Maxed out: How cold can you get and live?
By James Mitchell Crow Humans hate being cold, and for good reason: our long-limbed bodies are exquisitely adapted to lose heat, not to retain it. This makes perfect sense in the intense heat of the African savannah, where humans evolved. Without our technological adaptations to cold – clothing, heating, shelter – that’s where we’d all still be living, says Mike Tipton of the University of Portsmouth, UK, who studies human thermoregulation. Surviving the cold is all about protecting core body temperature. This is usually at 37 °C, but it takes surprisingly little for it to start dropping. An ambient temperature of 20 °C can induce hypothermia if conditions are wet and windy, says François Haman, a physiologist at the University of Ottawa, Canada. When cold, the body starts to shiver and shuts down blood flow to the extremities. If core temperature falls by just 2 °C, hypothermia sets in: first we start to lose consciousness, then the heart loses rhythm. Death follows at about 24 °C, when the heart stops. Usually. People have been known to survive much lower core body temperatures. Anna Bagenholm survived the biggest drop ever recorded, to 13.7 °C, when she fell into a part-frozen stream and became trapped under ice for 80 minutes. The constant flow of icy water cooled her body to such an extent that by the time her breathing and heart had stopped, her brain needed very little oxygen in order to survive, giving her the chance of complete recovery. Read more: Maxed out: