The top five nuclear nightmares we faced in 2017 will continue to haunt us in 2018. In fact, each has gotten worse this year.

It is not that the past year has been devoid of good news, but the bad outweighed the good.

The overall number of nuclear weapons in the world continues to shrink, thanks to arms control treaties negotiated over the past few decades. The steady defeat of ISIS has reduced the risk of nuclear terrorism. Tensions seem to have eased between India and Pakistan, reducing the risk of war in South Asia.

Most promisingly, 122 nations approved a treaty banning nuclear weapons at the United Nations. The citizens group that encouraged this process, the International Campaign to Abolish Nuclear Weapons, or ICAN, won the Nobel Peace Prize for their efforts. None of the nuclear-armed states have yet joined the treaty, but as the Norwegian Nobel Committee said, “This year's Peace Prize is therefore also a call upon these states to initiate serious negotiations with a view to the gradual, balanced and carefully monitored elimination of the almost 15,000 nuclear weapons in the world.”

Yet, former chairman of the Joint Chiefs of Staff, Adm. Mike Mullen, says the risk of nuclear war is rising: "I think it's more probable than it used to be. And it scares me to death, quite frankly. They're the most dangerous weapons in the world."

Here are the top five threats, from bad to worst.

5. The new nuclear arms race. Every nuclear-armed country in the world is building new nuclear weapons. Some — China, India, Pakistan and North Korea — are adding to their arsenals. The others — France, Israel, Russia, the United Kingdom and the U.S. — are building new generations of bombers, submarines, and missiles to replace their existing Cold War weapons rather than retire them gracefully. The U.S. programs alone will cost at least $1.7 trillion over the next thirty years.

Russia and the United States hold about 95 percent of all the world’s nuclear weapons. If America were to use all the weapons in its stockpile, it could drop a hydrogen bomb on every city in the world with a population over 100,000, destroying most human and animal life on the planet. Scientists calculate that even as few as 100 weapons used in a South Asian war could trigger a nuclear winter, devastating food crops and causing a famine that could kill one billion people.

That is still not enough for some. The U.S. Congress voted this year to increase military spending and build new nuclear weapons that would smash arms control treaties because, as Sen. Tom Cotton, R-Ak., said “it's better to win an arms race than lose a war.”

4. New “usable” nuclear weapons. Several nations are building smaller, so-called “more usable” nuclear weapons. This blurs the fire-break between conventional and nuclear war. Nuclear weapons have assumed a greater role in Russia’s deterrence doctrine. They now plan to use a nuclear weapon first in a conventional conflict in Europe to “de-escalate” the war by demonstrating how serious they are.

Pakistan, similarly, is introducing growing numbers of “battlefield” nuclear weapons into its force. Just as NATO once thought it would need nuclear weapons to defeat invading Soviet tank armies, Pakistan believes it must use short-range nuclear weapons to stop an Indian invasion. India has promised to answer in kind.

The United States, too, has several new programs for weapons that would be used first in combat. In addition to a new ground-launched cruise missile the Trump administration wants the option to use in a nuclear war in Europe, the Air Force is making the first nuclear “smart” bomb, adding a tail-kit to the B-61 bomb to guide it to the ground. The greater precision, they say, will allow for a small hydrogen bomb warhead, and encourage commanders to use the weapon against conventional targets.

Michael Krepon of the Stimson Center warns, “The point of deterrence is to have no mushroom clouds, not new, tailor-made mushroom clouds for escalation control and battle management.”

Nuclear experts Phil Coyle and James McKeon add, “The use of just one small nuclear weapon would almost certainly trigger a like-for-like retaliation, followed by a similar or stronger response from the original aggressor and progression toward a nuclear apocalypse. The assumption that crossing the nuclear threshold can lead to anything other than colossal destruction puts hundreds of millions of lives at risk.”

Indeed, the U.S. nuclear command in November wargamed scenarios to see if two militaries that possessed nuclear weapons could even resist using them and stick to fighting a conventional war. “It’s dicey. It’s dicey and that’s one place we don’t want to go,” said Brig. Gen. Gregory Brown, the J3 deputy director for global operations at U.S. Strategic Command, at November’s Defense One Summit, in Washington. “When one side begins to use them, then the temptation to utilize those weapons… the Russians escalate to win, not to de-escalate. So it gets to a very difficult calculus and it’s clearly a place that we don’t want to go.”

3. Destruction of the Iran Deal. UN Amb. Nikki Haley’s December 14 speech on Iran was ominous. Carefully selecting intelligence to portray Iran as the source of instability in the Middle East, she was eerily reminiscent of speeches about Iraq in the buildup to war. It appears part of an orchestrated effort to make the case for withdrawing from the 2015 nuclear accord that rolled back and froze Iran’s nuclear program.

President Donald Trump again will have to certify in mid-January that Iran is complying with the agreement (as U.S. intelligence agencies and the International Atomic Energy Agency repeatedly report they are) and waive sanctions lifted by the deal. If, as appears likely, he fails to do this, the deal could collapse, ending all limits and inspections now imposed on Iran. With restrictions gone and new sanctions impossible, the only alternative to preventing the rebuilding of Iran’s nuclear program will suddenly become military action.

Sen. Dianne Feinstein, D-Calif., warns, “Having voluntarily walked away from an agreement for no reason, it is difficult to imagine the president would be able to lead the international community in pressuring Iran back to the negotiating table.” Former Iran deal negotiator Amb. Wendy Sherman agrees: “If President Trump undermines the nuclear deal, the repercussions for American foreign policy will be disastrous: It will drive a wedge between the United States and Europe, weakening the critical trans-Atlantic relationship and increasing the influence of Iran, Russia and China.” She adds, “This information vacuum could, in short order, lead us to consider military action to destroy Iranian nuclear facilities, perhaps leading to a wider war in the Middle East.”

2. War with North Korea. Although U.S. military planners have long designed their forces to fight in two theaters at the same time, they never imagined that it could be two wars started by choice. But there is a growing chorus in Washington for a military strike on North Korea. “The Trump national security team seems convinced that North Korea cannot be deterred, and war is the inevitable outcome,” concludes Tufts University professor Daniel Drezner. Former CIA Director John Brennan last month estimated the chance of a war at 20 to 25 percent. Council of Foreign Relations President Richard Haass puts the odds at 50-50.

Secretary of State Rex Tillerson’s ray of hope in a December 13 talk that the administration was finally willing to “sit down and see each other face to face” was quickly extinguished by the White House, which once again said it would only talk if North Korea agreed to eliminate all its nuclear weapons. The administration’s policy increases the drift towards war, with unimaginable consequences.

Hundreds of thousands of South Koreans and Americans stationed there could die within the first few hours of a conventional war. If there is a nuclear exchange, “there easily could be a million deaths on the first day,” says Stanford University scholar Scott Sagan.

1. An Impulsive Finger on the Button. The greatest nuclear danger does not come from a foreign threat or a terrorist group but from our own president. The Washington Post, reporting on how intelligence briefings are shaped so as not to upset President Trump, concludes that “the personal insecurities of the president have impaired the government’s response to a national security threat.” Many fear that the president’s mental condition is itself a national security threat. This is, like so much of the past year, unprecedented.

Concern over the president’s mental stability and his sole, unchecked authority to launch nuclear weapons caused the Senate Foreign Relations Committee this year to hold the first hearings on nuclear command and control in over 40 years. Chairman Bob Corker, R-Tenn., fearing that Trump was leading the nation “on the path to World War III,” convened the hearing. Sen. Chris Murphy, D-Conn., voiced his deep fear at the session: “We are concerned that the president of the United States is so unstable, is so volatile, has a decision-making process that is so quixotic that he might order a nuclear weapons strike that is wildly out of step with U.S. national security interests.”

Once an order is given, no one could stop it. Mullen, when asked if a general could refuse Trump’s order, said, “Any senior military officer always approaches it from the standpoint of we're not going to follow an illegal order. That said, the president is in a position to give a legal order to use those weapons. And the likelihood that given that order that it would be carried out I think would be pretty high."

Most experts agree. Former Director of National Intelligence James Clapper worries that if Trump, “in a fit of pique” decides to launch a nuclear strike, “there’s actually very little to stop him. The whole system is built to ensure rapid response if necessary. So there’s very little in the way of controls over exercising a nuclear option, which is pretty damn scary.” Senators and House Members have introduced legislation to change the decision process and policy.

The fear of a mad, nuclear-armed president haunts those outside the United States as well. “While the global community may trust that no responsible head of state would ever order another nuclear attack, we have no guarantees that it will not happen,” Berit Reiss-Andersen, head of the Norwegian Nobel Committee, warned during the prize ceremony this month. “Despite international legal commitments, irresponsible leaders can come to power in any nuclear-armed state and become embroiled in serious military conflicts that veer out of control.”

Nobel Laureate Beatrice Fihn was more direct: “The only rational course of action is to cease living under the conditions where our mutual destruction is only one impulsive tantrum away.”

To paraphrase Walt Kelly’s famous comic strip character, Pogo, we have met the world’s worst nuclear threat, and it is us.