The symbolic "Doomsday Clock" moved two minutes closer to midnight this week, and this time the Bomb was only part of the reason.

The world's failure to reduce carbon emissions, which is driving global climate change, along with modernization of the world's nuclear arsenals, drove the Bulletin of the Atomic Scientists to set its symbolic timepiece at three minutes to midnight — the closest setting since the depths of the Cold War.

"World leaders have failed to act with the speed or on the scale required to protect citizens from potential catastrophe," said Kenette Benedict, the journal's publisher. The situation isn't hopeless, but citizens must demand action to cut carbon "soon — very soon" to prevent disaster.

"In sum, stunning governmental failures have imperiled civilization on a global scale," Benedict said.

The Bulletin created the clock in 1947 as a way of highlighting the risks of the nuclear age. It began factoring in climate change as "a dire challenge to humanity" in 2007.

UN members are set to gather in Paris in December to hammer out a plan to reduce emissions in hopes of limiting climate change to two degrees Celsius (1.8 degrees Fahrenheit) above pre-industrial levels. The world body called on countries to begin submitting their plans this week via a new website; those plans should include timetables for cutting carbon output in "clear and transparent documents."

Richard Somerville, a member of the Bulletin's Science and Security Board, said the steps taken to reduce carbon emissions to date are "entirely insufficient" to head off disaster.

"Unless much greater emissions reductions occur very soon, the countries of the world will have emitted enough carbon dioxide and other greenhouse gases by the end of this century to profoundly transform the Earth's climate," he said. "The resulting climate change will harm millions of people and will threaten many key ecological systems on which civilization relies."

Scientists say warming temperatures are likely to result in higher sea levels, more acidic oceans, and more intense storms and droughts, with consequences that are expected to fall disproportionately on the world's poor. Previous climate talks have been hamstrung by disputes between the industrialized West and rapidly developing countries like India and China, which are building new fossil-fueled power plants at a rapid clip.

The world's two largest emitters, China and the United States, reached a landmark agreement on reducing carbon output in November. But US opponents of reducing emissions continue to insist that the science is still in doubt despite a decades-long warming trend.

While many supporters of tough climate action have called for more nuclear power plants to replace carbon-intensive coal stations, building more reactors risks the spread of technology that could be used to produce a nuclear bomb, Benedict said.

"The international community has not developed coordinated plans to meet the challenges that nuclear power faces in terms of cost, safety, radioactive waste management, and proliferation risk," she said.

Meanwhile, about 16,300 nukes remain in the world's declared stockpiles, and the post-Cold War process of drawing down those arsenals "has ground to a halt," Benedict said. India, Pakistan, and North Korea have joined the list of declared nuclear powers since 1991, and the biggest — the United States and Russia — are upgrading their remaining warheads.

The clock has been set at three minutes to midnight twice before: In 1949, when the Soviet Union conducted its first nuclear tests; and in 1984, when dialogue between Washington and Moscow ground to a near halt.

The closest it's been was in 1953, when US and Soviet development of the hydrogen bomb drove the journal to move the hands to two minutes to midnight. In 1991, with the Cold War over and the superpowers standing down from decades of hair-trigger alert, the clock was moved back to 17 minutes away.