The Doomsday Clock is a symbol that represents the likelihood of a man-made global catastrophe. Maintained since 1947 by the members of the Bulletin of the Atomic Scientists, the Clock is a metaphor for threats to humanity from unchecked scientific and technical advances. The Clock represents the hypothetical global catastrophe as "midnight" and the Bulletin's opinion on how close the world is to a global catastrophe as a number of "minutes" or "seconds" to midnight, assessed in January of each year. The main factors influencing the Clock are nuclear risk and global warming (climate change). The Bulletin's Science and Security Board also monitors new developments in the life sciences and technology that could inflict irrevocable harm to humanity.