Hypothermia, a significant decrease in core body temperature, can appear and escalate quickly in the right conditions. Its physical effects are compounded by hindering the capabilities of severely cold individuals to take the necessary steps to improve their situation. Knowing thermoregulation and how we lose heat to our environment can help anyone venturing into the outdoors make wiser decisions before and after they hit the trail.
We lose body heat to anything we touch that is colder than we are. Glassing for deer while sitting directly on the ground on a chilly morning will draw the warmth right out of you. This is heat loss through conduction, or to something you are directly contacting. It’s the main reason for air or foam mattresses on camping trips. Sure, they provide a softer surface. More importantly, they insulate you from the cold ground. Remember, distance from the cold surface reduces the effects of conduction. Put simply, thicker insulation is warmer.
You can lose valuable body heat to colder objects or frigid air. Heat loss through conduction becomes significantly increased when water is involved. A person in a cool lake or stream will lose warmth at a rate roughly 25 times faster than in air of the same temperature. A hiker or hunter who is both cold and wet is in a potentially life-threatening situation. Get warm and changed into dry clothes to reduce the risk of hypothermia.
Convection in the outdoors is usually experienced as “wind chill.” The air movement that feels like relief on a hot, humid day rapidly strips much needed heat away from you in colder weather. Simply finding a natural windbreak, like a fallen tree or large boulder, can help immensely. The right layers in your pack are also essential. Light windbreakers will work, of course; rain gear will similarly protect you from wind and serves double-duty for wet weather threats.
The wind can also accelerate the loss of body heat through evaporation. This strategy for bodily thermoregulation gives humans a great advantage in being active in hot environments. That’s the whole point of sweating. In cold weather climates, this evaporative cooling is another consideration to be managed. Often outdoor adventurers find themselves perspiring from their exertion or warmer daytime temps. When they slow down to make camp or the sun sets, they find themselves uncomfortably cold- or worse if unprepared. Choose to wear fabrics that dry quickly and carry extra base-layers and socks for camp and sleeping. When this isn’t possible, try to manage your activity level to reduce sweating.
Humans radiate body heat into the environment. You can’t stop this significant loss of heat, but you can contain it. In addition to providing a barrier between you and the colder conditions around you, insulating clothes and gear trap your body heat in their structures. Wool, down, and fleece can all be effective materials for slowing the escape of radiant warmth.
You can also take advantage of sources of radiant heat in the environment. Rest on a dark, sun-warmed boulder on a chilly day. Set up camp on an east-facing slope to catch the first rays of warming sun in the morning. Fill bottles with hot water to radiate inside sleeping bags. Or, practice the most revered of outdoor skills- build a campfire.
Even when hypothermia isn’t a major threat, understanding the principles of thermoregulation can help make your outdoor experiences more comfortable. The confidence gained by employing these strategies will keep you feeling at home in the natural world.
[H/T NOLS, Outdoor Action]