Even as Republicans on Capitol Hill voted repeatedly this week to deny climate science, the Nobel Laureates with the Bulletin of Atomic Scientists declared that world leaders’ failure to slow climate change poses “extraordinary and undeniable threats to the continued existence of humanity.” What’s more, a renewed nuclear arms race has left US and Russian nuclear arsenals poised on fifteen-minute alert to unleash roughly 1,600 total warheads against one another. Combined, the climate and nuclear dangers mean that “the probability of global catastrophe is very high, and the actions needed to reduce the risks of disaster must be taken very soon.”

Not since the depths of the Cold War, in 1984, has the Clock been moved so close to the apocalyptic midnight demarcation. Only once in the Clock’s sixty-eight-year history has its threat level been higher—in 1953, following the US’s first explosion of a hydrogen bomb, when it was set at two minutes to midnight.

Since its creation in 1947 by scientists who had helped develop the atomic bomb, the Doomsday Clock has become an internationally recognized indicator of humanity’s vulnerability to nuclear destruction. The scientists who advise the Bulletin’s annual evaluation of the Clock, which currently include seventeen Nobel Prize winners, sometimes offer encouraging news. For example, the Clock was moved back to twelve minutes before midnight in 1972 after the United States and the Soviet Union signed the Anti-Ballistic Missiles and the Strategic Arms Limitations treaties, and to seventeen minutes before midnight in 1991 after the superpowers began making large cuts in their arsenals following the signing of the Strategic Arms Reduction Treaty. Climate change was added to the Bulletin’s calculations in the 2000’s amid growing signs that rising greenhouse gas emissions threatened similarly widespread, if less immediate, damages as nuclear war did.

“We were happy to see the emergence of a grassroots climate movement in 2014 with the huge climate march in New York, but the question is how much time do we have,” Kennette Benedict, the executive director of the Bulletin, told The Nation. “Our scientists say that it’s getting very late in the game. And we don’t see much political leadership, especially in Congress, and they will have to be in on this to make it work.”

Indeed, the Republican-controlled Senate spent much of the week trying to pass a bill to force the construction of the Keystone XL pipeline—a bill President Obama has vowed to veto—while simultaneously denying that human activities are the main driver of climate change. Democrats tried in vain to attach to the Republicans’ Keystone bill various amendments affirming climate science. Senator Bernie Sanders, an independent from Vermont, sponsored an amendment saying that climate change is real, human-caused and already creating devastating problems in the US and around the world and therefore the United States must transform its energy system away from fossil fuels to energy efficiency and renewable energy sources. The amendment was defeated 56-42, with zero Republican Senators daring to support it.

One such devastating climate problem is the “irreversible” melting of part of the West Antarctic ice sheet, which scientists announced last May. The melting cannot be stopped largely because of the physical momentum of global warming—the fact that carbon dioxide, once emitted, remains in the atmosphere for hundreds of years. “That means that many island nations will be gone,” Benedict said. “Much of Bangladesh, and other low-lying regions, the same. It’s only a matter of time.”

Meanwhile, “just because the threat of nuclear war has been forgotten doesn’t mean it went away,” Eric Schlosser told The Nation. Schlosser’s book, Command and Control, revealed that at least 1,200 US nuclear weapons were involved in significant accidents between 1950 and 1968, including one incident when a single safety switch prevented a detonation in North Carolina that could have devastated Washington, DC. Schlosser added, “The odds of a major city, somewhere in the world, being destroyed by a nuclear weapon are probably greater today than ever before. Unlike global warming, that sort of catastrophe will occur instantaneously and won’t be reversible.”

Notwithstanding the progress made in the immediate aftermath of the Cold War, today Russia and the United States are “pretty much on a ‘launch on warning’ posture,” said Benedict, even as the Ukraine conflict and other tensions have increased distrust on both sides. Obama and Russian president Vladimir Putin each have about fifteen minutes after being warned of a potential nuclear attack in which to halt an otherwise automatic response from all three legs of the nuclear weapons triad—bombers, submarines and ground-based missiles—that would unleash approximately 800 warheads against the adversary. “So if there is an accident or a miscommunication—and there have been more than a few in the past—and it isn’t caught in time, the result would be unthinkable,” Benedict concluded.

Although unwilling to sugarcoat the facts, the Bulletin scientists do repeatedly emphasize that “we can and must turn this around.” Methods and machines exist to enable humanity to leave fossil fuels behind in favor of renewable energy sources, and to do so at moderate economic cost. National security can be achieved while shrinking and stabilizing nuclear arsenals. The obstacles are not technological but political. The true need, then, the scientists assert, is for “the citizens of the world to demand action from their leaders.”