California Gov. Jerry Brown, from left, former U.S. Secretary of State George Shultz and former U.S. Secretary of Defense William Perry listen to speakers on a video screen before the unveiling of the “Doomsday Clock,” which measures the likelihood of a global cataclysm, at Stanford University in Stanford, Calif., Tuesday, Jan. 26, 2016.
California Gov. Jerry Brown, from left, former U.S. Secretary of State George Shultz and former U.S. Secretary of Defense William Perry listen to speakers on a video screen before the unveiling of the “Doomsday Clock,” which measures the likelihood of a global cataclysm, at Stanford University in Stanford, Calif., Tuesday, Jan. 26, 2016. Jeff Chiu AP
California Gov. Jerry Brown, from left, former U.S. Secretary of State George Shultz and former U.S. Secretary of Defense William Perry listen to speakers on a video screen before the unveiling of the “Doomsday Clock,” which measures the likelihood of a global cataclysm, at Stanford University in Stanford, Calif., Tuesday, Jan. 26, 2016. Jeff Chiu AP