Antarctic sea ice extent

Antarctic sea ice extent measures the total area of the Southern Ocean covered by at least fifteen percent sea ice, counted in millions of square kilometres. It comes from satellite microwave sensors that detect the sharp contrast between open water and ice regardless of darkness or cloud, which the National Snow and Ice Data Center compiles into a daily index reaching back to 1979. The swing through the year is enormous: the floating ice ring shrinks to roughly three million square kilometres in late February, then expands to around eighteen million by September, one of the largest seasonal changes on Earth's surface. It matters because sea ice reflects sunlight, insulates the ocean, and drives the dense water sinking that helps power global circulation. One caveat: extent counts any partly covered area in full, so it says little about ice thickness or total volume.

Record high

20.201 million km², 20 Sep 2014

Record low

1.848 million km², 21 Feb 2023

First measurement

26 Oct 1978

Measurement cadence

daily

Measurements in this record

15,864