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.