Polar climate (ET tundra, EF ice cap in Köppen) is characterised by extreme, permanent cold. In tundra (ET), the warmest month reaches 0–10 °C and permafrost covers the ground. In ice cap climate (EF), no month exceeds 0 °C (interior Antarctica, Greenland).
Vostok station (Antarctica) recorded −89.2 °C, the lowest temperature ever measured. The polar vortex keeps cold air confined, but its disruptions send cold waves toward mid-latitudes. Arctic warming is transforming the tundra, releasing carbon from permafrost.