Cold environments

Cold environments are found at high latitudes, where the sun is low in the sky and gives little heat:

• Polar areas are mostly covered in ice: Antarctica and the Greenland ice sheet. The lowest temperature ever measured, −89.2 °C, was at Vostok Station in Antarctica in 1983. Very little snow falls, so the interior of Antarctica is a desert.
• Tundra is the treeless land around the Arctic Ocean: northern Alaska, Canada, Scandinavia and Russia. Winters are long, dark and very cold; summers are short and cool, with long days.

A tundra climate (data written for this app).

• Very cold winters: averages of about −25 °C or lower for several months.
• Short, cool summers: only four months average above freezing, and the warmest averages about 7 °C.
• Dry: about 110 mm of precipitation a year, mostly as summer rain. Winter snow is light, but cold winds blow it around.

The short summer is the only time plants can grow.

Below the tundra lies permafrost: ground that stays frozen for at least two years in a row, often for thousands of years.

• In summer, only the top layer thaws: the active layer, from a few centimetres to about a metre deep.
• Meltwater can't drain through the frozen ground below, so the surface becomes waterlogged, with bogs and shallow lakes.
• In the cold, dead plants decay very slowly, so the soils are thin, acidic and low in nutrients, often with a layer of peat on top.

Permafrost stores huge amounts of carbon in this frozen dead matter.

The parts of the tundra are interdependent: plants insulate the permafrost and feed animals; animals spread seeds and add nutrients; Indigenous peoples herd or hunt caribou and reindeer. If plants are damaged, the permafrost beneath thaws, and the ground sinks and floods.

Plant adaptations:

• They grow low and close together, out of the wind and under snow, which insulates them: the Arctic willow grows only a few centimetres tall.
• Shallow roots fit the thin active layer.
• Small leaves lose little water. The bearberry keeps its leaves all year, ready to grow as soon as summer comes.
• Mosses and lichens survive drying out and freezing.

• Polar bears have thick fur and a layer of fat, and large feet to spread their weight on snow and ice.
• Arctic foxes grow a white coat in winter for camouflage, and have small ears to keep heat in.
• Caribou have wide hooves and migrate south in winter.
• Emperor penguins huddle together in the Antarctic winter to share warmth.
• Many birds, such as the snow goose, come only for the summer to breed.

Biodiversity is low, because few species can survive the cold. Climate change, oil and gas development, and overfishing in the seas around them all threaten it.