How does the human story end? One thing is fairly certain: our expanding universe will someday settle into an eternal state of frozen chaos—known as thermodynamic equilibrium—that will make all life impossible, although this won’t happen for an extremely long time. In the meantime, we face a plethora of risks from nature like volcanic supereruptions, asteroids, comets, gamma-ray bursts, black hole explosions, supernovae, and so on. Fortunately, these are on the whole quite improbable. The most probable scenario is a volcanic supereruption, which is estimated to occur once every 50,000 years on average, and in fact our Homo sapiens ancestors survived two such eruptions in the past. So we don’t need to worry all that much about the assassination of our species by natural phenomena.

Unfortunately, the same cannot be said about anthropogenic—or human-caused—threats. Many leading experts today put the probability of humanity pushing itself over the cliff of extinction this century unnervingly high, at perhaps 20 percent or more, and indeed Lord Martin Rees has argued that there’s a 50/50 chance of civilizational collapse before 2100, which may or may not entail our disappearance. The most currently discussed anthropogenic threat is of course climate change, the result of burning fossil fuels. According to the latest IPCC report:

Half of the world’s people are “highly vulnerable” to serious impacts from the climate crisis, a billion people in coastal areas face inundation, mass die-offs of species including trees and coral have already begun, and close to a tenth of the world’s farmland is set to become unsuitable for agriculture.

There’s no doubt that we’re on a path toward a climate catastrophe, which will fundamentally change the conditions of human life—of all life—for millennia. Consider an ominous statistic about one consequence of climate change, the loss of biodiversity: between 1970 and 2016, the global population of wild vertebrates, which includes mammals, birds, reptiles, amphibians, and fish, declined by a staggering 68 percent. Feel free to extrapolate that number into the future. Some children born today won’t have to: they’ll witness the collapse of the biosphere for themselves.¹

One threat that hasn’t been prominent on the cultural landscape since the early 1990s is nuclear war. The obvious reason is that the Cold War officially ended in 1991, thereby greatly reducing the likelihood that the U.S. and Soviet Union might exchange a flurry of nuclear missiles targeting each others’ urban centers. This was an extraordinary, hopeful moment in human history, and indeed the Doomsday Clock, which attempts to convey our collective proximity to total annihilation, leaped back from 6 minutes before midnight (doom) in 1988 to 10 minutes in 1990 and 17 minutes the following year.

But the danger has never really gone away: North Korea has conducted six nuclear tests since 2006, and in 2002, tensions between India and Pakistan—both nuclear nations—nearly culminated in a “war that both governments thought might go nuclear.” There was also a close call in 1995—after the Cold War—during which, to quote the former president of the Ploughshares Fund, Joseph Cirincione:

Russian military officials mistook a Norwegian weather rocket for a US submarine launched ballistic missile. Boris Yeltsin became the first Russian president to ever have the “nuclear suitcase” open in front of him. He had just a few minutes to decide if he should push the button that would launch a barrage of nuclear missiles. We believe his senior military officials advised him that he had to launch. Thankfully, he concluded that his radars were in error. The suitcase was closed.

This was, in fact, just one of many near misses, almost-nuclear-wars, that have occurred since 1945. Consider that in 1962, two of three officials on a Soviet submarine voted to launch a nuclear torpedo at the U.S. If it weren’t for Vasili Arkhipov, the only officer to object, this would almost certainly have triggered World War III. Or another case: few are aware that in a field around Goldsboro, NC, there lies an undetonated thermonuclear weapon that was dropped accidentally by a U.S. bomber. (No one knows where exactly; the device has never been found.) If it had exploded, the resulting chaos might very well have led the U.S. to strike the Soviet Union. Examining the list of close calls, it’s difficult not to believe that if the tape of history were rewound and played again from 1945 onward, it would probably take just one rerun for civilization to self-destruct. Most people don’t realize just how lucky we are to be alive today.

Now enter Putin, whose nuclear rhetoric has increased alarmingly over the past few weeks. On February 19, he “oversaw military manoeuvres by strategic nuclear missile forces,” and subsequently put Russia’s nuclear forces on high alert while threatening its enemies with “consequences ‘you have never seen in your history.’” Russia has the largest nuclear arsenal in the world, with 1,588 nuclear warheads currently deployed on ballistic missiles or at heavy bomber bases. And according to many experts, Putin may very well opt to use one—or many—“tactical” nukes in Ukraine as part of Russia’s “escalate to de-escalate” military policy. Some have even suggested that this scenario may be rather probable, something we should expect to happen, especially as the conflict in Ukraine drags on. “Every time you think, ‘No, he wouldn’t, would he?,’” Fiona Hill recently told Politico in a discussion of the nuclear threat, “Well, yes, he would.” Under Putin, Russian forces have already targeted a maternity hospital and children’s hospital in Ukraine; they committed war crimes in Syria; and the government has used, on at least two occasions, a weapons-grade nerve agent called Novichok, in assassination attempts. Putin keeps pushing the boundaries of acceptable behavior.

Here I am reminded of a quote from the great cosmologist and science communicator Carl Sagan. Writing in his 1993 book Pale Blue Dot, Sagan argued that

We are sometimes told that this or that invention would of course not be misused. No sane person would be so reckless. This is the “only a madman” argument. Whenever I hear it … I remind myself that madmen really exist. Sometimes they achieve the highest levels of political power in modern industrial nations. … In the winter and spring of 1945, Hitler ordered Germany to be destroyed—even “what the people need for elementary survival”—because the surviving Germans had “betrayed” him, and at any rate were “inferior” to those who had already died. If Hitler had had nuclear weapons, the threat of a counterstrike by Allied nuclear weapons, had there been any, is unlikely to have dissuaded him. It might have encouraged him.²

If a future in which Putin launches a nuclear strike becomes reality—this very well could be our reality, the timeline in which we exist—the consequences for humanity would be catastrophic. The most obvious reason concerns the immediate destruction and radioactive fallout, which could contaminate large areas with lethal doses of radioactive particles. Historically speaking, the first time many people came to realize that radioactive fallout from a nuclear conflict could affect individuals far from the detonation site was in 1954, after the U.S. detonated a massive thermonuclear weapon in the Marshall Islands that had an explosive yield 2.5 times larger than expected. Not only did 23 Japanese fishermen downwind suffer acute radiation poisoning (thus causing an international incident), but radioactivity was detected around the entire world. This demonstrated that even a relatively small-scale war with thermonuclear weapons (or “H-bombs”) could blanket the planet with DNA-mutating radiation. As the philosopher Bertrand Russell and his friend Albert Einstein wrote in their 1955 Russell-Einstein manifesto, the last document that Einstein put his signature to before passing away:

No doubt, in an H-bomb war, great cities would be obliterated. But this is one of the minor disasters that would have to be faced. If everybody in London, New York, and Moscow were exterminated, the world might, in the course of a few centuries, recover from the blow. But we now know, especially since the Bikini test [of the 1954 Marshall Islands incident], that nuclear bombs can gradually spread destruction over a very much wider area than had been supposed. … No one knows how widely such lethal radio-active particles might be diffused, but the best authorities are unanimous in saying that a war with H-bombs might possibly put an end to the human race. It is feared that if many H-bombs are used there will be universal death, sudden only for a minority, but for the majority a slow torture of disease and disintegration.

To which they added (in dated language) that “we have found that the men who know most are the most gloomy.” Indeed, the Bikini test triggered a pervasive feeling among intellectuals and the public alike that I would describe as “panic”: many leading scientists, including those who had helped design and build the first atomic bombs, became extremely concerned that humanity really might annihilate itself in the near future by converting Earth into a vast radioactive graveyard. But nuclear fears declined in 1963, one year after the Cuban Missile Crisis—described by Arthur Schlesinger as “the most dangerous moment in human history”—when the Soviet Union and U.S. signed the “Partial Nuclear Test Ban Treaty.” Tensions eased, and the Kremlin and Pentagon installed a direct connection between them, popularly called the “red telephone,” which still exists today, as a means for keeping communications open to resolve crises and avert catastrophe.

Then, in the early 1980s, something important happened: two scientists, Paul Crutzen (who also helped establish that CFCs destroy the ozone) and John Birks, discovered that radioactive fallout might not be the most dreadful consequence of a nuclear war. Instead, we should be even more concerned about the possibility that nuclear explosions ignite firestorms, or conflagrations with gale-force winds, one of which was actually started by the atomic bomb dropped on Hiroshima. These firestorms are so hot that they can, through convection, lift large quantities of black soot high up into the atmosphere—above the layer in which all the weather we experience here on the ground occurs. Since weather is one way that particles in the lower atmosphere are removed, black soot circulating high above this weather can remain aloft for very long periods of time.

This is bad because black soot would act like a blackout curtain, blocking incoming light from reaching Earth’s surface, thus causing temperatures to plummet and plants to stop photosynthesizing. Without plants, the food chain collapses, followed by civilization; humanity might not even survive this “nuclear winter” scenario. As Sagan explained in a 1983 article published in Foreign Affairs, the “cold, dark, radioactivity, … and ultraviolet light following a nuclear war … would imperil every survivor on the planet. There is a real danger of the extinction of humanity.” In a different article published the same year he declared:

There is little question that our global civilization would be destroyed. The human population would be reduced to prehistoric levels, or less. Life for any survivors would be extremely hard. And there seems to be a real possibility of the extinction of the human species.

It is unclear whether Putin is cognizant of this danger, whether he understands that even a limited nuclear exchange could pose a direct threat to the entire human species. Consider that, according to a study published in 2007, “a small-scale, regional nuclear war could kill as many people as died in all of World War II and seriously disrupt the global climate for a decade or more, harming nearly everyone on Earth.” As the authors of the study wrote, a nuclear war in the subtropics involving just 100 Hiroshima-sized bombs would

generate substantial global-scale climate anomalies, although not as large as the previous “nuclear winter” scenarios for a full-scale war. However, indirect effect on surface land temperatures, precipitation rates, and growing season lengths would be likely to degrade agricultural productivity to an extent that historically has led to famines in Africa, India and Japan after the 1784 Laki eruption or in the northeastern United States and Europe after the Tambora eruption of 1815 [which resulted in the “Year without a Summer” the following year]. Climatic anomalies could persist for a decade or more because of smoke stabilization, far longer than in previous nuclear winter calculations or after volcanic eruptions.

Of course, Putin using tactical nukes in Ukraine might not provoke a nuclear response from NATO, but who feels comforted by the possibility that it wouldn’t? As a recent article in the Bulletin of the Atomic Scientists states, “the notion that a nuclear war can be ‘limited’ is dangerous. In practice and in the fog of war, once nuclear weapons are used in a conflict involving nuclear-armed adversaries, there is no guarantee it would not quickly become an all-out nuclear conflagration.” What’s worse—zooming out from the current geopolitical predicament for a moment—is that, as the German philosopher Günther Anders pointed out in 1957, since nuclear weapons cannot be uninvented, this is a predicament that humanity can never escape. Any day, the actions of a “mad man” (as Sagan put it) or an error like what happened in 1995 could end the human adventure forever. To quote John F. Kennedy’s eloquent words, eerily spoken one year before the Cuban Missile Crisis:

Every inhabitant of this planet must contemplate the day when this planet may no longer be habitable. Every man, woman, and child lives under a nuclear sword of Damocles, hanging by the slenderest of threads, capable of being cut at any moment by accident or miscalculation or by madness.

But is it even possible to contemplate this day? To grasp the threat in a way that’s morally and emotionally commensurate with its seriousness? This is where the philosophy of Anders, in particular, can help. In an insightful paper on nuclear omnicide, Anders argued that the onset of the Atomic Age has turned every person on the planet into “inverted Utopians.” Whereas “ordinary Utopians are unable to actually produce what they are able to visualize,” he wrote, “we are unable to visualize what we are actually producing.” This is the “basic dilemma of our age” that “defines the moral situation of man today,” namely, that “‘we are smaller than ourselves,’ incapable of mentally realizing the realities which we ourselves have produced.” He elaborated:

The apocalyptic danger is all the more menacing because we are unable to picture the immensity of such a catastrophe. It is difficult enough to visualize someone as not being, a beloved friend as dead; but compared with the task our fantasy has to fulfill now, it is child’s play. For what we have to visualize today is not the not-being of something particular within a framework, the existence of which can be taken for granted, but the nonexistence of this framework itself, of the world as a whole, at least of the world as mankind. Such “total abstraction” (which, as a mental performance, would correspond to our performance of total destruction) surpasses the capacity of our natural power of imagination.

A psychological consequence of this is what Anders called “Apocalyptic Blindness,” whereby the divergence between our capacity to destroy and our ability to imagine has become so great that we are simply, by our very natures, unable to properly register the danger. We cannot adequately comprehend the true magnitude of nuclear self-annihilation, the stakes of human extinction, and this leads us to not take the risk seriously enough. Not only would the nuclear winter scenario kill everyone alive today, Anders noted, but it would eliminate the possibility of future generations and permanently erase the memories of all those who came before us—in his words, a “second death.” According to Sagan, writing in 1983, if humanity persists for another 10 million years and the population remains stable, there could come to exist another 500 trillion future people. This is a conservative estimate. Our extinction would also foreclose the further development of science, the arts, and morality, which some philosophers argue would constitute an extra tragedy above and beyond the loss of any number of individuals.

It could be that Russia’s invasion of Ukraine is the first sentence of the last chapter of our collective story on Earth—who knows? But it’s a possibility worth taking seriously. For Anders, the first step toward eliminating the nuclear threat is overcoming our Apocalyptic Blindness, our refusal to acknowledge that the danger is real and the consequences would be catastrophic. To do this, he argued that we must strive, every day, as best we can, to imagine the enormity of our disappearance in a nuclear holocaust. “Our imperative,” he wrote, must be to “‘Expand the capacity of your imagination,’ [which] means, in concreto: ‘Increase your capacity of fear.’ Therefore: don’t fear fear, have the courage to be frightened, and to frighten others, too. Frighten thy neighbor as thyself.”

Is fear really the best response? The answer is that it depends. Anders had a very particular notion of fear in mind—specifically, a kind of fear that motivates rather than incapacitates. In his words, what we need is “1) a fearless fear, … 2) a stirring fear, since it should drive us into the streets instead of under cover, 3) a loving fear, not fear of the danger ahead but for the generations to come.” Standing before the threat of nuclear conflict, individuals must choose activism rather than nihilism, we must make our voices heard: “A nuclear war cannot be won and must never be fought.” There is no law of nature according to which human self-annihilation is inevitable—every single threat facing us could be surmounted, if only the political will could be summoned. Climate change is solvable. Nuclear war is preventable. Even asteroids can be deflected away from our planet. The first step toward becoming an activist for the preservation of our species, though, is understanding the true gravity of the situation humanity currently finds itself in.

1. There is a complication, though: what is anomalous in one generation often becomes the norm to the next, and consequently children born today might never fully appreciate the immense richness of the biological world in times past. This has been called “shifting baseline syndrome,” and it is related to the notion of “creeping normality.” ↩

2. Indeed, the deputy director of the Atlantic Council’s Scowcroft Center for Strategy and Security recently said: “I find it hard to imagine Putin accepting a complete military defeat without him trying to use nuclear weapons first. … I think he sees limited nuclear use as more attractive than accepting defeat.” ↩