How Animals Survive the Coldest Places on Earth

The last glacial period on Earth began to fade around 11,000 years ago where the kilometers-thick ice sheets that covered much of the Earth started to recede and the Earth entered into the Holocene, the current geological epoch.

The once mighty glaciers did not disappear entirely where in the extremes of our Earth, the North and South Poles, are the remnants of the last ice age where these frozen tundras easily reach temperatures as low as negative 40 degrees Celsius and sometimes dip far below that.

Polar regions are places that seem wholly inhospitable to any living creature where temperatures are so low that hypothermia can quickly set in and ice itself can form inside the body, its crystals shredding tissue and ripping cells apart.

Sub-zero temperatures are a problem for all living things because all living things are largely made up of water and when water freezes it expands and becomes sharp where this is frostbite, a death sentence for any cells it forms inside.

Cells that make up vital organs also have optimum operating temperatures and when core body temperature falls the heart, nervous system and other organs cannot work normally where this hypothermic state can lead to complete organ failure and eventually to death.

To survive an extremely cold climate there are two things an animal can do: prevent heat from leaving the body or create more heat through metabolic processes where these fundamental strategies underlie all cold-weather adaptations in the animal kingdom.

The animal kingdom is made up of endotherms and ectotherms, the fancy words for warm-blooded and cold-blooded animals where it is a misconception that cold-blooded animals do not create heat like warm-blooded animals since they do create heat but just cannot retain it and regulate it like the endotherms can.

Endotherms primarily birds and mammals use metabolic heat to maintain a stable internal temperature often one warmer than their environment and when it gets particularly cold outside endotherms can increase metabolic heat production in what is called thermogenesis where one of these methods is shivering.

Some animals especially hibernating ones have an extra heat generating power using a specialized fat tissue called brown fat or brown adipose tissue where animals can create heat without moving a muscle in what is called non-shivering thermogenesis generating 300 times more heat than any other tissue in the body.

Brown fat works very differently from white fat which is the fat we are more familiar with where white fat stores extra energy and is what builds up in obesity but brown fat breaks down sugar and white fat to create heat, burning up calories instead of storing them.

Small mammalian hibernators use brown fat more effectively than any other creature where before hibernation they undergo a large increase in brown fat not to get through hibernation itself but rather to help them get out of it since arousal from hypothermic torpor state is no trivial task taking about one hour and involving violent shaking and muscle contractions while brown fat works to burn off energy stores to rapidly warm the body.

Hibernation involves going into a state of decreased physiological activity usually paired with a reduced body temperature and metabolic rate where this decreased state of activity is called hypothermic torpor which enables animals to survive periods of reduced food availability like in harsh frozen winters.

Creating heat like this comes at a great cost energetically speaking where as much as 75 percent of the total energy expended during a torpor bout is used just for arousal requiring a huge amount of calories to be consumed for any amount of thermogenesis and this is why sometimes it is better to not just create heat but to keep it from escaping in the first place.

The temperature of water in the Arctic Ocean hovers around negative 1.8 degrees Celsius where it can be at a below freezing temperature due to its salt content and since water conducts heat 25 times more effectively than air, water this cold is capable of sapping away large amounts of body heat creating what should be an inhospitable place for mammals.

Marine mammals have an adaptation found nowhere else in the animal kingdom called blubber which is a specialized layer of fat that lives under the skin and is anatomically and biochemically adapted to be an efficient thermal insulator where like other adipose tissue blubber is composed of numerous fat cells called adipocytes which are filled with lipids and blubber can be up to 93 percent lipid with very little water content.

Polar bears have up to 11 centimeters of fat surrounding them to help keep them warm in the water but when on land a different adaptation exists to keep them warm through their heavy fur coat where close to their body is fluffy white fur which traps dry warm air next to the skin and all around that is their outer coat which is made up of hollow transparent hair called guard hairs.

Because of these hollow guard hairs polar bears are almost completely invisible in infrared vision where infrared radiation is a part of the electromagnetic spectrum that we cannot see but can feel as heat since warm bodies emit this radiation which is what infrared cameras can pick up and polar bear guard hairs absorb this radiation more effectively than almost any animal hanging on to the warmth rather than letting it be lost to the cold environment.

The body surface is the main site for heat exchange with the environment especially in those of us with no fur where as warm blood flows to the outside of our body towards the skin heat radiates away and is lost and so when the temperature outside plummets the flow of blood to the skin has to be controlled to keep the body core temperature at a safe level where once the body senses cold it constricts the thin web of capillaries in your extremities starting off with your fingers and toes.

Many endotherms have vasoconstriction ability for when the weather gets cold but to keep their extremities from being damaged some animals have countercurrent heat exchange systems that allow heat to be transferred from blood vessels containing warmer blood to those containing cooler blood where animals like wolves use this extensively in their legs and feet to keep them from freezing as blood leaves the wolf core at a warm body temperature and travels towards the feet while the blood returning from the feet has been cooled down from the environment.

After some time in the cold certain people’s constricted capillaries will suddenly dilate sending a rush of warm blood into the now freezing extremities briefly warming them before constricting again where this prevents the extremities from being severely damaged by frostbite while still ensuring that the vital organs stay warm and the cycle of constriction and dilation is called the hunter’s response where people who live in cold environments or people whose ancestors did have this automatic response and Inuit hunters for example can raise the temperature of the skin in their hands from almost freezing to 10 degrees Celsius in a few minutes.