Our Warming Planet Is a Petri Dish for New and Deadly Microbes

On a sweltering morning last July, Vernon Spear, a burly eighty-five-year-old with thinning gray hair, went to check a chicken-wire crab trap that was hanging from a dock in Cambridge, Maryland. Spear is a lifelong resident of the Eastern Shore, near where the Choptank River flows into the Chesapeake Bay. He lives less than fifty yards from the dock. He was pleased to find that the trap held six feisty blue crabs, a local delicacy that he likes to steam and sprinkle with Old Bay. As Spear reached in, however, he scraped his arm on some metal, drawing blood. He wasn’t worried; he’d been scratched many times before. But, in the hours that followed, Spear’s arm began to turn violent shades of purple and red. His wife, Lea, thought it looked like he’d been badly burned. Soon his arm swelled up—liquid appeared to be pooling under the skin—and he rushed to his local emergency room. A clinician suspected an infection of Vibrio vulnificus, which under a microscope looks like a kidney bean with a tail. It is popularly known as flesh-eating bacteria.

When V. vulnificus enters a wound, it damages blood vessels, causing them to leak plasma into surrounding tissues. The immune system tries to protect the body by calling in clotting cells to halt the leaking; in the process, the cells cut off blood flow, prompting flesh to become necrotic. The bacteria can cause shock, sepsis, and multi-organ failure. Infections that reach the bloodstream prove deadly at least fifty per cent of the time.

A medical helicopter arrived within twenty minutes. Spear was flown to the R Adams Cowley Shock Trauma Center at the University of Maryland Medical Center, in Baltimore. There was no question that he would need surgery. Rather, his doctors wondered if they would be able to save his life. Antibiotics on their own are of limited use against a V. vulnificus infection. The best way to control the bacteria is to cut away the affected flesh. Surgeons worked quickly to excise layers from Spear’s forearm. When he regained consciousness, hours later, he was aghast. He could see into his arm; the muscle and bone were exposed. “It was just a big hole,” he told me.

For most of Spear’s lifetime, infections of V. vulnificus north of Georgia were rare. Lately, however, the bacteria have killed people as far north as New York and Rhode Island. “What has happened is that the environment has changed,” Rita Colwell, a ninety-one-year-old microbiologist at the University of Maryland, told me. It’s not that the bacteria are migrating, she said. Low levels are always present where freshwater and salt water mix. But when water warms above fifty-nine degrees Fahrenheit V. vulnificus becomes more abundant, and above seventy-seven degrees its population soars.

When Colwell started sampling microorganisms in the Chesapeake Bay, in the late sixties, she occasionally heard about V. vulnificus infections in the area. A deadly case in the eighties made the Washington Post and the Baltimore Sun. “It was an astounding rarity,” she told me. Nowadays, about a dozen cases are confirmed in Maryland each year; the number increased by more than fifty per cent in the span of fourteen years. A 2023 study found that the season in which the bacteria are detectable now starts in early spring and extends into the fall. “This is insidious, and it’s happening to us,” Colwell said.

Climate change affects every life-form on Earth, but we tend to focus on how it impacts certain vulnerable species: polar bears, sea turtles, corals. Microorganisms are often omitted from the story of warming, even though they far outnumber plants and animals. In 2019, an international group of thirty-three scientists warned in the journal Nature that the “unseen majority” of life was being transformed by rising temperatures, and that humans would have to contend with the consequences. Microorganisms that infect us could become more common, and appear in new places. Billions of other microbe species could be affected, too. How would they respond when their environments shifted? “We’re dealing with the first life on Earth,” Antje Boetius, a co-author of the Nature paper, who serves as the president and C.E.O. of the Monterey Bay Aquarium Research Institute, told me. “Our planet is the test tube. We make it a bit warmer, everything will change.”

When scientists depict all of Earth’s species on a tree of life, the lineage of humans looks like a twig. Microbes—biological entities that are too small to see without a microscope, including bacteria, fungi, viruses, protozoa, algae, and archaea—take up most of the tree. Microorganisms are not passive occupants of our planet—they are co-creators of our environment. Microscopic algae produce much of the oxygen that we breathe. Various microbes process almost all the dead plants on the planet. “Without that very basic function, we’d all be sitting in a pile of leaves,” Steven D. Allison, an ecologist at the University of California, Irvine, told me. Microorganisms partner with plant roots, and with leaves that regulate the amount of carbon in the atmosphere; they are “the architects and the wardens of life on this planet,” A. Murat Eren, a microbial ecologist and computer scientist at the Helmholtz Institute for Functional Marine Biodiversity, in Germany, told me. (A soil bacterium is even responsible for making a compound called geosmin, Greek for “earth” and “odor,” which generates the distinctive scent that follows rain.)

What virtually all microbes have in common is that they are ubiquitous. Microbial ecologists have a saying, Boetius told me: Everything is everywhere. A single drop of seawater, for example, can contain a million microbes, including a hundred or more species of bacteria. Microbes colonize every plant and animal, living and dead; they live on frozen mountaintops, in searing volcanoes, and at the bottoms of the deepest caves and oceans. When scientists sampled clean rooms where NASA builds spacecraft, they managed to find two hundred and fifteen bacterial strains on the floors alone. Microbes even have their own microbes.

Meanwhile, microbes are constantly evolving. Many bacteria divide numerous times a day—and, crucially, accumulate mutations in the process. “Every division is an experiment in survival, with a slightly different genetic roll of the dice,” Eren said. Different types of microbes reproduce in different ways: bacteria and archaea duplicate themselves; viruses hijack the cells of other species; and some fungi reproduce sexually, whereas others transfer their DNA by releasing spores. But all of them can gain new traits over time, just as plants and animals do—only the microbes are much faster at it. (The gap between the rate of human evolution and the rate of microbial evolution, Eren said, is like “the difference between a drifting tectonic plate and an F-16 fighter jet.”)

In the late nineteenth century, William Dallinger, an English minister who experimented with microscopes, cultivated microbes called flagellates in warm water. He gradually increased the temperature to a hundred and fifty degrees, a level that once would have killed them. They adapted to such an extent that when they were put back in cooler water they died. Nearly a century later, scientists at Michigan State University bred Escherichia coli in a stark environment that contained barely any food. More than thirty thousand bacterial generations later, an E. coli lineage developed the ability to consume molecules known as citrates, which were previously inedible. The change was as extreme, a biological mathematician wrote, as if humans had developed the capacity to eat wood.

Our bodies, in turn, are constantly adapting to the trillions of microbes that surround us. Each of us has a microbiome—a universe of microorganisms living on us and in us—that helps digest food, stop infections, and make chemicals that the body needs. When microbes are beneficial or benign, we say that they’ve colonized us. When they are harmful, we say that they’ve infected us. Even then, our bodies adjust to their presence. Our immune systems develop new defenses, trying to kill germs that might otherwise kill us. But, in an era when the microbial world is changing rapidly, plants and animals may struggle to keep up. “We always ask: How are we going to adapt to a changing world?” Eren said. “The real question is: How are we going to coexist with microbes that have adapted to the new world?”

“So, the queen died, and after a brief period of anarchy a fledgling democracy started to emerge, but then there was a coup and the eventual rise of a brutal strongman, and long story short the honey tastes lousy.”

Cartoon by Emily Flake

Spear ultimately spent eight days in the hospital. Doctors watched carefully for any further darkening of the skin, which would indicate that the V. vulnificus infection was still spreading. The six blue crabs had been left in a pot on the stove. “Never got to eat them,” Spear told me.

In October, I watched Spear undergo a follow-up surgery in Maryland. He was under anesthesia, covered with drapes. Only his right arm and left leg were visible. I could see the aftermath of the infection: the entire length of his forearm was shiny and pink, like prosciutto. William Chiu, an acute-care surgeon, explained that he would be covering the wound with a thin layer of Spear’s own skin. (They sourced the skin from his left leg because he has a tattoo on his right.) I watched as another doctor slid what looked like a potato peeler along Spear’s thigh. He then rolled the resulting strip of skin through a mesher, an instrument that cuts geometric holes into tissue so it can expand to cover a larger area. Finally, he handed the skin graft to Chiu, who delicately stretched it over Spear’s arm.

After the surgery, I sat with Spear and his wife in the shock-trauma unit. He had an I.V. in his arm. He still seemed stunned that dipping his hand in the local river had nearly killed him. “We’ve never heard anything about not going into the water,” he told me. Despite the circumstances, he was in good spirits. He and his wife shared stories they’d heard about other V. vulnificus infections. A friend had said that his brother, a waterman, lost his leg to an infection. Their electrician had told them about a man on nearby Hoopers Island who contracted a fatal infection after being nicked by a crab shell. Spear’s wife worried about families who vacationed on the Eastern Shore. How would they know to avoid the water when they had open cuts or scrapes?

In the middle of our conversation, Spear suddenly exclaimed, “I don’t believe in global warming.” There was an awkward silence. I asked if he thought the weather had changed during his lifetime. He mulled this over and said, “It’s warm now, and it’s, what, October?” He leaned back onto his pillow and exchanged a glance with his wife. “We don’t have as harsh winters anymore,” he added.

In the opening scene of “The Last of Us,” a post-apocalyptic HBO series that débuted in 2023, an epidemiologist goes on TV to share his greatest fear: that fungi will adapt to warmer and warmer temperatures. Right now, most fungi grow best between fifty-four and eighty-six degrees; the human body hovers around ninety-eight. “Currently, there are no reasons for fungi to evolve to be able to withstand higher temperatures,” the epidemiologist says. “But what if that were to change?” A few scenes later, an elderly woman who is infected with a fungus develops a taste for human flesh.

After the episode aired, Arturo Casadevall, a microbiologist at Johns Hopkins University and the author of “What If Fungi Win?,” was flooded with e-mails. Casadevall is perhaps best known for a theory that warm-blooded creatures are protected from fungi by a “thermal barrier.” Most of the microbes that infect humans are either bacteria or viruses; we’re largely spared from fungal diseases. (Our immune systems also play a key role in protecting us.) To plants and cold-blooded creatures, in contrast, fungi pose grave threats. Chytrid fungi have driven more than ninety amphibian species to extinction. Ophiocordyceps camponoti-floridani, which inspired the fungus that jumps to humans in “The Last of Us,” is notorious for taking over the brains of ants, seemingly steering them away from their usual habitat and into places where the fungus can proliferate.

White-nose syndrome, a fungal disease that afflicts bats, suggests what can happen when a microbe overcomes a mammal’s thermal barrier. Bats survive the scarcity of winter by hibernating in caves; during this time, their bodies cool. The fungus that causes white nose, Pseudogymnoascus destructans, thrives between fifty and sixty degrees. It starts to grow on bats’ muzzles, ears, and wings while they are hibernating, often causing them to emerge from hibernation early and starve to death. “By the time you get to our temperature, you can keep out ninety-five per cent of fungal species,” Casadevall told me. But in recent decades he has grown concerned that, in a fluctuating climate, fungi could jump the thermal barrier that protects humans.

A relatively small number of fungal diseases already afflict us, and some of them may be spreading. Coccidioides, a soil fungus that can cause a respiratory infection called valley fever when its spores take up residence in the lungs, needs moisture and rain to grow. California, which has experienced wetter wet seasons and drier dry seasons, saw an eightfold increase in cases between 2000 and 2020. Blastomyces, another fungus that can infect the lungs, grows in moist soil and decomposing wood along riverbeds, but cold winters seem to kill it off. In Minnesota, where winters have warmed markedly, infections have quadrupled since 2000. The nation’s largest outbreak, which occurred in Michigan and afflicted a hundred and sixty-two paper-mill workers, peaked during one of the first winters in memory when the local river reportedly didn’t freeze over.

In a 2010 research paper, Casadevall predicted that climate change would encourage fungi to adapt to warming, giving them new opportunities to infect humans. Months before his paper was published, a seventy-year-old woman at Tokyo Metropolitan Geriatric Medical Center came down with a stubborn and unfamiliar infection. When doctors swabbed her ears, they found an unknown fungus that they dubbed Candida auris. (Auris is Latin for ear.) The fungus had no problem growing at a hundred and four degrees.

Casadevall hypothesized that C. auris originally afflicted plants and began to spread to humans after it developed a heat tolerance. “There is no other explanation that anybody can think of,” Casadevall said. The fungus was soon detected in patients around the world. It proved resistant to two out of three available antifungal medications, and to ammonium cleaners often used in hospitals, suggesting that efforts to kill microbes might have also helped it evolve. Infections have a mortality rate as high as sixty per cent in immunocompromised or elderly patients, whose bodies have a hard time fighting off the fungus.

One of Casadevall’s postdoctoral fellows, Daniel Smith, has documented what seems to have been fungal adaptation in real time. On a hot summer day in 2023, he smooshed yellow Starburst candies onto the sidewalk in several Baltimore neighborhoods, hoping that they would serve as a glue for microorganisms. He then dissolved the candies in saline and cultured the microbial life that had been picked up. One of his research sites was a dense city block on Fayette Street, where the sidewalk averaged a hundred and two degrees. Another was in the suburban neighborhood of Guilford, where temperatures in the shade were closer to eighty degrees.

The fungi in hotter neighborhoods turned out to show marked differences. Molds and yeasts there were lighter in color, suggesting that they were producing less melanin pigmentation, which absorbs heat. Several types of fungi were found at only the hottest sites—for example, a heat-resistant strain of a common yeast and several species of Cystobasidium, which can infect immunocompromised people. One species, Cystobasidium minutum, could grow at ninety-eight degrees. “The more the world’s conditions mimic our bodies’, the more likely fungi are able to overcome this thermal barrier that’s protected us for millions of years,” Smith told me.

In the near future, someone you know could be infected with climate-changed microbes. In 2016, Scott Lorin, the president and C.O.O. of Mount Sinai Brooklyn, in the neighborhood of Midwood, learned that three patients in his intensive-care unit had tested positive for fungus in their blood. Labs initially pointed to Candida albicans, a treatable infection that tends to afflict people with intravenous catheters, but none of the patients had one. Something’s not right, Lorin remembers thinking. A second round of tests returned a more troubling result, one that he had never seen before: Candida auris.

Lorin, an energetic physician who wears a suit as often as he wears a white coat, asked his employees to test the entire I.C.U. They were disturbed to find C. auris spores everywhere, even in places that doctors and nurses couldn’t reach: on the blinds, high up on the walls, on the ceiling. The I.C.U. had to be evacuated for three days of decontamination. The cleaning staff threw away bedding and ripped out ceiling panels.

Nowadays, patients who are most likely to test positive for C. auris—those who come from care facilities or who rely on equipment such as dialysis machines or ventilators—are swabbed on arrival. Anyone who tests positive is isolated on the second floor. In March, Lorin and several of his colleagues showed me around. We stood in a room that looked normal enough: beige walls, tile floors, an adjustable bed ringed by a curtain. This room was reserved for C. auris cases. When it’s occupied, hospital employees who enter are required to wear full-body protective suits. They even use disposable stethoscopes. Vani George, the director of infection prevention, told me that a patient in a room next door had just tested positive for C. auris that morning.

The way these rooms are disinfected between patients, Lorin said, goes “beyond any terminal clean we’ve ever done in the history of the hospital.” He and his colleagues have published their protocol, for other hospitals to follow. “Gloves, toilet paper, paper towels—everything goes in the garbage,” Ulanda Wills, one of the hospital’s cleaners, told me. “Then we sanitize the room: bleach top to bottom, the ceiling and the walls in a clockwise direction.” Sometimes it takes two or three passes before the infection-prevention team gives the all-clear.

We shuffled out of the room so that the head of the cleaning team could roll in an ultraviolet-light machine, called Space-1. Its four expandable arms emit enough UV radiation to break down microbial DNA; in two minutes, it can kill ninety-nine per cent of microorganisms. A window in the door began to glow neon blue. When the door opened again, I caught a whiff of what smelled like bleach and melted wax.

Mount Sinai Brooklyn hasn’t had a C. auris outbreak since 2018. Yet no one who works there expects to eradicate the fungus. “Once you have the C. auris colonization, you’re always colonized,” George told me. Humans are a step behind: when microbes change, all we can do is react.

One way to imagine the future of microbes is to look at their past. In March, I visited one of the world’s largest collections of ice cores, at the Ohio State University’s Byrd Polar and Climate Research Center. Scientists have long drilled cylinders of ice out of glaciers and ice sheets in search of details about Earth’s prehistory, such as ancient bubbles of air and particulates from the atmosphere. Only in the past few years did they realize that microbes were also preserved in ice cores.

After zipping into a bright-orange parka, I stepped into a vast walk-in freezer that was thirty degrees below zero. My lungs tightened and my knees tensed. Long metal tubes filled with ice, some of it from glaciers that no longer exist, were stacked on rows of shelves. “These cores come from Kilimanjaro, in Africa,” Lonnie Thompson, an O.S.U. paleoclimatologist, said, pointing to some tubes. “That’s the only collection in the world.”

Thompson has been collecting glacial ice for fifty years with his wife, Ellen, who is also a paleoclimatologist. He led me to a room where researchers examine samples—it was a mere twenty-four degrees—and slid out an ice core from Huascarán, the highest tropical mountain on Earth. “You can’t go any higher, can’t get any colder,” he said. The deepest part of the core was more than thirty thousand years old; to get it off the mountain, he’d hired forty-five skilled climbers and mountaineers, as well as a helicopter. Next, he slid out a core from the world’s oldest non-polar glacier: the Guliya ice cap, on the Tibetan Plateau. It contains ice that is at least seven hundred thousand years old. I could see tiny dust particles frozen inside.

Cartoon by Andy Friedman

Virginia Rich, a microbial ecologist at O.S.U., has studied the Guliya ice with her colleague ZhiPing Zhong, focussing on samples from cold and warm periods in the past hundred and fifty thousand years. “We see a coördinated shift in microbiota,” Rich told me outside the freezer, after we had removed our parkas. They have observed changes in the over-all diversity of microorganisms, and in which species were dominant. They can’t say what consequences these changes had—only that, when the climate shifted, microbe populations did, too. Another of Rich’s colleagues, Matthew Sullivan, found that viral communities also fluctuated with a changing climate. For Rich’s next project, she’ll study a period of rapid warming in the nineteenth century—the end of the Little Ice Age. “One of the big unknowns is how quickly the microbes today are going to be adapting,” she said. “We will be able to say, for individual microbial species, How did they respond under warm versus cold conditions within the past two hundred years?”

Down the hall, I met Brady O’Connor, a microbiologist who studies Antarctic ice cores that go back at least fifty thousand years. He and his colleagues are studying species in the ice by waking them up. He has melted ice from the center of a core and put it on petri dishes, to see what grows. The risk that the resulting microbes could infect humans or animals is very low, he told me, in part because they evolved to live in such cold temperatures. I warily examined a dish that contained two beige spots, each smaller than a dime. “We don’t have an I.D. on this one yet,” he said, gesturing toward the spots. They had appeared in the dish the week before. In the ice, the microbes had likely been dormant, doing just enough to survive in the extremely cold environment, but now they were dividing quickly. Each spot contained millions of cells.

It’s become increasingly clear that some of climate change’s greatest threats come not from warm places heating up but from cold places defrosting. In 2016, a Siberian outbreak of anthrax bacteria, which ultimately infected thousands of reindeer and at least seventy people, was attributed to thawing permafrost that had released dormant spores. More recently, an international team of researchers revived thirteen “zombie viruses,” including several that infect amoebas, from Siberian permafrost. The viruses were estimated to be hundreds of thousands of years old. O’Connor told me that, when glaciers melt, microbes in the ice flow into the ocean, with unpredictable impacts on the ecosystems they join. Decomposer microbes can break down biological materials, producing greenhouse gases such as methane, which traps twenty-eight times more heat in the atmosphere than carbon does. Photosynthesizers such as algae can bloom, producing oxygen but also choking out local species. “The microbes will be fine,” O’Connor said. “They are running the planet, and they will continue to run the planet.” It’s the rest of the ecosystem that may be affected.

Nicoletta Makowska-Zawierucha, a microbiologist at Adam Mickiewicz University, in Poland, has documented these risks in Svalbard, Norway. In samples of runoff from melting glaciers, she found plasmids—self-replicating loops of microbial DNA—that were thousands of years old, meaning that they’d never had contact with many organisms alive today. Arctic microbes are accustomed to living in extreme conditions, she told me, so they have become genetically tough. “They not only have genes with unknown functions but also genes with antibiotic resistance, metal-resistance genes, and biocide-resistance genes,” she said. Each of these genes could make the microbes more difficult to kill. For her discovery, she was a finalist for the Frontiers Planet Prize, a million-dollar environmental award.

Makowska-Zawierucha’s concern isn’t that microbes will be infectious in themselves but, rather, that their genetic material could change the wider microbial world in unforeseeable ways. Humans share genes vertically, from one generation to the next: we pass them to our children but not to our siblings or our friends. Microbes, in contrast, often share DNA through a process called horizontal gene transfer. They can release plasmids into the environment, enabling other microbes to scoop up useful genes—for example, instructions for digesting new foods, surviving antibiotic compounds, or making particular chemicals. Some bacteria even use a hairlike appendage called a pilus to physically latch onto other bacteria, then hand off fragments of their DNA. In Svalbard, which is warming at a rate four times the global average, Makowska-Zawierucha saw glacial runoff mixing with ocean water and sewage. “This is a really dangerous mechanism,” she told me. It’s impossible to predict where the microbial DNA will end up.

Perhaps microbes could help clean up the messes that we humans have made. Some scientists dream of capturing carbon in microbial bioreactors, or of cultivating microbes that eat methane or plastic; certain soil microbes could make crops more tolerant to drought or to heat. Raquel Peixoto, a marine scientist at King Abdullah University of Science and Technology, in Saudi Arabia, has studied microbes that help corals survive in the Red Sea. Her research suggests that beneficial microbes could be transplanted onto coral reefs during heat waves, making the corals less vulnerable to bleaching and death. “You have to restore the microbiome first,” Peixoto said. “I don’t see a future without us doing that. It starts from microbes.” Microbial interventions will have to be screened for safety, Peixoto and colleagues wrote in a recent Nature paper. Humans are just beginning to understand how microbes shape the environment, and there could be unintended consequences of trying to harness their powers.

Last year, the International Union for Conservation of Nature, which has traditionally worked to protect endangered plants and animals, formed its first group dedicated to cataloguing and preserving the world’s microbes, recognizing them as life-forms worth saving. It will create a list of endangered microbes and where they live, and also encourage the collection of rare microbes that inhabit extreme environments such as deserts or the deep ocean. A similar effort, the Microbiota Vault, will preserve microbe species from our food supply and our digestive systems. Groups from Benin, Brazil, Ethiopia, Ghana, Laos, Thailand, and Switzerland are collecting almost two hundred fermented-food samples and more than a thousand human fecal specimens. The effort is inspired by the Svalbard Global Seed Vault, which preserves thousands of species of plants: if planetary conditions change so much that a microbe disappears in the wild, humans will have a chance to bring it back.

But the sheer scale of how much microbial surveillance is needed is hard to fathom. The recently created Microbe Atlas Project uses data from more than fifty thousand studies to make a map of the planet’s microbiome. But the database would need to grow by orders of magnitude for it to encompass all the microbial species that are thought to exist. Eren, the computer scientist, argues that environmental microbes should be sampled around the world daily, in the same way that the National Oceanic and Atmospheric Administration gathers weather data. “People want to manage and protect the environment, but the entity doing most of the actual biological work on the planet is evolving out from under our control and management frameworks in real time,” he said.

During my trip to Maryland to visit Spear, I also met with Henry Sage, one of Rita Colwell’s Ph.D. students at the University of Maryland, in College Park. We walked down to a tributary of the Paint Branch River, which runs along campus, and Sage delicately balanced on stones in the riverbed so that he could gather water samples. The river gurgled innocently, sunlight reflecting off its surface. It was a peaceful setting, not one that seemed dangerous at all.

Afterward, Sage e-mailed me to say that the water appeared to contain small quantities of Vibrio cholerae, the bacteria that cause cholera. Sage will devote almost all his Ph.D. research to monitoring the Potomac River for just one family of microbes. After reading his e-mail, I thought about the billions of microbial species on Earth that are undergoing transformations, and the number of scientists who would be needed simply to understand what’s happening to them.

In the spring, Spear called me to check in. Nine months after his infection, he was finally done with medical treatment. He texted me a picture of his arm: the transplanted skin was slightly pinker than the rest, and I could see a pink splotch on his leg, but otherwise he had healed remarkably well. He was still wary of going back out to the water, but he thought that might change. He’d been researching a pair of protective rubber gloves that are often used for muskrat hunting. “When the weather gets warm again, I’m going to want some crabs,” he said, laughing.

On one of my evenings in Maryland, I stopped by the Inner Harbor, in Baltimore, to get some dinner. The sun was setting, and it was warm enough that I wanted to eat outside. Perhaps I’d even try blue crab. As I got out of my Uber, though, I caught a whiff of something pungent that I’d noticed earlier in the day. The closer I got to the water, the more the air smelled of decay. I asked a restaurant hostess what was going on, and she told me that the harbor had recently experienced what’s known as a pistachio tide. After an unseasonable autumn heat wave, oxygen-rich surface water had cooled quickly, increasing its density and causing it to sink. The water at the bottom of the harbor, which is low in oxygen and rich in sulfur-eating bacteria, had risen to the surface. Thousands of fish, shrimp, and crabs had suffocated, and the sulfur bacteria had multiplied, turning the harbor neon green. In the end, I went back to my hotel room with takeout. I closed the window tightly. I could still taste the rot in the air. ♦