Citing unchecked climate change and the ongoing threat of nuclear weapons, scientists Thursday moved the hands of the Doomsday Clock two minutes closer to midnight.

"It is now three minutes to midnight," said Kennette Benedict, the executive director and publisher of the Bulletin of the Atomic Scientists at a news conference in Washington, D.C. "The probability of global catastrophe is very high. This is about the end of civilization as we know it."

Three minutes is the closest to midnight the clock has been since 1984 during the Cold War. The closest it has ever been to midnight — two minutes— was in 1953, when the hydrogen bomb was first tested. The closer to a setting of midnight it gets, the closer it's estimated that a global disaster will occur.

"In 2015, unchecked climate change, global nuclear weapons modernizations and outsized nuclear weapons arsenals pose extraordinary and undeniable threats to the continued existence of humanity," the Bulletin of the Atomic Scientists said in a statement.

"World leaders have failed to act with the speed or on the scale required to protect citizens from potential catastrophe. These failures of political leadership endanger every person on Earth."

The clock is symbolic and has been maintained by the Bulletin of the Atomic Scientists since 1947. The group was founded in 1945 by University of Chicago scientists who had helped develop the first nuclear weapons in the Manhattan Project.

The scientists created the clock in 1947 using the imagery of apocalypse (midnight) and the contemporary idiom of nuclear explosion (countdown to zero), to convey threats to humanity and the Earth.

Before Thursday, the Doomsday Clock was most recently moved ahead from six to five minutes to midnight in 2012, also in a response to nuclear proliferation and climate change.

"Human influence on the climate system is clear," Richard Somerville of the Bulletin said at the conference Thursday. "Each of the last three decades has been successively warmer than any preceding on record."

USA Today