The Bulletin of the Atomic Scientists has moved the Doomsday Clock ahead 30 seconds, taking the world to 2½ minutes to midnight.

This clock was first used in 1947 as a measure of how close humanity is to destroying our civilization. It typically moves by the minute. This is the first time it has moved by 30 seconds.

Clock ticks closer to midnight, as the Bulletin of the Atomic Scientists sees an increase in dangers to humanity, from climate disruption to nuclear war 2:51

The scientists said Thursday that several factors weighed heavily in their decision, particularly climate change denial by people in power — they cited U.S. President Donald Trump — and talk about more nuclear weapons.

"This is the first time the words and stated policy of one or two people placed in high positions has had such an impact to our perception of existential threat," said scientist Lawrence Krauss.

The scientists named both Donald Trump and Russian leader Vladimir Putin as their chief concerns, but also pointed to leaders of Pakistan and North Korea.

Trump has denied that climate change is occurring and has also called for the U.S. to increase nuclear arms.

The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes —@realDonaldTrump

"Make no mistake, this has been a difficult year," said Rachel Bronson, executive director and publisher of the Bulletin said at the press conference.

"The clock statement … makes clear, that over the the course of 2016, the global security landscape darkened, as the international community failed to come to grips with humanity's most pressing existential threat: nuclear weapons and climate change."

In particular, Bronson noted that there has been "cavalier and reckless language used across the globe, especially in the United States ... around nuclear weapons and nuclear threats."

She also said that there has been a "growing disregard" for scientific expertise that is needed for dealing with climate change effects.

A history of some of the changes to the Doomsday Clock. (CBC News)

"Climate change should not be a partisan issue," said David Titley, professor of practice in meteorology and a professor of international affairs at the Pennsylvania State University. "The planet will continue to warm to ultimately dangerous levels so long as carbon dioxide continues to be pumped into the atmosphere, irrespective of political leadership."

Titley called on the Trump administration to accept climate change as a reality.

"No problem can be solved unless its existence is first recognized," he said. "There are no alternative facts here."

In 2015, the clock moved to three minutes to midnight, ahead from five minutes set in 2012. The clock remained at three minutes to midnight in 2016.

In 1953, as a result of the first detonation of a thermonuclear bomb by the U.S. and the test of a hydrogen bomb by the Soviet Union, the clock moved to two minutes to midnight, the closest it has ever been.

Since its inception, the clock has moved ahead only 19 times.

Other concerns the scientists noted were technological, such as biotechnology and advancements in artificial intelligence.