclear weapons, a counter appears on his HUD. Every time any player uses a nuke, it goes down by 1. If it reaches zero, the game ends with everyone losing as the clock strikes midnight.

Web Comics

Homestuck has a doomsday clock near Terezi's home.

Western Animation

One episode of Adventures of the Gummi Bears featured a Doomsday Clock built by an evil sorcerer, which would actually destroy the world if it ever struck twelve - unless, of course, it was destroyed first.