THIS PAST AUTUMN, beneath the smoke of wildfires across northern California, came reports of nosebleeds and coughs. Worsened asthma and bronchitis and pulmonary disease. In Oakland, hardware stores sold out of particulate masks. In Houston after Harvey, in the Virgin Islands after Irma, in Puerto Rico after Maria. Drownings and algae blooms and floating colonies of fire ants. In New Jersey after Sandy, in New Orleans after Katrina. Power outages and sewage overflows: outbreaks of cholera, of hepatitis A, of ringworm and scabies. In Texas, a young carpenter repairing homes was killed by necrotizing fasciitis, a flesh-eating bacteria. “Most likely, this person’s infection occurred when bacteria from Harvey debris or floodwater entered his body through a wound or cut,” an infectious disease specialist told the New York Times. It was the second such death in Houston.

As an ecosystem changes, so do its threats. The deer tick season in North America is lengthening; so is mosquito season. So is pollen season. Insects that breed more rapidly, and fly more distantly, bring dengue, malaria, Lyme disease, West Nile. Ragweed grows taller and produces more allergens when exposed to more carbon dioxide. Declining air quality brings respiratory illnesses, then complications, the kind doctors call “acute on chronic,” in which a persistent condition becomes suddenly inflamed. Declining water quality brings leptospirosis. In warming lakes and oceans grow noxious microbes with Latin names conjuring the primordial predators they are: Naegleria fowleri, Vibrio parahaemolyticus.

In 2016, the US Global Change Research program, a nonpartisan body, published a report titled “The Impact of Climate Change on Human Health in the United States: A Scientific Assessment.” Its authors included experts from the Centers for Disease Control (CDC), the National Institutes of Health (NIH), the Environmental Protection Agency (EPA), and the National Oceanic and Atmospheric Administration (NOAA). Its more than three hundred pages contained maps of flood and drought, tables of asthma statistics, graphs of premature deaths in America from extremes in summer heat and winter cold. “Climate change is a significant threat to the health of the American people,” it concluded. “Every American is vulnerable.”

Until recently, however, most organizing bodies of physicians remained quiet on the issue of climate change. Such silence is a problem, a growing community of doctors has begun to argue. “There’s been a gross abnegation of our responsibilities,” said Dr. Stuart Harris, of Massachusetts General Hospital (MGH) in Boston. “As a physician, you are charged to advocate for a rational understanding of science, to put that into a meaningful narrative about how it impacts our patient population. We have failed at that, as a specialty and as a profession. We should be embarrassed.”

Harris is not alone in feeling this way. “Where are the physicians, weighing in on health impacts?” one of his colleagues, Dr. Tracy Cushing, asked me. “There was a conspicuous absence. We’re doctors. It’s a health issue. The sooner we can deal with that, the sooner we can start articulating solutions.”

On a recent Sunday, I accompanied Harris on a shift in the emergency department at MGH. It was an unseasonably warm morning for late October in New England: by the time his seven a.m. shift began, it was already sixty degrees. Inside the warren of the hospital, all was brightly active, noisy with chatter and beeping machines, lit by EKG monitors and digital displays like the departures screens at airports. Harris, who is fifty, with a neatly graying beard and small Nike eyeglasses, speed walked amiably through hallways, patting colleagues on the shoulder, slipping in and out of examination rooms, slathering his hands with sanitizer from wall dispensers as he went. Then he retreated to a bank of computers alongside the dozen-odd residents and nurses he oversaw to slip his feet out of his shoes and file patient reports. Every few minutes, someone interrupted him — either with a question, update, or request about some diagnosis, test order, or discharge plan, or to drop paperwork on his workstation for him to initial. Each time, Harris listened politely, and gently asked clarifying questions: “Are you worried about his subdiaphoretic process?” Or, if he approved: “Beautiful!” Every so often, another patient was wheeled past in a gurney.

Periodically Harris stood and hustled to another examination room, or for another lap around the wing, and I had to rush to keep pace. With the patients themselves, at the privacy of their bedsides, he was calmly attentive, as though each room were a tiny oasis. One elderly woman who seemed to suffer from dementia started to relay a sequence of symptoms that, though I tried, I found impossible to follow. Then she stopped short. “I don’t want to waste your time,” she said to Harris. “I know you’re busy.” Harris, his hands folded over the rails of her cot, shook his head gently. “My time is yours,” he said. “You’re the only reason I’m here.” Minutes later, in a different room, he was chatting with a serviceman from the Navy who had fallen down a flight of stairs. Then he was asking a widow with shortness of breath about the mining company her late husband had owned.

Harris has been at MGH for almost two decades, since he arrived from the Medical College of Virginia in 1999 to train in emergency medicine. He was especially interested in hypoxia.

As a serious mountain climber, his interest was partly an excuse to return to Everest. But the ailment also fascinated him, particularly in how relevant it was to so many other conditions. Hypoxia simply meant a lack of oxygen, and oxygen mattered for everything. “A heart attack is just a lack of oxygen to the heart muscles,” he told me. “A stroke is just a lack of oxygen to the brain.” To study hypoxia was to study a cause or effect of many diseases and disorders. Strangers often wondered why a physician in a city, at sea level, would study diseases of altitude, but in fact Boston was an ideal place to study those things. “If you’re already in Denver, your subjects are acclimatized,” he said. “It’s not helpful. You’re not learning anything. It’s a terrible place to study altitude illness.” In Boston, on the other hand, he could put a patient into a chamber to simulate any altitude he wanted. When MGH invited him to stay, Harris didn’t hesitate.

Today, Harris’s specialty is the broader field of wilderness medicine, which is defined by the Wilderness Medical Society as “the practice of medicine where definitive care is more than one hour away . . . defined by difficult patient access, limited equipment, and environmental extremes.” Originally, the field was conceived for isolated regions: on glaciers and cliff sides, in forests and deserts. Increasingly, with our changing climate, it is becoming relevant even in cities. A principle of the discipline is in improvising capably no matter the setting. This is useful not only above a treeline or inside a canyon, but also after droughts and tornadoes, after earthquakes and avalanches, after wildfires. “Hospitals weren’t built as a prison to keep doctors in,” Harris explained. “They ought to be looked at as a runway from which a well-trained doctor can take off and go anywhere in the world, appropriately trained and equipped, and provide excellent medical care.”

An example was Haiti, after an earthquake in 2010. “What we saw after Haiti is that thousands of variously trained medical providers showed up from all over the world,” Harris recalled. “They didn’t know how to take care of themselves first. They didn’t know how to get clean water, how to dispose of their waste, how to stay dry. They quickly became burdens on the overall system. It wasn’t even that they were not providing care. They were a net negative.”

A separate field of care, called disaster medicine, existed already for the aftermath of an event like Haiti’s earthquake, and its providers do terrific work, Harris said — “but usually with a gigantic footprint.” They need trucks, helicopters, generators, support staff. Often, they coordinate with the military or with large nongovernmental organizations. Wilderness medicine, on the other hand, typically involves just a single provider. Because these doctors can travel more lightly, they can travel more quickly, and in a wider range of settings. Certain crises are better suited for one discipline or the other.

In 2003, Harris persuaded MGH to found its own division of wilderness medicine, the second in the country behind Stanford University. It comprises a trio of research, teaching, and clinical care. In weekly or biweekly classes, Harris leads residents and medical students through textbook lessons on plant toxicology and volcanic eruptions, on wilderness orthopedics and crocodile attacks. It happens that physicians drawn to the specialty often care for the outdoors and are the sort of people who sideline as environmentalists, whose sense of adventure compels them into the Yukon or the Arctic or the Great Barrier Reef — where ice is melting, where coral is bleaching, where migratory patterns are shifting. Harris himself grew up amid the rivers and lakes of the Blue Ridge Mountains. His grandparents met while building what would become the Appalachian Trail. A person like this is predisposed to understand the planet as both robust and fragile, to understand that a distinction between human and global health is virtually meaningless. Soon, Harris’s residents were carrying portable ultrasounds into the field. These were lightweight, their energy demands modest, and they could be used quickly and almost anywhere to examine ankle fractures or orbital veins. The division offered a monthlong course each spring called “Medicine in the Wild,” taught in the Gila Wilderness of New Mexico. In 2008, it added a post-residency fellowship. It collaborated with the National Outdoor Leadership School and with The Polaris Project, a group that monitors climate change by ushering young scientists to frozen settings to examine the thawing Arctic permafrost. In 2009, army physiologists sought Harris out to predict how American soldiers might acclimate to the peaks of Afghanistan.

“When I came out of residency, there were no wilderness fellowships in the country,” Harris said. Now there are more than a dozen. Programs like the one at MGH have emerged at Cornell and Johns Hopkins, at the universities of Colorado and Utah. At Yale, a yearlong program grants a diploma in Mountain Medicine. The American College of Emergency Physicians now sponsors a section — an interest group — on the topic. Fellows from MGH and elsewhere have gone on to work with the Himalayan Rescue Association and with climbing ranger patrols at Denali National Park. They have treated patients in Antarctica, on the Mekong Delta, and on Hopi reservations. They work after bear attacks and snakebites, after lightning strikes and avalanches, with only the barest modern essentials of equipment and technology. Most are primarily emergency physicians, but not all: the incoming president of the Wilderness Medical Society is an orthopedic surgeon.

Meanwhile, as the field of wilderness medicine was gaining traction in remote areas, people like Harris starting applying the backcountry curriculum in cities. “It can be in a true wilderness area,” Harris told me, of where his colleagues saw demand. “But it can also be in New York City after Sandy. It can be along the coast of Japan after the tsunami in 2011. It can be in the daily course of business throughout the developing world.” Wilderness in this context is more than a setting. It is a method. In a bare locale, without labs, screens, or imaging, or in a city after electricity loss, a doctor must learn to provide in the absence of these tools.

“Increasingly, even here — and it drives me nuts — people are wheeling around with their computers,” Harris complained, gesturing around the emergency department. “The computer is literally between them and their patient. The patient is talking to them and you’ll see people typing away.” Sure enough, more than one doctor was perched inseparably from a monitor and keyboard, wheeling it between rooms and through hallways. Earlier that morning I’d seen a young doctor check the pupils of an unconscious patient by shining an iPhone flashlight into his eyes. Inside a well-resourced hospital, those dependencies seemed modest. The technologies are available, so doctors make use of them. But it is easy to imagine that a physician with such habits might strain in leaner circumstances.

All morning, as I listened to doctors, nurses, and patients speak with one another, it surprised me to notice how often their rendering of the same emergency might conflict. A patient would give more than one explanation for his symptoms, and the explanations wouldn’t match. Or the recollection of a paramedic would contradict a phone call from primary care. Or a relative of a patient would offer a story that no one felt certain of. This was difficult enough on a weekend at a premier hospital. I could see how much worse it might be in the confusion of a hurricane, and how necessary the independence for which Harris was advocating. This was why he asked each new patient for his or her own story directly, regardless of whether he’d been briefed already: it was so he could triangulate information and make his own judgments. As he put it, “To be able to take a good history is critical, the diagnostic engine of medicine.” Careful listening and decision-making, he told me, are among the highest priorities of wilderness training.

Just before two p.m., as Harris filed patient reports, static blared from mounted radios and the crackling voice of a paramedic filled the room, surrounded by the wash of sirens and street noise. Everyone stopped what they were doing to listen. It was the quietest I’d seen the place all shift. A handful of doctors and nurses abandoned their workstations to prepare a room in anticipation. Soon, a man was wheeled in briskly by shouting paramedics. A heart attack. Paramedics had been forced to shock him three times inside the ambulance and to inject epinephrine. Now he was breathing shallowly, but he hadn’t regained consciousness. A dozen bodies filled the room and a curtain was drawn: quickly, the man was stripped, intubated, plugged into machines by a spill of tubes and wires. A bag valve obscured his face and a heart monitor was clipped to his toe. A technician wheeled in a mobile X-ray machine as large as several men. Nonetheless, doctors struggled to gauge the man’s vital signs. Data from his lungs wasn’t registering. Possibly this signaled a problem, they murmured. Or else the equipment had simply malfunctioned. Either his lungs were in trouble or a machine was. Doctors needed to know now. But they weren’t certain. Harris had slipped out to speak briefly with the man’s wife, but presently he returned, and the residents shared their dilemma. What should they do?

Moments later Harris left again, and this time I followed. “People ask, ‘Why wilderness medicine in the heart of Boston? You’re not in the Amazon, you’re not on Kilimanjaro,’” he said. Then he turned and nodded back to the examination room, where more doctors continued to work. “It comes to you.”

THE definitive textbook of wilderness medicine is aptly titled Wilderness Medicine. It was edited by Dr. Paul S. Auerbach, an emergency physician at Stanford and cofounder of the Wilderness Medical Society. Currently, the textbook is in its seventh edition. Harris recently became a coeditor, as did Cushing, the first wilderness fellow to graduate from MGH.

Auerbach was an early proponent of physicians speaking up about the harm that a degraded climate is doing to their patients. In a 2008 article in the Journal of the American Medical Association, he urged fellow healthcare providers to assume a leadership role in popular understanding of, and education about, what amounts to an issue of public health. An injured planet isn’t inventing new maladies, but it is worsening them, and expanding their dominion, Auerbach argued. “Environmental conditions contribute to the presence or intensity of many medical conditions,” he wrote. This meant those conditions were “worthy of physicians’ attention and understanding.” Given what was happening to their patients — injury or death in cyclones and tsunamis, famine or dehydration from flood and drought, infection by mosquitoes and ticks, epidemics of asthma and allergies — his colleagues’ focus on “pathogens and disease . . . may be misguided compared with the potential loss of life that may result from such environmental eventualities as the melting of the polar ice caps.” He was calling for medical schools to adopt curricula to address “the relationship of environmental issues to human health,” as well as for medical societies and research institutes to help curate and broadcast their best understanding of what is befalling the planet. He was further encouraging his colleagues to “become more environmentally aware,” and to investigate how their own hospitals or facilities might be made more environmentally friendly so as to mitigate their harm to the root cause.

When I phoned Auerbach, much of Puerto Rico was still without electricity because of Hurricane Maria, and wildfires were still forcing evacuations across northern California, not far from Stanford, where Auerbach works. He told me that this year, the fire season in his state was already eighty days longer than usual. “This is going to be the new norm,” he warned.

Auerbach was not the first physician to suggest that his profession has something at stake in a depleted ecosystem. But he believed early on, as he continues to today, that many of his colleagues are “not sufficiently engaged in the issue.” It is incumbent upon every physician to help plot a responsible way forward, Auerbach said; “We owe it to our children and future generations to face this issue head-on.” That his own specialty is implicated is obvious: “If we don’t have a wilderness, it’s going to be hard to have a Wilderness Medical Society. We want to help start a movement.”

Recently, Auerbach, in collaboration with Dr. Jay Lemery, chief of wilderness and environmental medicine at the

University of Colorado, published Enviromedics, a book whose title the pair coined to mean “the effects, consequences, and study of the impacts of environmental change upon human health.” Intended for laypeople rather than physicians or environmentalists, the book deals not with the causes of an inhospitable planet but rather with the “medical implications” of its inhospitality. “We are neither environmental experts nor economists,” the book reads. “We are doctors on the front line who every day see medical repercussions on human beings of climate change. . . . We are convinced that drought, floods, hurricanes, toxic waste, forest fires, severe tornadoes, and pollution-filled air make people sick, or worse.”

Their case is persuasive. Physicians have “an obligation to seek remedies,” the pair argues, yet the medical community as they observe it “is not yet in a leadership position.”

The treatment of climate change as a public health crisis is not entirely without precedent, Auerbach and Lemery suggest. Consider tobacco. In 1965, according to the CDC, 42 percent of American adults smoked cigarettes. Today, less than 17 percent do. This decline over time is not accidental. What occurred in the interim was a shift in public opinion — rather, in public understanding — bolstered by physicians’ deliberate, pointed sharing of medical science. A similarly instructive effort occurred in 1980, when a collective of Soviet and American doctors joined to found the International Physicians for the Prevention of Nuclear War (IPPNW). A “clinical assessment” the group issued was plain: “Nuclear war would be the final epidemic . . . there would be no cure and no meaningful medical response.” By the fall of the Berlin Wall in 1989, the IPPNW had more than two thousand members, and “played an instrumental role in promoting international agreements to ban nuclear test explosions and close nuclear weapons testing sites and production facilities,” Auerbach and Lemery write. The physicians did so “in the face of dissonance from multiple sources, including governments, lobbyists, and political entities. Their position was unconditional and clear — the health risks of nuclear war were massive and irrevocable.” In 1985, the IPPNW won the Nobel Peace Prize.

The threat to public health from climate change may be more gradual than from nuclear war, but it is no less grave. “You wear a white coat,” Lemery told me, to explain the responsibility he feels. “You have an incredible amount of influence.” At the University of Colorado, he oversees a novel Climate & Health Science Policy Fellowship that embeds physicians within the NIH and the CDC, where they might shape the outlook of more than their own hospitals. Many of his colleagues in the medical community, he added, feel “tentative” or “nervous about getting into a political issue.” This is a shame, he says. “This should not be politicized. This is about public health. We owe it to our patients to shine a flashlight on it.”

Cushing, that first wilderness fellow from MGH, told me the culture of medical training has likely contributed to health care providers’ slow reckoning with the issue. “The house of medicine has been designed to treat disease rather than prevent it,” she said. “I don’t know too many doctors who’ve been taught to think, ‘Maybe this person’s asthma is worsened because of where she lives.’ We just prescribe an inhaler.” Obviously, ad hoc prescriptions will prove insufficient. “There’s incontrovertible evidence that an unhealthy environment leads to unhealthy people,” Cushing said. “It’s the great challenge of our time as physicians, as providers, and as human beings.”

Cushing and the others believe a more substantive approach would be for physicians to volunteer their authority, publicly and responsibly, within the boundaries of their expertise. The issue of climate change is relevant to a suite of political debates, from jobs to oil pipelines to energy policy. Not every one of those falls equally within a doctor’s purview, Lemery acknowledged. He and his colleagues might well contribute to the national discourse on some more than others. “But,” he added, “at least now we have an honest medical assessment.”

The engagement that he, Cushing, Harris, Auerbach, and like-minded doctors imagine will require physicians across disciplines. Wilderness medicine must be in the vanguard. It cannot represent the entire coalition.

The day after my visit to Harris at MGH, The Lancet, a major scientific journal, released a new report in collaboration with two dozen academic and intergovernmental organizations. “The human symptoms of climate change are unequivocal,” it read. A “delayed response . . . has jeopardised human life and livelihoods . . . [T]he voice of the health profession is essential.” Reading through its conclusions, I recalled something Harris had told me the day before: that he is a citizen before he is a doctor, and that it is possible to be political without being partisan. Not just possible — necessary. “We’re witnessing one of the biggest, most insidious degradations of ecosystems on our planet,” Lemery agreed, when I spoke to him about the Lancet report. In a few months, he would attend a conference sponsored by the Medical Society Consortium on Climate & Health. Slowly, in these reports and conferences, a movement was gaining traction. “Who’s going to own this topic? It really should be us,” Lemery said. “No one else has the mandate that we do.” O