It’s been chilly in the Catskills, where our family lives. The chickens are under threat of frostbite, the dog has to be pushed outside, and our jeans are bulky from long underwear; the weather app shows negative numbers in the evenings. Cold is something we are subject to—it hurts, and all we can do is dress for it. I can’t prevent the storm that encases my car in ice any more than I can disperse the sticky air of a subway station in July.
And yet hints of another world push back against the cold. In 1981, Herbert Benson, then a physician at Harvard Medical School, travelled to the Himalayas to take the temperatures of three Buddhist monks. The monks had been living in near-solitude for nearly a decade, in small stone huts without heat or insulation at elevations of six thousand feet or higher; they’d been practicing g-tummo, a secret meditation technique, every day for several years. Benson attached disk thermometers to several parts of each monk’s body, during meditation or afterward. In a study published in the prestigious journal Nature, he reported that, while meditating, the monks could increase the temperature in their fingers and toes by up to seventeen degrees Fahrenheit. Scientists had previously documented the possibility of a person heating her own extremities using biofeedback, but those temperature increases had been slight. Here was evidence that a person could be his own furnace.
A few years later, Russ Pariseau, a documentary filmmaker who was covering Benson’s research, stood behind his camera in a prayer room in Manali, Himachal Pradesh, in India. The room was cold, about forty degrees. A group of monks wearing only undergarments sat on the floor, along with a few buckets of cool water. As Pariseau’s camera rolled, the monks dipped thin white sheets in the buckets, then draped the wet sheets around their backs and shoulders. They began g-tummo. In an e-mail, Pariseau recalled that he soon noticed “vapor rising from bodies all around.” The room began “noticeably warming up.” The event was a friendly competition among advanced students to see who could dry the greatest number of sheets—“something like a championship tournament.” On another winter night, Pariseau witnessed several monks sleeping on a stone ledge somewhere between the Himalayan and Karakoram mountains. “I was dressed in layers of down but still uncomfortably cold,” he said. The monks were wearing thin shawls of wool or cotton.
Maria Kozhevnikov, a neuroscientist at the National University of Singapore and Massachusetts General Hospital who also holds an appointment in radiology at Harvard Medical School, wasn’t that impressed by Benson’s study. The steaming sheets, she figured, were just the physics of water hitting cold air—like seeing your breath on a frigid day. And what was so special about heating up one’s digits? “It’s not unusual,” she told me. “Anyone can imagine putting their fingers into warm water and eventually the peripheral body temperature could be increased.”
Kozhevnikov wanted to know if the monks could raise their core body temperatures. That’s a harder problem: maintaining an internal temperature of 98.6 degrees is more or less a requirement of having a human body on Earth. She travelled to Nangchen town, in the Amdo region of Tibet, an area known for g-tummo practice. There, she took the core body temperatures of several monks and nuns during meditation. It was January, and even inside the house where she ran the experiment the temperature hovered between thirty-two and thirty-six degrees. Kozhevnikov taped disk thermometers to the meditators’ armpits, attaching them to a computer, which allowed her to obtain readings without being in the room with the nuns. Her skepticism changed to awe as she watched the data emerge. “It was amazing,” she said. “You see the core body temperature change.” It wasn’t just that they increased their core body temperature; aerobic exercise can do that, too. It was that the meditators gave themselves fevers. At least one monk raised his body temperature from 98.6 degrees to 100.8.
In Kozhevnikov’s report, published with some colleagues in the journal PLOS One, she explains that g-tummo involves a breathing technique called “the vase,” in which meditators contract their abdominal and pelvic muscles. They picture a flame rising from below the navel to the top of the head. I asked Kozhevnikov if she could share more about how g-tummo is done; she told me that she’d agreed to keep the practice confidential as a condition of her visit. “They visualize the spine being on fire,” she said. G-tummo meditation, she went on, is not a state of relaxation but arousal. She thinks it may increase blood flow to the brain. G-tummo is difficult, requiring years of dedication to master. As I contemplated whether it could help me cope with the cold, it occurred to me that using this sacred technique to avoid discomfort might not be in line with its origins in Buddhism, a religion in which suffering is acknowledged and accepted. Kozhevnikov thinks that it could be useful for pilots and astronauts who run the risk of losing consciousness during acceleration; for the average cold-averse person, though, she suggested sticking to the imagination. Try “visualizing your fingers in hot water, or yourself in a hot environment,” she said. It might not raise your core body temperature, but it could make you cozier.
Meditation and visualization aren’t the only ways to self-generate heat. Anger makes us hot under the collar. Romantic crushes make us sweaty. The same is true for embarrassment, and for menopause. Clearly there are mechanisms in our bodies designed to heat us up, either as a goal or a side effect, and there is a tight link between our behavior and our temperature. Most of the research seeking to understand why our cheeks start burning when we trip on the sidewalk involves the fight-or-flight response. The release of adrenaline triggered by such moments gives us a burst of survival-driven energy, and that’s accompanied by a surge of heat.
Could the process be reverse-engineered? Could we force a bout of heat-inducing anger that blunts a brutal wind chill? If you wanted to do that, you’d first need a map showing which body parts heat up in response to which kinds of thoughts. In fact, we have the technology to create such a map, courtesy of the U.S. military. Modern soldiers find people in the dark using thermal imagery, which detects heat radiated by the human body; as soon as the technology was declassified, in 1992, it became available for psychological experiments.
Emilio Gómez Milán, a research psychologist at the University of Granada, in Spain, has conducted several psycho-thermal studies. In 2018, he and some colleagues told ten psychology students that they were part of a top-secret research program, and that they needed to call a friend or relative and lie about their current whereabouts. A control group were asked to make similar phone calls, but were allowed to reveal that, in fact, they were part of an experiment. Using thermal imagery, the researchers found that the noses of seven lying students grew hotter by two degrees before the calls, while they were crafting their alibis; during the calls themselves, nose temperatures among eight students dropped by two degrees. Forehead temperature also increased during the planning stage—and then, for six of the students, increased again during the telling of the lie itself. Gómez Milán and his colleagues speculated about the warming and cooling. Perhaps the initial nose and forehead warming could be attributed to the anxiety of planning to lie, and the subsequent forehead warming to the mental workload of maintaining the ruse; after the lying was finished, anxiety lessened, along with facial temperatures. In the end, changes in nose and forehead temperature enabled the researchers to determine liars with eighty-five per cent accuracy. This “Pinocchio effect,” as Gómez Milán calls it, may be connected to hypothalamus activation, and also to the insula, a part of the brain’s reward system which is activated by emotions and involved in regulating body temperature.
In the name of psycho-thermal research, Gómez Milán has put study volunteers into tense imaginary situations. He has asked them to decide whether they’d call the police on a loved one suspected of having terrorist ties, whether to pay a ransom to free a journalist being tortured by the Taliban, and whether U.S. soldiers should stop or continue the torture of an Islamic terrorist who may have information about a forthcoming attack in Spain. In all these studies, temperatures shifted in specific ways related to emotion and calculation. “In economic dilemmas hot decisions are the emotional ones and cold decisions are the rational ones,” Gómez Milán told me. When the sympathetic nervous system prepares us to deal with an emergency—stopping the torture, for example—nose temperature decreases. As the parasympathetic system takes over and we calm down, nose temperature tends to rise. Yet the effects vary depending on whether a person is already in a state of arousal or relaxation. The effects are complicated. Passion can make a nose cold; tenderness can make it warm; mental fatigue heats the forehead and cools the nose. All this may not be very helpful as you wait for a bus on a cold night.
Enough already, you might say—there are four seasons, and you must live with them. There’s a lot of pressure to embrace the cold. The Dutch athlete Wim Hof, a.k.a. the Iceman, plunges into icy water with a tolerance that makes him just as awe-inspiring as the self-heating monks; he argues that this exposure, combined with a breathing technique that helps him withstand extreme cold, has enabled his immune system to resist serious bacterial infections. There is some evidence to support this claim. In one study, mice that have been genetically engineered to have reduced body temperatures lived longer than non-mutated mice. Some research has suggested that cold showers ward off depressive symptoms.
I prefer to model my own defense mechanisms on certain honeybees who, when faced with a dangerous giant hornet, swarm around it to create what scientists call a “hot defensive bee ball.” They beat their wings until the air heats so much that it kills the invader. The unity here is inspiring, and so is the amount of heat generated just by being together. I’m also a fan of the Arctic ground squirrel: in Alaska, these rodents, which can weigh just a pound and look like tiny-eared mice covered in lush fur, begin hibernating in late summer. In the days before they hunker down, their little mouths are stained blue from gorging on enough wild berries to double their weight; they go into their underground nests, plug up the entrances, flop their tails over their heads, and stay that way for several months, during which nearly all of their bodily reactions stop.
A few decades ago, Brian Barnes, a zoophysiologist at the University of Alaska Fairbanks, began trapping Arctic ground squirrels so that he could study their hibernation habits. He also started sticking thermometers into their burrows. He discovered that their body temperatures can plummet to 26.5 degrees Fahrenheit. “That turned out to be a world record,” he told me; no other warm-blooded mammal gets quite that cold. The ability is puzzling, since, like people, Arctic ground squirrels contain a lot of water. How do they survive life below the freezing point? “They’re spending half their lives at a body temperature lower than that of an ice cube, and that’s normal for them,” Barnes said. It turns out that, instead of turning to ice crystals, the water inside the squirrels becomes a supercooled liquid. The animals filter their own bloodstreams, removing particles that might help water turn into ice (dust and pollen play this role on plant surfaces); this enables their blood to keep flowing even at temperatures below freezing. “Think ice-rimmed streams,” Barnes suggested. “It’s quite spectacular.”
A southern Californian transplanted to Alaska, Barnes has spent his entire career studying animals that survive extreme cold. Hibernation isn’t sleep, he explained. Instead, it’s a state of “deep torpor.” The brain is active just enough to keep the animal’s heart and lungs operating. Torporous animals are far less responsive than sleeping ones. In the nineteen-sixties, one researcher removed several golden-mantled ground squirrels from their hibernation nests, tossed them in the air, and put them back; the animals stirred briefly during the event but returned to torpor within a day. He took the squirrels from their nests a second time and tossed them in the air again. This time, the animals only sometimes stirred, and their brain temperatures remained near forty degrees the whole time. Having learned that the sensation posed no threat, they stayed in torpor—some through a hundred throws.