Future historians, if there are any, will be dumbfounded. Today, uncountable dollars and unquantifiable hysteria are devoted to the distant threat of climate change milder than some changes Earth has experienced. A recent peer-reviewed study of scientific estimates concludes that the average annual cost of what the excitable UN secretary general calls “global boiling” might reach 2 percent of global gross domestic product by 2100. Meanwhile, negligible public anxiety accompanies the intensifying danger of global incineration from nuclear war.

High anxiety is unsustainable, but in a presidential election year it can temporarily concentrate minds. Reading “Nuclear War: A Scenario” by reporter and historian Annie Jacobsen will take you much longer than the 30 or so minutes—1,800 seconds—that would elapse between the launch of a single nuclear-armed intercontinental ballistic missile in North Korea and its detonation on the Pentagon. Thereafter, in Jacobsen’s scenario, cascading and irreversible events extinguish civilization in two hours.

A few tenths of a second after the launch, a bus-size U.S. satellite 22,300 miles above Earth detects the missile’s plume. Six seconds later, computers in the command center beneath the Pentagon are predicting its destination: the Pentagon. Twenty-four seconds later, at the military’s Cheyenne Mountain Complex in Colorado, computers generate this message: “NUCLEAR LAUNCH ALERT.”

Jacobsen’s most chilling point: “The speed at which nuclear war will unfold, and then escalate, all but guarantees that it will end” in civilizational collapse. One of her sources, former defense secretary William J. Perry, says: “Many presidents come to the office uninformed about their role in a nuclear war. Some seem not to want to know.” They should know that the “launch on warning” policy could force them to go to nuclear war in the minutes required to brew a cup of coffee.

The traditional goal in battle, Jacobsen writes, “is to meet attacking sword with defensive shield.” The total number of U.S. interceptor missiles: 44. Attacked, would the United States “retaliate to decapitate” the attacking regime? A problem: U.S. Minuteman III ICBMs do not have enough range to hit North Korea without over-flying Russia. In Jacobsen’s scenario, Russia reacts violently.

Everything—everything—depends on deterrence holding, forever. It succeeded in keeping the U.S.-Soviet conflict from becoming hot during the Cold War. But conventional forces failed to deter Vladimir Putin’s invasion of Ukraine. And he—possessing the world’s largest arsenal of nuclear weapons and perhaps the world’s smallest reluctance to use them—has used nuclear deterrence to dissuade Ukraine’s allies from delivering sufficient timely assistance. Otherwise, U.S. and European Union resources could by now have saved Ukraine. But then, a non-nuclear Russia might not have risked an invasion.

Jacobsen says that in 1983, President Ronald Reagan ordered a simulated war game to explore the probable dynamics of a nuclear attack and counterattack: “Over the course of two weeks, in every simulated scenario—and despite whatever particularly triggering event started the war game—nuclear war always ended the same way.” A minimum of half a billion dead after the first salvos. “There is,” Jacobsen insists, “no such thing as de-escalation.”

Jacobsen vividly imagines the horrors of unconstrained nuclear onslaughts: metal-melting heat, beyond-hurricane-level winds, radiation poisoning, the end of agriculture, social disintegration because of electric Armageddon (the electric grid vanishes, and with it the nation’s communications and financial infrastructure) and ecological collapse: Swarms of disease-bearing mosquitoes, the birds that preyed on them being dead, feast on sewage, garbage and the dead.

Jacobsen cannot be faulted for not proposing “solutions” to the dilemma of living with what physics hath wrought. Her point is that for a while now, and from now on, humanity’s survival depends on statesmanship and luck—as much the latter as the former. Remember that on Nov. 5.

The second use of nuclear weapons occurred three days after the first. There has not been a third use for almost 28,800 days. Talk of “banning the bomb” is pointless. These weapons are here forever. Or so we must hope: They will exist until they are used. But as long as they are not used, the words of Gen. C. Robert Kehler, former head of the U.S. Strategic Command, will be true every hour of every day: “The world could end in the next couple of hours.”