South Korean President Yoon Suk-yeol’s aid proposal was "as stupid as trying to dry the dark blue ocean and turn it into a mulberry field,” ...

Deep in the loamy soil of forests around the world, there exists a fungus called the honey mushroom that makes its living on death. A parasite that preys on weak trees, it sucks its victims dry of nutrients, then feasts on their postmortem flesh. Orchards and vineyards have fallen to it; gardeners, farmers, and foresters spend their days fruitlessly fighting the pesticide-resistant scourge. Although the bulk of the fungus’s mass is underground, its devastation is visible to anyone who’s flown over the gray, balding patches of woodland where the pathogen has felled its hosts.

The honey mushroom is also an exemplar of the extreme forms that life can take. Thousands of years ago, one honey-fungus species, Armillaria ostoyae (also known as Armillaria solidipes), birthed a spore that settled in what we now think of as Oregon, started to spread, and never stopped. “It was just extremely, extremely successful at growing,” says Adriana Romero Olivares, a mycologist at New Mexico State University. “And so it got extremely, extremely large.” Today, that individual fungus inhabits roughly 2,400 acres of earth. Nicknamed Humongous Fungus, it is one of the planet’s largest known organisms, and the biggest ever recorded by area on land.

The honey fungus is an unlikely candidate for such a title: It’s a microbe with an unsettling MO. But Humongous Fungus is also scrappy, flexible, indefatigable—a survivor—and its reach may yet keep creeping out. “As long as you have trees, then this fungus will thrive,” says Mee-Sook Kim, a research plant pathologist at the U.S. Forest Service. “It has, theoretically, indefinite growth potential.” Humongous Fungus has two main rivals for the title of World’s Largest Organism; it may outlast both, not just because it’s resilient, but also because it is unusually well equipped to profit from this planet’s ongoing epidemic of death.

The criteria that delineate Earth’s biggest organisms aren’t terribly scientific. “We don’t spend a lot of time precisely measuring ‘largest’ to win a competition, per se,” says Paul Rogers, an ecologist at Utah State University. Still, it’s generally accepted that three contenders are vying for top billing: Humongous Fungus, in Oregon’s Malheur National Forest; Pando, the gargantuan grove of quivering aspen in central Utah; and a recently discovered seagrass in Shark Bay, off the western coast of Australia.

All three are objectively ginormous, covering many acres of land and weighing thousands of tons; they are genetically identical throughout, each supposedly sprouted from a single unit of life. The Australian seagrass, which blankets roughly 49,000 acres of ocean floor, spans more area than Humongous Fungus. And although the shroom has colonized more territory than the Very Big Boy that is Pando, a 106-acre male aspen clone, the tree grove clocks in at about 6,500 tons, probably besting the water-hoarding shroom in sheer “dry weight,” Rogers told me. (To be fair, the fungus and the seagrass are so tough to access that it’s difficult to estimate their mass.) But Humongous Fungus still has plenty to boast about, according to the totally unbiased mycologists I spoke with.

If Armillaria has a home-field advantage anywhere, it’s underground. The fungus’s rhizomorphs—black, ropy, root-like growths—can snake through the soil for many meters, sniffing for vulnerable trees. Once the fungus finds a suitable host—just about any tree or woody plant—it infiltrates the root system, then fans out into felty white filaments beneath the bark that gush out enzymes, transforming tissues into mush, says Jim Anderson, a mycologist at the University of Toronto. The fungus is so tenacious that it has little trouble just “burrowing straight through” trees’ outermost shields, including bark, says Debora Lyn Porter, an engineer at the University of Utah, who’s investigating the rhizomorphs: “It’s super, super strong.”

[Read: The secrets of the ‘Humongous Fungus’]

Honey mushrooms aren’t the only fungi with rhizomorphs. But Armillaria’s versions “are particularly tough,” says Laura Bogar, a mycologist at UC Davis. They can soak up minerals from the soil and weaponize them; they can withstand most fungicides—they “basically eat that stuff for breakfast,” Anderson told me. Porter has even tried boiling rhizomorphs or dunking them in acid, to little effect. And starved of living trees, the structures can go dormant in the soil for decades, waiting to latch on to their next arboreal snack. When asked what can be done to rid plants of the fungus, Anderson told me that his best answer is “not much.”

All of that helps explain the behemoth sizes the fungus can reach. Oregon’s Armillaria expanse is the biggest individual recorded, but plenty of other ginormous specimens have been documented, including one on Michigan’s Upper Peninsula, which Anderson has studied for years. More, yet undiscovered, may lurk beneath the ground.

Pando and the seagrass, meanwhile, seem a bit weirder than the rest of their kind. Other clonal aspen groves exist—a quirk of the trees’ unusual horizontal roots, which sprout their own stems—but very few even come close to rivaling Pando in mass. Part of Pando’s success seems genetic: It carries an extra copy of its genome, a trait that’s been linked to fast growth. Chance also played some role. Thousands of years ago, an aspen seed likely happened upon a super-stable patch of soil and just never collided with any conditions that halted it. And there’s quite a strong strong case for the seagrass being unique, says Elizabeth Sinclair, a biologist at the University of Western Australia who helped unveil the plant’s genetic makeup. It’s a hybrid between two species and contains double the genetic information of its parents; likely sterile, it has expanded by repeatedly xeroxing itself.

A freak event could easily take aspen or seagrasses out of the big-bodied race. Armillaria, however, just needs to keep on Armillaria-ing to stay in contention. The fungi will likely be able to withstand some of the twists and turns of a fast-changing planet: droughts, wildfires, storms, rising temperatures, and the many human interventions that are making forests less habitable. Armillaria “will probably outlive a lot of things, including us, including a lot of the plants it prefers,” Romero Olivares told me.

Armillaria is not a villain. A decomposer that prunes maladapted trees and returns their nutrients to the soil, it can play “quite a beneficial role,” Kim, of the Forest Service, told me. This antihero is constantly reinventing its ecosystem and buoying forest health.

But you can also see the fungus as a mirror for our callousness. When offered up trees that are fragile, honey mushrooms will take the easy meal. As rising temperatures and droughts strain forests, as invasive insects gnaw through wood, as humans cull stands through logging and slash the diversity of plants, as fire suppression leaves flammable trees in too-tight clusters, “that’s all more food and fodder for the growth of Armillaria,” says Ariel Cowan, a fire ecologist, mycologist, and forest-ecosystem scientist at Oregon State University.

That Humongous Fungus has reached even its current size, Cowan told me, is “a symptom of a larger problem”—that is, people. Had humans, for instance, allowed more natural fires to burn and thin forests, the fungus would still probably be there. It would just be more svelte, less problematic—a passive recycler rather than a bringer of death. “It’s taking advantage of the fact that we’re messing up ecosystems,” Romero Olivares told me. The worse we treat trees, the bigger the fungus gets.

The problems that Armillaria capitalizes on are putting other big organisms in jeopardy. In Utah—where humans have driven out predators such as wolves—wild mule deer and domestic cattle are crunching too quickly through Pando’s young aspen; the grove can no longer replace its clonal trees as fast as they are being lost. The traits that helped the aspen win out for thousands of years are now “working to its detriment,” Rogers said, and the grove is dying. That’s the double jeopardy of being so big: Flip to an environment the life-form doesn’t like, and the whole enterprise goes down.

The prognosis for the Australian seagrass is better, but not necessarily good. Thanks to its double-size genome, it has “a wide range of conditions that it can cope with,” Sinclair told me. The marine plant even survived a massive heat wave that swept through Shark Bay about a decade ago and “cooked” a whole swath of underwater life, she said. “But I don’t know how much longer it can do that if climate change keeps progressing.”

[Read: The world needs to start planning for the fire age]

Eventually, the world may grow too harsh for even the honey mushroom; no one yet knows where its limits lie. Cushioned underground, the fungus is buffered from the elements. But it does depend on its hosts. At some point, Bogar told me, “what happens to plants will also happen to the fungi.” Contemplating such a future is sobering, Anderson said: “A world in which conditions managed to do away with Armillaria would be a truly hurting place for us.”

As Rogers monitors Pando’s withering state, he has grappled with what it would mean to lose something of such staggering size. Pando, Humongous Fungus, and the seagrass all thrived unencumbered for millennia. Any recent reversals of fate, he said, can really only “point the finger directly back at us.”

The death of a plant or fungus, however large, may feel less wrenching than that of, say, a blue whale: an animal with a brain and a heartbeat, contained by skin and founded in bone. We can observe such a demise in one dose. But the perishing of a giant organism is never siloed. Pando, Humongous Fungus, and the seagrass are so colossal that they have interlaced themselves with their surroundings; their loss would imperil the flora and fauna that depend on them. If and when they die, it will mean the massacre of an ecosystem—the vanishing of not one, but many.

Russian president tells Kim closer ties will strengthen regional security, reports North Korean state media.

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Reading is hard right now. The pandemic has pushed our already scattered attention spans to a crisis point. But even before 2020, stressors such as political chaos and the allure of our phones made it harder and harder to find the time and focus to get lost in a book. Even when we’re not living through a distracting moment, we will inevitably have personal fallow periods when reading as a habit and a respite just doesn’t happen.

Certain writing is able to grab us and shake us out of these ruts—by presenting a breakneck adventure we feel compelled to see through; by gently opening us back up to the thrill of a good story; by allowing us to spend time in the mind of a fictional character. When they appear to us at the right moment and in the right way, these books can act as a bridge that leads us back to the rewards of literature. Below, our staff members have compiled 12 books that rekindled our love for reading after a dry spell.

Vintage

Heartburn, by Nora Ephron

After I had my twins in the summer of 2020, when my brain was as sludgy as risotto and I couldn’t imagine finishing a CNN chyron, let alone a novel, my very brilliant friend Annalisa recommended Heartburn as a “gateway” back into reading. I finished it in a few days, sucking up the chapters like air or a cocktail. The book is a lightly (very lightly) fictionalized version of Ephron’s own devastating marital crisis, when she discovered that her husband, the former Washington Post reporter Carl Bernstein, was having an affair with a mutual friend while Ephron was pregnant with their second child. Somehow, it’s hysterical. Ephron’s tone throughout is part stand-up comic, part beloved friend sending a bitchy, meandering email. In one paragraph, her thoughts turn from despair to suicidal ideation to the habits of “neurasthenic,” poetic sad girls to this take on that famous genre: “Show me a woman who cries when the trees lose their leaves in autumn and I’ll show you a real asshole.” Did I mention that recipes are folded into the text? An actually perfect novel. — Sophie Gilbert

Celadon

The Plot, by Jean Hanff Korelitz

Recently, during a particularly grim stretch of months, I was desperate to get lost in a book. I kept searching for something that would echo what I was feeling: serious reflections on sickness, grief and loss, the world ending. But I couldn’t finish anything. Getting to the last page always seemed like hiking up a mountain; it would be worthwhile, even beautiful, but also exhausting. When I read The Plot, I realized I’d been picking the wrong material. The title of Korelitz’s twisty thriller feels like a wink to the reader. It is, in fact, a plot-driven book about the power of a good plot. (Things kick off when a writer steals a dynamite story line from a dead person.) That’s not to say the book is only action; it plays with meaty questions about artistic ownership, gender, and creative identity. But Korelitz leans into the drama and the fun. Sometimes, when you want a book to take you away, you have to choose one that doesn’t hit home. — Faith Hill

Penguin

Intimations, by Zadie Smith

Reading about the pandemic may sound like a terrible idea for someone trying to move past the misery of the pandemic. But Smith’s Intimations, a collection of essays written during and about the isolation and anxiety of 2020, serves less as a bleak reminder of our social-distancing era and more as comforting evidence that even one of the most clear-eyed authors struggled to shape her thoughts. Some passages come off like first drafts, but that moved me: Smith seemed as reluctant as I was to contend directly with the virus’s toll, as torn as I felt about attempting to turn my dread into sourdough. Absorbing her musings, especially about writing, reassured me; her prose was as beautifully structured as ever, but she wasn’t forcing herself to find answers. At barely more than 100 pages long, Intimations is a literary compass, compact and unassuming, but essential to finding a way forward. — Shirley Li

[Read: The literature of the pandemic is already here]

New York Review Books

Turtle Diary, by Russell Hoban

Turtle Diary doesn’t move very fast. It doesn’t have any real dramatic tension, either: The book’s two melancholy and otherwise unconnected narrators, William and Neaera, encounter no obstacles in their shared quest to release three sea turtles living at the London Zoo back into the ocean. The zookeeper is an eager accomplice. Their journey across England, their charges tucked in the back of a rented van, is eventless. The turtles slip easily into the water and swim away. This is not a book that screams Don’t put me down! And yet, after I had spent more than a year with my attention frayed by the dual demands of editing stories about the pandemic and caring for my baby—after I had spent many months too distracted to think about books—I kept reading because of Turtle Diary’s calm, its quiet interiority. However undramatic, the turtles’ release is a transformative moment for both William and Neaera, and afterward, they feel more at ease in the world and with themselves. Only a book could capture the intimacy of a shift like that, and offer the pleasure of sharing in it. — Sarah Laskow

Graywolf Press

In the Dream House, by Carmen Maria Machado

To borrow the architectural metaphor that animates In the Dream House, this isn’t a memoir you read so much as one that you wander through, room by room. I toured it, so to speak, in less than a day, trying to wean my brain off social media and reacquaint it with the slow, analog pleasures of following a single narrative for an extended period. To tell a difficult story about domestic abuse within a lesbian relationship, Machado resorts to an unconventional, fragmented structure. A mesmerizing narrator, she weaves personal narrative with intelligent and often darkly funny interrogations of literary and pop-cultural tropes. Chapters are short and given intriguing titles such as “Dream House as Schrödinger’s Cat” and “Dream House as Noir.” (The chapter “Dream House as Famous Last Words” is simply the sentence “‘We can fuck,’ she says, ‘but we can’t fall in love.’”) The effect is accumulative and devastating, and the memoir’s many pieces add up to an inventive reckoning with cultural silence. — Lenika Cruz

[Read: The shadow pandemic]

Henry Holt and Co.

Goodbye, Vitamin, by Rachel Khong

After Ruth’s fiancé breaks up with her, she quits her job, returns home, and helps care for her father, who is in the early stages of Alzheimer’s. It sounds like a bummer of a premise, but Goodbye, Vitamin is actually one of the most life-affirming books I’ve ever read. When I’m in a reading rut, it’s usually because of stress, which leaves me unable to focus on a dense narrative. This novel is the perfect antidote: It’s a short read, and most scenes are less than a page long; many are just a couple of lines. It’s a story told in small everyday moments, and the knowledge that Ruth has limited time left with her father imbues each with meaning. Its comforts are deeper than escapism; by showing, never telling, it demonstrates that all the moments of our stupid little lives, even the hard and mundane ones, add up to something profound. But it’s really funny too! Khong expertly balances the silly and the sublime until the last page—even now, years after I first read it, thinking of the book’s final lines can make me cry. — Julie Beck

William Morrow

All About Love: New Visions, by bell hooks

In the blustering December days following the death of the Black feminist titan bell hooks, the first wave of the Omicron variant rapidly overtook New York City. Under such foreboding conditions, I rarely seek out nonfiction that isn’t explicitly work-related. But in reading so many moving tributes to hooks, I was compelled to revisit All About Love: New Visions, a brisk, personal read. Interspersing cultural analysis with anecdotes from her own life, hooks ponders what love could look like in action. “When we choose to love we choose to move against fear—against alienation and separation,” she writes. It’s at once an incisive critique of elevating romantic connections above all other kinds and a guide to employing what hooks calls a “love ethic” as a communal balm. This is the kind of nonfiction that feels like an invitation. All About Love holds the same enthralling power over me now as it did when I first encountered it as a college freshman. When I arrived at its final pages again, I was comforted by the thought that more awaited me—in the rest of hooks’s Love Song to the Nation trilogy, in her broader oeuvre, and in the other nonfiction it guided me back to. — Hannah Giorgis

Vintage

Trio, by William Boyd

During the Trump era, I stopped reading books. Maybe this is understandable. The human brain is no more designed for a sustained assault on its attention than it is for metabolizing Froot Loops, and that’s essentially what Donald Trump’s presidency required: the unremitting ingestion of Twitter’s neon birdseed. Yet still I was alarmed. For two-plus years, I’d been a daily book critic at The New York Times. How on earth did I lose the skill to stay with a novel? Two things got me reading again: the election of a dull, steady, Twitter-indifferent president, which gave me the permission I needed to lose myself in fiction, and the arrival of a galley of Trio. It takes place in Brighton during the swinging ’60s, and though its scope is less ambitious than some of Boyd’s cradle-to-grave pseudo-biographies, it’s great fun nonetheless, focusing on a trio of characters (an actor, a writer, and a film producer) involved in the desperate and occasionally redeeming project of making art. I was instantly transported by their excesses, frailties, and deceptions. Boyd, an expert conjurer of worlds, writes with his customary energy and wit. Plus, one of his minor devils has the unimprovable name of Janet Headstone. Who could resist? — Jennifer Senior

[Read: The exquisite pain of reading in quarantine]

Bloomsbury

Piranesi, by Susanna Clarke

I read Clarke’s jewel of a novel during our first pandemic winter. At a time when creative virtuosity was the last thing on most of our minds, Piranesi floored me with its imaginative heft. A man called Piranesi lives in a house with many rooms that is sometimes flooded by the sea. He can’t remember how he got there, but he occupies his time by mapping its cavernous, statuary-filled halls. He fishes for food and makes coverings for his feet. (He wonders, at one point, whether he can knit socks from seaweed. He decides he cannot.) He also catalogs and gives names to the few people he knows or eventually discovers exist: the Other, the Prophet, 16. The reveal—why Piranesi is in the house, who his compatriots are, why his memory is so hazy—is wildly inventive. Clarke explores grand themes (consciousness, hubris) with tenderness and contrasts brilliantly austere environs with her protagonist’s warm curiosity, which registers like a beating heart. Reading along, I felt the pleasure of trusting a master storyteller; gently, slowly, she illuminated the dark until I was, like Piranesi himself, standing in the bright light of the world outside the house. — Jane Yong Kim

Tor

The Three-Body Problem, by Liu Cixin

After numbing my early-pandemic terror by getting lost in video games, I became immersed in a story that was, in part, about gaming through the apocalypse. Liu’s sci-fi landmark, The Three-Body Problem, opens with scenes from China’s Cultural Revolution in the ’60s and then traverses decades in which aliens seem to be messing with Earthly affairs, leading humankind’s brightest minds to treat their everyday reality as a puzzle to be solved. One character becomes mesmerized by a multiplayer virtual world that seems to hold clues about the mounting glitchiness of meatspace. Other characters devote themselves to quests—for hidden knowledge, for interstellar connection, for the reform of our species—with the kind of fervency that blots out all other pursuits. Devouring the book felt like completing a series of mind-bending challenges on the way to some unimaginable final level. But Liu’s exact prose and restless, point-of-view-switching narrative style paid off the obsession in a way that no game could. — Spencer Kornhaber

[Read: What happens if China makes first contact?]

Greenwillow Books

The Thief, by Megan Whalen Turner

I felt like a ragged cuticle in 2020—exposed, inflamed, sensitive. Everything was overstimulating, even books. As the year dragged on, I decided that if reading was impossible, I’d try rereading. I began with Turner’s 1996 novel, which I’d loved in middle school but mostly forgotten. Set in a preindustrial Hellenistic world with a vividly imagined history and mythology, the book’s titular pickpocket, Gen, is a charming scoundrel who’s sprung from jail and drafted for a mysterious mission. The reasons why he travels across the country, and what his companions need a thief for, trickle out slowly alongside intrigue and banter. Turner’s story is heavy on politics and reality, which makes its mysterious supernatural implications irresistible. And when I reached the crucial, climactic twist that gives the entire journey a new meaning, the revelation of a character’s true identity and my giddy original discovery of it more than a decade ago rushed back. I immediately picked up its sequel, just as I had the first time around, and read all the way through the five other books in the series—ending with the serendipitously released 2020 conclusion, Return of the Thief. — Emma Sarappo

Anchor

The Diary of a Young Girl, by Anne Frank

Early in the pandemic, I noticed that my daughters, who were 10 and 7 then, had stopped reading. Once the snow-day giddiness of those early weeks faded and some semblance of routine returned, they seemed incapable of losing themselves in books. I couldn’t blame them; my reading time was mostly spent refreshing websites that gave the numbers of the infected and dead. And then, one evening, I picked up Anne Frank’s diary. The choice was maybe morbid (and it’s possible they weren’t quite ready for it), but I sat on the floor in their room and began reading a few entries to them before bed. I’d forgotten how the diary starts with Anne in freedom, all earnestness and schoolgirl obsession. The girls loved it. And then Anne’s life begins to contract. What menaced her was so much more dangerous and deadly than COVID; they understood that. But they also couldn’t help relating: Anne peeks out the window of her attic to catch a glimpse of sky and rooftop. At one point, she wonders, “When will we be allowed to breathe fresh air again?” They kept asking for one more entry, and I kept wanting to slow down. Reading was giving them pleasure again, but I knew, as they didn’t yet, how her story ended. — Gal Beckerman

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On the brink. That’s how we tend to think of humanity’s predicament during the most dangerous moments of the nuclear era. But as Thomas Schelling, the godfather of nuclear strategy, once pointed out, the phrase is misleading. The nuclear frontier is not “the sharp edge of a cliff where one can stand firmly, look down, and decide whether or not to plunge,” he wrote, but rather “a curved slope that one can stand on with some risk of slipping”—the slope getting steeper and riskier “as one moves toward the chasm.” Now the slope is getting steeper before our eyes.

That’s not just because of the potential for Russian President Vladimir Putin to use nuclear weapons in a desperate effort to avert defeat in Ukraine. It’s also the result of a threat that isn’t making many headlines but that experts are currently concerned about: North Korea’s development of tactical nuclear weapons—less explosive, shorter-range arms designed for use on a battlefield.

North Korea has been pursuing tactical nuclear weapons for many years, but the latest chapter in this story begins in January 2021, when the country’s leader, Kim Jong Un, explicitly pledged to build such weapons. Then came Pyongyang’s April 2022 test of a short-range missile expressly intended to be wielded as a tactical nuke, followed by cryptic June military announcements that some analysts interpreted as an indication that Kim is planning to deploy the weapons to his frontline artillery units. North Korea watchers expect the country to conduct its seventh nuclear test any day now, which would most likely be aimed at further honing small warheads that could be mated with shorter-range missiles.

If those predictions bear out, North Korea’s next nuclear test would herald what some scholars have dubbed a “third nuclear age.” The first age was dominated by the Cold War between the United States and Soviet Union, the second by post–Cold War dynamics among various emerging and aspiring nuclear-weapons powers.

[From the July/August 2022 issue: We have no nuclear strategy]

In a prescient 2019 essay, the scholars Nicholas L. Miller and Vipin Narang identified three main components of this new, third nuclear age: “renewed nuclear competition among several great powers” as arms-control agreements fall apart and these countries modernize their arsenals, the “emergence of new nuclear powers” (potentially including both U.S. allies and adversaries), and “a greater tolerance for escalation among existing nuclear powers.” North Korea’s work on tactical nuclear weapons testifies to the second and third dimensions.

This dangerous moment combines the challenges of great powers competing with and seeking to deter one another in the nuclear realm (the hallmark of the first nuclear age) with the challenges of stopping the proliferation of nuclear weapons (the focus of the second)—plus destabilizing new weapons systems and vanishing international cooperation to keep any of it in check.

The third nuclear age ushers the world into “truly uncharted waters,” the scholar David Cooper has observed. “Everything we think we know about nuclear weapons—deterrence, coercion, etc. … is based on a very short, finite history from two of the world’s most stable periods: the frozen, bipolar stalemate of the Cold War and then the subsequent … ‘unipolar moment’ of the post–Cold War world where the United States essentially was unrivaled in power.”

Tactical nuclear weapons are often described as “small” nuclear weapons, but that’s something of a contradiction in terms—like saying not to worry about the small asteroid barreling toward your town. The smallness holds only when compared with the kinds of “strategic” nuclear weapons that the U.S. and the Soviet Union threatened to obliterate each other with during the Cold War. Many tactical nuclear weapons in the American and Russian arsenals pack more potential explosive power than the U.S. atomic bomb that killed roughly 70,000 people in Hiroshima, although these explosive yields can be adjusted to lower levels.

After the Cold War, the U.S. scaled back its tactical nuclear weapons amid the triumphalism and diminished security threats of that period. But Russia largely maintained its stockpile, which is currently about nine times the size of America’s.

And as Ankit Panda of the Carnegie Endowment for International Peace has argued, if North Korea adopts tactical nuclear weapons, it would “manipulate [Schelling’s] slope” and “invite the United States and South Korea to stand on it.” North Korea is already predisposed to use its nuclear weapons early in a conflict with more powerful adversaries. The addition of tactical nukes, given their less destructive nature relative to strategic nukes, would further lower the bar for North Korean use of nuclear weapons. Deploying tactical nukes could involve Kim delegating some authority for command and control of those weapons to lower-ranking military commanders, particularly in wartime, and storing the weapons at more military bases throughout the country—which could significantly increase the risks of nuclear use as a result of accidents or miscalculations.

In, say, a non-nuclear conflict sparked by an act of North Korean aggression, Kim or one of his commanders, operating in the information-distortion field that is North Korea, could mistake a U.S. or South Korean retaliatory attack (or even something mundane, such as a civilian plane nearing North Korean airspace) for a more existential military offensive to wipe out the regime or its nuclear-weapons arsenal. They could respond by firing tactical nuclear weapons at U.S. or South Korean targets, leaving Washington and Seoul unsure about how to respond—particularly given U.S. qualms about again crossing the nuclear threshold and North Korea’s suspected capability to target the U.S. mainland with longer-range nuclear weapons.

North Korea could also deliberately turn to tactical nuclear weapons during an intensifying or stalemated conflict in an effort to spook its enemies and compel them to back down—an “escalate to de-escalate” strategy that the Russian military is thought to embrace.

[Eric Schlosser: What if Russia uses nuclear weapons in Ukraine?]

The suddenly more real (if still very low-probability) prospect of Russian nuclear use in Ukraine is forcing policy makers, unpracticed in nuclear strategy and planning, to think hard about response options to such a brazen but bounded crossing of the nuclear threshold. In a similar vein, U.S. and allied officials need to proactively craft new policies and strategies for how to deter North Korea from using tactical nuclear weapons—and how to respond should deterrence fail. That could involve, for example, the U.S. and South Korean militaries making their bases less attractive targets for Pyongyang. It could also entail Washington and Seoul shifting their focus from the long-standing but now-quixotic goal of “denuclearizing” North Korea to engaging it in talks aimed at reaching arms-control agreements, reducing the threat that each side perceives from the other, managing crises before they spiral out of control, and mitigating the chances of a nuclear conflict erupting.

Former U.S. President Ronald Reagan and the former Soviet leader Mikhail Gorbachev famously declared that “a nuclear war cannot be won and must never be fought.” That reassuring sentiment was affirmed as recently as earlier this year by the five internationally recognized nuclear-weapons states. But in this third nuclear age, the line needs a corollary that recognizes the harsh realities of the times: Some nuclear-weapons states may indeed believe that a nuclear war can be won—and thus that one could be fought.

We often talk about the potential use of nuclear weapons in apocalyptic terms—as an act that would destroy the whole world. But that description of nuclear war as unthinkably horrific is a legacy of the Cold War. Limited use of nuclear weapons—use that could inflict tremendous destruction and shatter international norms but not destroy the world—is unfortunately thinkable. At the very least, it is incumbent upon policy makers to act as if it is thinkable; the very concept of tactical nuclear weapons is, in fact, premised on the idea that limited nuclear war is thinkable. We need to plan for such scenarios—even as we expend every effort to prevent them from materializing.