The Doomsday Clock is a symbolic clock face, representing a countdown to possible global catastrophe (e.g. nuclear war or climate change). It has been maintained since 1947 by the members of the Science and Security Board of the Bulletin of the Atomic Scientists, who are in turn advised by the Governing Board and the Board of Sponsors, including 18 Nobel Laureates.
The closer they set the Clock to midnight, the closer the scientists believe the world is to global disaster.
Originally, the Clock, which hangs on a wall in the Bulletin’s office in the University of Chicago, represented an analogy for the threat of global nuclear war; however, since 2007 it has also reflected climate change and new developments in the life sciences and technology that could inflict irrevocable harm to humanity.
The most recent officially announced setting—three minutes to midnight (11:57 pm)—was made on January 22, 2015 due to climate change, the modernization of nuclear weapons in the United States and Russia, and the problem of nuclear waste.
As of mid-2014, the authors estimate that there are approximately 16,300 nuclear weapons located at some 98 sites in 14 countries.
Roughly 10,000 of these weapons are in military arsenals; the remaining weapons are retired and awaiting dismantlement. Approximately 4,000 are operationally available, and some 1,800 are on high alert and ready for use on short notice.
The largest concentrations of nuclear weapons reside in Russia and the United States, which possess 93 percent of the total global inventory. The United States today stores nuclear weapons at 18 sites, including 12 sites in 11 states in the United States and another six sites in five European countries.
There is considerable uncertainty about the number of Russian nuclear weapons storage sites, but the authors estimate that Russia today stores nuclear weapons permanently at 40 domestic locations.