In an ice cap climate, the average temperature of every month stays below 0°C. This is the defining temperature boundary for the Köppen EF classification, where “E” denotes a polar climate and “F” denotes ice cap conditions.
The rule uses mean monthly temperature, not the lowest temperature recorded during a month. A place can therefore have occasional milder days and still qualify, provided its monthly average never reaches or exceeds the freezing threshold. Permanent snow and ice persist because seasonal melting is insufficient to remove the accumulated ice.
Ice cap climate is distinct from tundra climate, coded ET. Tundra has a warmest-month average between 0°C and 10°C, allowing a brief summer thaw and limited vegetation. Ice-cap regions remain too cold for ordinary surface vegetation and are concentrated in Antarctica, Greenland’s interior and some high mountain areas.
The coldest locations on Earth are commonly found in this climate category. Vostok Station in Antarctica, for example, has recorded the planet’s lowest directly measured air temperature and has an exceptionally cold annual average.