WASHINGTON, DC - JANUARY 26:  (L-R) Stockholm Environment Institute Senior Scientist Sivan Kartham, Center for Strategic and International Studies' Proliferation Prevention Program Director Sharon Squassoni and Arizona State University New Origins Initiative Director Lawrence Krauss simultaneously unveil the Doomsday Clock with other scientists in California during a news conference at the National Press Club January 26, 2016 in Washington, DC. The  bulletin's Science and Security Board takes into consideration "the number and kinds of nuclear weapons in the world, the parts per million of carbon dioxide in the atmosphere, the degree of acidity in our oceans and the rate of sea level rise" when setting the clock as a warning against self-destruction.  (Photo by Chip Somodevilla/Getty Images)