An excerpt from The Doomsday Machine, which was published this month by Bloomsbury. The book is an account of America’s nuclear program in the 1960s drawn from Ellsberg’s experience as a consultant to the Department of Defense and the White House, drafting Secretary Robert McNamara’s plans for nuclear war. Ellsberg is the author of Secrets, a book about his experiences leaking the Pentagon Papers.

From The Doomsday Machine, which was published this month by Bloomsbury. The book is an account of America’s nuclear program in the 1960s drawn from Ellsberg’s experience as a consultant to the Department of Defense and the White House, drafting Secretary Robert McNamara’s plans for nuclear war. Ellsberg is the author of Secrets, a book about his experiences leaking the Pentagon Papers.

At the conclusion of his 1964 film, Dr. Strangelove, Stanley Kubrick introduced the concept of a “Doomsday Machine”—designed by the Soviet Union to deter nuclear attack against the country by automating the destruction of all human life as a response to such an attack. The movie’s Russian leader had installed the system before revealing it to the world, however, and it was now being triggered by a single nuclear explosion from an American B-52 sent off by a rogue commander without presidential authorization.

Kubrick had borrowed the name and the concept of the Doomsday machine from my former colleague Herman Kahn, a Rand physicist with whom he had discussed it. In his 1960 book On Thermonuclear War, Kahn wrote that he would be able to design such a device. It could be produced within ten years and would be relatively cheap—since it could be placed in one’s own country or in the ocean. It would not depend on sending warheads halfway around the world.

But, he said, the machine was obviously undesirable. It would be too difficult to control— too inflexible and automatic—and its failure “kills too many people”—everyone, in fact, an outcome that the philosopher John Somerville later termed “omnicide.” Kahn was sure in 1961 that no such system had been built, nor would it be, by either the United States or the Soviet Union.

The physicist Edward Teller, known as the “father of the H-bomb,” likewise denied that omnicide—a concept he derided—was remotely feasible. In answer to a question I posed to him in 1982, he said emphatically that it was impossible that the thermonuclear weapons that he had co-invented would kill “more than a quarter of the earth’s population.”

At the time, I thought of this assurance, ironically, as a version of the glass being three quarters full. (Teller was, along with Kahn, Henry Kissinger, and the former Nazi missile designer Wernher von Braun, one of Kubrick’s inspirations for the character of Dr. Strangelove.) And Teller’s estimate was closely in line with what the Joints Chief of Staff, or JCS, actually planned to do in 1961, though a better estimate would have been closer to one-third to one-half of the world population.

But the JCS were mistaken in 1961, and so was Herman Kahn in 1960, and so was Teller in 1982. Just one year after Teller had underestimated the destructive powers of nuclear weapons, the first papers to describe the phenomenon of nuclear winter were published. Nuclear winter referred to the effects of smoke injected into the stratosphere by firestorms generated by H-bombs. Although the Doomsday machine wasn’t likely to kill every last human, its fallout, once triggered, would come close to deserve its name.

Like covert operations and assassination plots, nuclear war plans and threats are not publicly discussed by the small minority of officials and consultants who know anything about them. These officials keep silent to maintain high clearances, access, and the possibility of being consultants after they’ve left service. This discretion, coupled with systematic secrecy, lying, and obfuscation has created extremely deficient scholarly and journalistic understanding and almost total public and congressional ignorance.

As a result, most aspects of the US nuclear planning system that I knew half a century ago still exist today, as prone to catastrophe as ever but on a scale that vastly exceeds what was understood then. The present risks of the current nuclear era go far beyond the dangers of proliferation and non-state terrorism that have been the almost exclusive focus of public concern for the past generation and the past decade in particular. The arsenals and plans of Russia and the US are not only an insuperable obstacle to an effective global anti-proliferation campaign; they are themselves an existential danger to the human species.

The hidden reality I aim to expose is that for more than fifty years, all-out thermonuclear war—an irreversible, unprecedented, and almost unimaginable calamity for civilization and most life on earth—has been, like the disasters of Chernobyl, Katrina, the Gulf oil spill, and Fukushima Daiichi, and a catastrophe waiting to happen, on a scale infnitely greater than any of these. And that is still true today.

Here is what we now know: the United States and Russia each have an actual Doomsday Machine. It is not the same system that Herman Kahn envisioned (or Stanley Kubrick portrayed), with warheads buried deep and programmed to explode in their own territories, producing deadly global fallout. But a counterpart nevertheless exists for both countries: a system of men, machines, electronics, communications, institutions, plans, training, discipline, practices, and doctrine—which, under conditions of electronic warning, external conflict, or expectations of attack, would with unknowable but possibly high probability bring about the global destruction of civilization. These two systems still risk doomsday: both are on hair-trigger alert that makes their joint existence unstable. This is true even though the Cold War that rationalized their existence ended thirty years ago.

Here’s the scenario: the fallout would remain mostly limited to the northern hemisphere but the smoke and soot genereated by fierce firestorms in hundreds of burning cities would be lofted into the stratosphere, where it would not rain out and would remain for a decade or more, enveloping the globe in smoke and blocking out sunlight, lowering temperatures to the level of the last Ice Age, and killing all harvests worldwide, causing near-universal starvation within a year or two.

U.S. plans for thermonuclear war in the early sixties, if carried out in the Berlin or Cuban missile crises, would have killed many times more than the six hundred million people predicted by the JCS. They would have starved to death nearly everyone then living: at that time three billion people. The numbers of warheads in the possession of the U.S. and Russia have since declined. Yet according to the most recent scientific calculations, even a fraction of the existing arsenals would be enough to cause nuclear winter today.

Does the United States still need a Doomsday Machine? Does Russia? Did they ever? Does its existence serve any national or international interest to a degree that would justify the danger to human life?

I do not ask the questions rhetorically. They deserve sober, reflective consideration. The answers seem obvious, but as far as I know they have never been addressed. There follows another question: Does any nation on earth have a right to possess such a power? A right to threaten—by its simple possession of that power— the continued existence of all other nations and their people, their cities, and civilization as a whole? Why is anything other than zero risk remotely acceptable?

We did not set out intentionally to acquire a doomsday capability. The existence of one such machine does not create a tangible incentive for an enemy to have one. In fact, having two on alert against one another is far more dangerous than if only one existed. If the two existing machines were stripped of their doomsday potential, there would be no strategic rationale to reconstruct it, any more than there was a conscious intention in the first place.

The good news is that dismantling the Doomsday Machine in one country or both would be relatively simple in concept and in physical operation (though politically and bureaucratically incredibly difficult). It could be accomplished within a year. But it would mean—and here’s where institutional resistance would be strong—giving up certain illusions about our nuclear forces. It would mean scrapping our strategic nuclear war plans and discarding most of the forces deployed to carry them out.

However low the probability might currently be of the United States or Russia carrying out its strategic contingency plans against the other and causing nuclear winter, it never will be zero, so long as Doomsday Machines of the present type exist. Just how high does the risk have to be to make it intolerable? What risk of nuclear winter is “acceptable” as the price of maintaining our current strategic forces?

Since the end of the Cold War, the greatest likelihood is that a preemptive atttack will be triggered by an electronic false alarm (which has repeatedly occurred) or an accidental detonation (which was a real risk in a number of previous accidents).

The danger that either a false alarm or a terrorist attack on Washington or Moscow would lead to a preemptive attack derives almost entirely from the existence in both countries of land-based missile forces, each vulnerable to attack by the other and therefore kept on a high state of alert, ready to launch within minutes of warning.

The easiest and fastest way to reduce that risk—and indeed, the overall danger of nuclear war—is to dismantle entirely (not merely “dealert”) the Minuteman III missile force, the U.S. land-based leg of the nuclear “triad.” This shift would not totally eliminate the dangers of nuclear war, but it would abolish the threat of nuclear winter.

This dismantlement of the Doomsday Machines is not intended as an adequate longterm substitute for more ambitious, necessary goals, including total universal abolition of nuclear weapons. We cannot accept the conclusion that abolition must be ruled out “for the foreseeable future” or put off for generations. There will not be a human future without it.

The nuclear weapon states must acknowledge the reality that they have been denying and that non-nuclear weapon states have been proclaiming for almost fifty years: effective nonproliferation is unavoidably linked to nuclear disarmament. Either all nations forgo the right to possess nuclear weapons indefinitely and to threaten others with them under any circumstances, or every nation will claim that right, and actual possession and use will become widespread.

What is often missing in the typical discussion of nuclear policies is the recognition that what is being discussed is dizzyingly insane. It is insane in its almost-incalculable destructiveness and deliberate murderousness, its disproportionality of risked and planned destructiveness for its secretly pursued aims (damage limitation to the United States and allies, “victory” in two-sided nuclear war), its criminality (to a degree that explodes visions of law, justice, crime), its lack of wisdom or compassion, its sinfulness and evil.

And yet part of what must be grasped—what makes it both understandable, once grasped, and at the same time mysterious and resistant to our ordinary understanding—is that the creation, maintenance, and political use of these monstrous machines has been directed and accomplished by ordinary people, neither better nor worse than the rest of us.

Is it really possible that normal, ordinary politicians, analysts, and military strategists have created and accepted dangers of the sort I am describing? Every impulse is to say “No! It can’t be that bad! And if it ever was, it can’t be true now, in our own country.”

That impulse is mistaken. After all, we Americans have seen human-caused catastrophes in recent years reflecting governmental or corporate recklessness that is far more conscious and deliberate. Above all, the invasion of Iraq and the occupation of Afghanistan, but also the failure to prepare for or respond to Hurricane Katrina, the Gulf oil spill, and the 2008 financial crisis: the savings-and-loan scandal, Internet and housing bubbles, criminal fraud, and the meltdown of the banking and investment system.

Perhaps reflection on these political, social, and moral failures—and the disastrous decision- making of Donald Trump—will lend credibility to my basic theme, otherwise hard to absorb: that these same heedless, shortsighted, reckless, and dishonest decisions have characterized our government’s nuclear policies, risking a catastrophe incomparably greater than all others.

Our mortal predicament did not begin with the election of Donald J. Trump, and it will not end with his departure. The obstacles to achieving these necessary changes are posed not so much by the American public—though in recent years it has shown dismaying manipulability— but by officials and elites in both parties and by major institutions that consciously support militarism, American hegemony, and arms production and sales.

No policies in human history have more deserved to be recognized as immoral. The story of how this calamitous predicament came about and how and why it has persisted for over half a century is a chronicle of human madness. Whether Americans, Russians, and the rest of the world can rise to the challenge of reversing these policies and eliminating the danger of near-term extinction caused by their own inventions and proclivities remains to be seen. I choose to act as if that is still possible.