As in other extreme climates, only specially adapted plants and animals can live in the coldest parts of the world. In fact, at the North and South Poles, almost nothing can survive, but around the edges of the Arctic and Antarctic there are seas rich in plant and animal life. This means that larger animals, living on the edge of the ice, can find food in the teeming waters.
Air temperatures averaging below freezing over the year (usually well below freezing) with a range in many places around -40°C to +10°C (-40°F to +50°F) and highs (very briefly and rarely) up to +22°C (+72°F) amongst rocks and moss banks. Much of Antarctica is a cold largely featureless icy desert where above freezing temperatures are hardly reached if ever at all. The temperature of the Antarctic Ocean that surrounds the continent varies from -2°C to +2°C (+28.4°F to +35.6°F) over the year. Seawater freezes at -2°C (+28.4°F) so it can’t get any colder and still be water.
Arctic and Antarctic birds and mammals such as penguins, whales, bears, foxes and seals – are warm blooded animals and they maintain similar internal body temperatures to warm blooded animals in any other climate zone – that is 35-42°C (95-107°F) depending on the species. They have to keep high body temperatures to remain active. These animals are known as endotherms (endo-inside + therm-heat) as they generate their heat internally. The Polar Regions’ cold and wind mean that this heat can very quickly be lost leading to hypothermia (hypo-under).
Many (non-polar) animals are ectotherms (ecto-outside) , which means that they generate so little heat internally they are dependent on the external environment to warm them up to a level where their body and enzymes function sufficiently well enough for an active and functional life. Typically they raise their temperature by basking in the sun until they are warm enough to become active. Reptiles and amphibians do this while invertebrates are usually small enough to be able to warm up quickly to the ambient temperature from the air alone without basking in direct sunlight.
A large ectothermic Arctic or Antarctic land animal would never get enough energy regularly enough from the surroundings to become sufficiently active once it had cooled. All polar land animals of any size therefore need to be warm-blooded to be active. The environment is so extreme that the size limit in Antarctica for an ectotherm is about 13mm, the size of the largest fully terrestrial (land) animal in Antarctica. In other words any animal larger than this would be unlikely to be able to warm up enough to become active before it started to get cold again.
