The Doomsday Clock indicates the likelihood of an atomic holocaust or catastrophe. The closer the clock moves toward midnight, the higher the probability that civilization is to be destroyed by weapons of mass destruction, according to the Bulletin of the Atomic Scientists. The Bulletin first established the clock in 1947, responding to the growing nuclear threat, evidenced by the nuclear bombing of Hiroshima and Nagasaki, and has maintained it since.
The Science and Security Board of the Bulletin of the Atomic Scientists meets twice each year to determine if the hands of the clock need to be moved. and, if so, whether they need to be moved closer to midnight, signaling human behavior threatening the safety of the world, or backward, signalling the decrease in some world-threatening tension.
For many years, the primary concern was the nuclear weapon, with the hands being at their closest, two minutes to midnight, in 1953. As Cold War and nuclear tensions decreased, human impacts, such as climate change, became deciding factors in the movement of the hands closer to midnight. As of 2014, the last move was in 2012 to five minutes to midnight, citing an ineffective response to the development of new nuclear weapons, failures of nuclear power and climate disruptions as reasons for the shift toward the figurative end of times.