The Doomsday Clock is a design that warns the public about how close we are to destroying our world with dangerous technologies of our own making. It is a metaphor, a reminder of the perils we must address if we are to survive on the planet.

When the Doomsday Clock was created in 1947, the greatest danger to humanity came from nuclear weapons, in particular from the prospect that the United States and the Soviet Union were headed for a nuclear arms race. The Bulletin considered possible catastrophic disruptions from climate change in its hand-setting deliberations for the first time in 2007.

Co-editor Hyman Goldsmith asked artist Martyl Langsdorf to come up with a design for the cover of the June 1947 edition of the Bulletin, the first issue published as a magazine rather than a newsletter. Martyl—as she was known professionally—was married to a physicist, Alexander Langsdorf, who worked on the Manhattan Project while at the University of Chicago.

At first the artist considered using the symbol for uranium. But as she listened to the scientists who had worked on the Bomb, as they passionately debated the consequences of the new technology and their responsibility to inform the public, she felt their sense of urgency. So she sketched a clock to suggest that we didn’t have much time left to get atomic weapons under control.

Graphic designer Michael Bierut reimagined the iconic image in 2007.

In the early days, Bulletin Editor Eugene Rabinowitch decided whether the hand should be moved. A scientist himself, fluent in Russian, and a leader in the international disarmament movement, he was in constant conversation with scientists and experts within and outside governments in many parts of the world. Based on these discussions, he decided where the clock hand should be set and explained his thinking in the Bulletin’s pages.

When Rabinowitch died in 1973, the Bulletin’s Science and Security Board took over the responsibility and has since met twice a year to discuss world events and reset the clock as necessary. The board is made up of scientists and other experts with deep knowledge of nuclear technology and climate science, who often provide expert advice to governments and international agencies. They consult widely with their colleagues across a range of disciplines and also seek the views of the Bulletin’s Board of Sponsors, which includes 13 Nobel Laureates.

In 1991, with the end of the Cold War, the United States and the Soviet Union signed the Strategic Arms Reduction Treaty, the first treaty to provide for deep cuts to the two countries’ strategic nuclear weapons arsenals, prompting the Bulletin to set the clock hand to 17 minutes to midnight.