Antarctic Ice Sheet

The Antarctic ice sheet is one of the two polar ice caps of the Earth.

It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth. It covers an area of almost 14 million square kilometres (5.4 million square miles) and contains 26.5 million cubic kilometres (6,400,000 cubic miles) of ice. That is, approximately 61 percent of all fresh water on the Earth is held in the Antarctic ice sheet, an amount equivalent to about 58 m of sea-level rise. In East Antarctica, the ice sheet rests on a major land mass, but in West Antarctica the bed can extend to more than 2,500 m below sea level. Much of the land in this area would be seabed if the ice sheet were not there.

In contrast to the melting of the Arctic sea ice, sea ice around Antarctica was expanding as of 2013^[update]. The reasons for this are not fully understood, but suggestions include the climatic effects on ocean and atmospheric circulation of the ozone hole, and/or cooler ocean surface temperatures as the warming deep waters melt the ice shelves.

The icing of Antarctica began with ice-rafting from middle Eocene times about 45.5 million years ago and escalated inland widely during the Eocene–Oligocene extinction event about 34 million years ago. CO₂ levels were then about 760 ppm and had been decreasing from earlier levels in the thousands of ppm. Carbon dioxide decrease, with a tipping point of 600 ppm, was the primary agent forcing Antarctic glaciation. The glaciation was favored by an interval when the Earth's orbit favored cool summers but oxygen isotope ratio cycle marker changes were too large to be explained by Antarctic ice-sheet growth alone indicating an ice age of some size. The opening of the Drake Passage may have played a role as well though models of the changes suggest declining CO₂ levels to have been more important.

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