These include the jaw-droppingly cavalier approach taken by Manhattan Project scientists who theorised a risk of as much as 10 per cent that the atomic bomb would set the skies and seas alight. And yet they proceeded with the Trinity test in July 1945 when World War II was all but won.
We're told too, how the US had preplanned targets that would destroy every city in the Soviet Union and China in the advent of a nuclear war with Russia.
The policy lasted until at least 1968, even though the Sino-Soviet split between the two former communist allies was by then almost a decade old, Ellsberg tells Fairfax Media. Such a general nuclear war would kill 600 million people – mostly in the Warsaw Pact nations and China, but also more than 100 million in western European nations allied to the US – Ellsberg managed to glean from a senior White House official working for US president John F. Kennedy.
Ellsberg, who turns 87 next month, credits the emergence of Donald Trump for rekindling interest in nuclear issues. The release of the Hollywood blockbuster The Post – dramatising how his Vietnam War disclosures helped transform The Washington Post newspaper – has also bolstered interest in his book (which was turned down by 17 publishers before Bloomsbury took it up).
Despite his portrayal in the film, Ellsberg was far more than a marine grunt [an officer, in fact]. Rather, he had served as a highly regarded consultant with RAND Corp with "go anywhere, ask anything, see anything" clearance.
Such access included a near front-row seat to the 1962 Cuban Missile Crisis that brought the world to the brink of nuclear annihilation.
In fact, Ellsberg once had documents too – some 8000 pages he'd secretly copied – on those years. That stash had been more than the 7000-page Vietnam War study he'd managed to make public in 1971.
His original plan was to release the Pentagon Papers as a "tactical" move to deal with the immediate issue of "where the bombs are falling right now", Ellsberg reveals in the new book.
He separated the mostly nuclear documents from the Vietnam story, giving the former to his brother, Harry, for safe-keeping in his home in Westchester County, New York. Fearing their discovery at the time newspapers were running the Vietnam leaks, Harry moved the hoard – inside a garbage bag within a cardboard box – from under a compost heap to a nearby urban dump just a day before plain-clothed men swooped on his garden.
The fall-back plan, though, didn't anticipate a near-hurricane strength storm which collapsed the bluff where the documents were buried into a larger landfill below. Months of weekend digging, even with a backhoe, failed to find them.
"I didn’t say I had copied documents because I had lost them, unfortunately, so I didn’t draw attention to the fact," Ellsberg tells Fairfax Media.
Still, enough material has surfaced since to allow Ellsberg to detail the complex "Doomsday" arrangements – and the Soviet "dead hand" equivalent – that have keep the world much closer to nuclear devastation than most people realise over the past six decades.
"A large amount, probably more than half, has been confirmed" he says, such as from freedom of information efforts and releases by the National Security Archive. "Of course what has not come out are my own notes and my own feelings about it exactly."
Ellsberg remains frustrated that more people aren't aware of the close calls.
These include the October 1960 false alarm given by a new radar complex in Thule Air Base on Greenland that declared a 99.9 per cent certainty of Soviet missiles heading towards the US, only to learn later that the system was picking up signals bouncing off the moon as it rose over Norway. (Operators discounted the threat because Soviet leader Nikita Khruschev was in New York to attend a United Nations gathering at the time.)
"I testified under oath [about the nuclear risks] and it wasn’t even mentioned in the newspaper accounts, including a lot of what’s in this book," he says. "The 600 million dead, stuff like that, pretty dramatic, but nobody ever paid much attention to it because I didn’t have a document to back it up."
Also overlooked, to Ellsberg's frustration, are two chapters in his new book devoted to the original Doomsday quandary – that an atomic bomb could trigger the ignition of nitrogen in the atmosphere and hydrogen in the oceans.
"The earth would blaze for less than a second in the heavens and then forever continue its rounds as a barren rock," Ellsberg writes, describing a debate on the second day of the first meeting of the scientists who would anchor the Manhattan Project in July 1942.
The boffins calculated the risk of a doomsday event resulting from detonating the atomic bomb at three in a million. However, one physicist Enrico Fermi – whom Ellsberg labels, "the most brilliant of the experimental scientists among them" – rated it a 10 per cent chance.
Obviously, the New Mexico bomb test three years later didn't destroy life on Earth – nor the bombings of Hiroshima and Nagasaki and all the subsequent tests of more powerful hydrogen bombs.
Accounts of the countdown to the Trinity test, though, suggest more than a few scientists had fingers crossed that their blackboard scribblings were accurate. [A runaway chain reaction is impossible – though scientists didn't settle on that until later.]
Ellsberg says he included those chapters to highlight human risk-taking. While a German fissile bomb was a possibility in 1942, it wasn't by mid-1945, and the dozens of Japanese cities being firebombed one by one meant that country's defeat was inevitable, he says.
“First, [it shows] that intellect of the highest order – literally, the highest order, in terms of IQ, genius and brilliance – is not a sure protection against extreme recklessness and unwise decision-making," Ellsberg tells Fairfax Media.
"It poses the question about rationality in general among humans, and I don’t perceive that this risk-taking capability is confined to the most brilliant people by any means.”
Ellsberg was in high school during the Manhattan Project years, and his account relies on what he learned at RAND, his later research and some personal encounters.
But he got to experience up-close an actual risk of Armageddon during the Cuban Missile Crisis. US secretary of defence Robert McNamara would later reveal his musings one evening about never seeing another sunset.
"Paul Nitze, almost the founder of the Cold War … and my boss during the Cuban Missile Crisis, had estimated the risk of all-out nuclear war at at least 10 per cent," Ellsberg tells Fairfax Media.
Later revelations about the compounding threats during the crisis suggest 10 per cent might be conservative.
Incidents included a Russian submarine preparing to launch its "special weapon" as the US Navy dropped depth-charges above, the underestimation of the number of Soviet troops already on Cuba in the case of a US invasion, and the straying of a U2 spy plane into Russian airspace.
Advances in other fields have also cast more insights into the perils facing a planet where nine nations now have declared nuclear weapons.
(US and Russia have scaled back their arsenals from a peak of more than 63,000 weapons between them in 1986, but they continue to account for 93 per cent of the world's 14,900 known nuclear weapon stockpile, according to the Ploughshares Fund.)
These knowledge gains include climate science where a better understanding of atmospheric circulation led researchers to warn by 1983 of a nuclear winter should a full-scale nuclear exchange take place. While rains would wash out radiation, enough of the smoke from burning cities would reach the stratosphere, blocking enough sunlight to throw the whole planet into a deep chill. Survivors would likely struggle to make it through the subsequent mass starvations.
Perhaps not coincidently – as other researchers such as Naomi Oreskes and Erik Conway note in their book, Merchants of Doubt – the nuclear weapons industry ended up spawning some of the early and most vehement deniers of climate change.
These included Robert Jastrow, Frederick Seitz and Edward Teller, the "father of the hydrogen bomb".
"They also tend to be quite libertarian, opposing regulation in general," Ellsberg says.
"Climate is one of those things you cannot deal with on a national basis or a private-enterprise basis adequately," he says. "It has to be international and it involves government regulation – so they’re against that in principle.”
Peter Hannam is Environment Editor at The Sydney Morning Herald. He covers broad environmental issues ranging from climate change to renewable energy for Fairfax Media.
Morning & Afternoon Newsletter