When your Jeep spins lazily off the mountain road and slams backward into a snowbank, you don’t worry immediately about the cold. Your first thought is that you’ve just dented your bumper. Your second is that you’ve failed to bring a shovel. Your third is that you’ll be late for dinner. Friends are expecting you at their cabin around eight for a moonlight ski, a late dinner, a sauna. Nothing can keep you from that.
Driving out of town, defroster roaring, you barely noted the bank thermometer on the town square: minus 27 degrees at 6:36. The radio weather report warned of a deep mass of arctic air settling over the region. The man who took your money at the Conoco station shook his head at the register and said he wouldn’t be going anywhere tonight if he were you. You smiled. A little chill never hurt anybody with enough fleece and a good four-wheel-drive.
But now you’re stuck. Jamming the gearshift into low, you try to muscle out of the drift. The tires whine on ice-slicked snow as headlights dance on the curtain of frosted firs across the road. Shoving the lever back into park, you shoulder open the door and step from your heated capsule. Cold slaps your naked face, squeezes tears from your eyes.
You check your watch: 7:18. You consult your map: A thin, switchbacking line snakes up the mountain to the penciled square that marks the cabin.
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Breath rolls from you in short frosted puffs. The Jeep lies cocked sideways in the snowbank like an empty turtle shell. You think of firelight and saunas and warm food and wine. You look again at the map. It’s maybe five or six miles more to that penciled square. You run that far every day before breakfast. You’ll just put on your skis. No problem.
There is no precise core temperature at which the human body perishes from cold. At Dachau’s cold-water immersion baths, Nazi doctors calculated death to arrive at around 77 degrees Fahrenheit. The lowest recorded core temperature in a surviving adult is 60.8 degrees. For a child it’s lower: In 1994, a two-year-old girl in Saskatchewan wandered out of her house into a minus-40 night. She was found near her doorstep the next morning, limbs frozen solid, her core temperature 57 degrees. She lived.
Others are less fortunate, even in much milder conditions. One of Europe’s worst weather disasters occurred during a 1964 competitive walk on a windy, rainy English moor; three of the racers died from hypothermia, though temperatures never fell below freezing and ranged as high as 45.
But for all scientists and statisticians now know of freezing and its physiology, no one can yet predict exactly how quickly and in whom hypothermia will strike and whether it will kill when it does. The cold remains a mystery, more prone to fell men than women, more lethal to the thin and well muscled than to those with avoirdupois, and least forgiving to the arrogant and the unaware.
The process begins even before you leave the car, when you remove your gloves to squeeze a loose bail back into one of your ski bindings. The freezing metal bites your flesh. Your skin temperature drops.
Within a few seconds, the palms of your hands are a chilly, painful 60 degrees. Instinctively, the web of surface capillaries on your hands constrict, sending blood coursing away from your skin and deeper into your torso. Your body is allowing your fingers to chill in order to keep its vital organs warm.
You replace your gloves, noticing only that your fingers have numbed slightly. Then you kick boots into bindings and start up the road.
Were you a Norwegian fisherman or Inuit hunter, both of whom frequently work gloveless in the cold, your chilled hands would open their surface capillaries periodically to allow surges of warm blood to pass into them and maintain their flexibility. This phenomenon, known as the hunter’s response, can elevate a 35-degree skin temperature to 50 degrees within seven or eight minutes.
Other human adaptations to the cold are more mysterious. Tibetan Buddhist monks can raise the skin temperature of their hands and feet by 15 degrees through meditation. Australian aborigines, who once slept on the ground, unclothed, on near-freezing nights, would slip into a light hypothermic state, suppressing shivering until the rising sun rewarmed them.
You have no such defenses, having spent your days at a keyboard in a climate-controlled office. Only after about ten minutes of hard climbing, as your body temperature rises, does blood start seeping back into your fingers. Sweat trickles down your sternum and spine.
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By now you’ve left the road and decided to shortcut up the forested mountainside to the road’s next switchback. Treading slowly through deep, soft snow as the full moon hefts over a spiny ridgetop, throwing silvery bands of moonlight and shadow, you think your friends were right: It’s a beautiful night for skiing though you admit, feeling the minus-30 air bite at your face, it’s also cold.
After an hour, there’s still no sign of the switchback, and you’ve begun to worry. You pause to check the map. At this moment, your core temperature reaches its high: 100.8. Climbing in deep snow, you’ve generated nearly ten times as much body heat as you do when you are resting.
As you step around to orient map to forest, you hear a metallic pop. You look down. The loose bail has disappeared from your binding. You lift your foot and your ski falls from your boot.
You twist on your flashlight, and its cold-weakened batteries throw a yellowish circle in the snow. It’s right around here somewhere, you think, as you sift the snow through gloved fingers. Focused so intently on finding the bail, you hardly notice the frigid air pressing against your tired body and sweat-soaked clothes.
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The exertion that warmed you on the way uphill now works against you: Your exercise-dilated capillaries carry the excess heat of your core to your skin, and your wet clothing dispels it rapidly into the night. The lack of insulating fat over your muscles allows the cold to creep that much closer to your warm blood.
Your temperature begins to plummet. Within 17 minutes it reaches the normal 98.6. Then it slips below.
At 97 degrees, hunched over in your slow search, the muscles along your neck and shoulders tighten in what’s known as pre-shivering muscle tone. Sensors have signaled the temperature control center in your hypothalamus, which in turn has ordered the constriction of the entire web of surface capillaries. Your hands and feet begin to ache with cold. Ignoring the pain, you dig carefully through the snow; another ten minutes pass. Without the bail you know you’re in deep trouble.
Finally, nearly 45 minutes later, you find the bail. You even manage to pop it back into its socket and clamp your boot into the binding. But the clammy chill that started around your skin has now wrapped deep into your body’s core.
At 95, you’ve entered the zone of mild hypothermia. You’re now trembling violently as your body attains its maximum shivering response, an involuntary condition in which your muscles contract rapidly to generate additional body heat.
It was a mistake, you realize, to come out on a night this cold. You should turn back. Fishing into the front pocket of your shell parka, you fumble out the map. You consulted it to get here; it should be able to guide you back to the warm car. It doesn’t occur to you in your increasingly clouded and panicky mental state that you could simply follow your tracks down the way you came.
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And after this long stop, the skiing itself has become more difficult. By the time you push off downhill, your muscles have cooled and tightened so dramatically that they no longer contract easily, and once contracted, they won’t relax. You’re locked into an ungainly, spread-armed, weak-kneed snowplow.
Still, you manage to maneuver between stands of fir, swishing down through silvery light and pools of shadow. You’re too cold to think of the beautiful night or of the friends you had meant to see. You think only of the warm Jeep that waits for you somewhere at the bottom of the hill. Its gleaming shell is centered in your mind’s eye as you come over the crest of a small knoll. You hear the sudden whistle of wind in your ears as you gain speed. Then, before your mind can quite process what the sight means, you notice a lump in the snow ahead.
Recognizing, slowly, the danger that you are in, you try to jam your skis to a stop. But in your panic, your balance and judgment are poor. Moments later, your ski tips plow into the buried log and you sail headfirst through the air and bellyflop into the snow.
You lie still. There’s a dead silence in the forest, broken by the pumping of blood in your ears. Your ankle is throbbing with pain and you’ve hit your head. You’ve also lost your hat and a glove. Scratchy snow is packed down your shirt. Meltwater trickles down your neck and spine, joined soon by a thin line of blood from a small cut on your head.
This situation, you realize with an immediate sense of panic, is serious. Scrambling to rise, you collapse in pain, your ankle crumpling beneath you.
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As you sink back into the snow, shaken, your heat begins to drain away at an alarming rate, your head alone accounting for 50 percent of the loss. The pain of the cold soon pierces your ears so sharply that you root about in the snow until you find your hat and mash it back onto your head.
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But even that little activity has been exhausting. You know you should find your glove as well, and yet you’re becoming too weary to feel any urgency. You decide to have a short rest before going on.
An hour passes. at one point, a stray thought says you should start being scared, but fear is a concept that floats somewhere beyond your immediate reach, like that numb hand lying naked in the snow. You’ve slid into the temperature range at which cold renders the enzymes in your brain less efficient. With every one-degree drop in body temperature below 95, your cerebral metabolic rate falls off by 3 to 5 percent. When your core temperature reaches 93, amnesia nibbles at your consciousness. You check your watch: 12:58. Maybe someone will come looking for you soon. Moments later, you check again. You can’t keep the numbers in your head. You’ll remember little of what happens next.
Your head drops back. The snow crunches softly in your ear. In the minus-35-degree air, your core temperature falls about one degree every 30 to 40 minutes, your body heat leaching out into the soft, enveloping snow. Apathy at 91 degrees. Stupor at 90.
You’ve now crossed the boundary into profound hypothermia. By the time your core temperature has fallen to 88 degrees, your body has abandoned the urge to warm itself by shivering. Your blood is thickening like crankcase oil in a cold engine. Your oxygen consumption, a measure of your metabolic rate, has fallen by more than a quarter. Your kidneys, however, work overtime to process the fluid overload that occurred when the blood vessels in your extremities constricted and squeezed fluids toward your center. You feel a powerful urge to urinate, the only thing you feel at all.
By 87 degrees you’ve lost the ability to recognize a familiar face, should one suddenly appear from the woods.
January 27, 2010