Antarctic Sea Ice: Why It Grew Until 2014 and Why It Is Now Shrinking

For more than three decades, the sea ice around Antarctica did something that puzzled scientists: while Arctic ice shrank dramatically, Antarctic sea ice grew slightly. In 2012 and 2013, two studies explained part of the mystery with winds and meltwater. Then, after 2016, the trend reversed sharply, and in 2023 the ice fell to record lows. Here is what changed and what the science says.

Antarctic sea ice: the seasonal cycle

Sea ice is frozen ocean water, quite different from the glaciers and ice sheet that cover the continent itself. Because it already floats, its melting does not raise sea level; land ice does. Antarctic sea ice has one of the biggest seasonal swings on Earth. It shrinks to about 3 million square kilometres at its February minimum and spreads to about 18 million square kilometres by September, at the end of the southern winter.

Compared with Arctic ice, Antarctic sea ice is on average younger, thinner, warmer, saltier and more mobile. Most of it is first-year ice less than a few metres thick, and because it is covered by snow it melts mainly from below. The Arctic Ocean is almost enclosed by land, while Antarctic ice can spread freely into the open Southern Ocean.

Why Antarctic sea ice grew until 2014

Satellites have tracked sea ice since late 1978. The IPCC’s Fifth Assessment Report found a likely increase in Antarctic extent of 1.2 to 1.8 percent per decade between 1979 and 2012, and from 2007 to 2016 extent was mostly above average. Two studies offered explanations.

• Winds. In November 2012, Paul Holland of the British Antarctic Survey and Ron Kwok of NASA’s Jet Propulsion Laboratory published in Nature Geoscience the first direct satellite evidence of long-term changes in Antarctic ice drift, built from more than five million daily ice-motion measurements over 19 years. Shifting winds pushed ice away from the coast in some regions and reduced it in others; the regional gains and losses nearly cancelled out, leaving a small overall increase.
• Meltwater. In March 2013, Richard Bintanja and colleagues at the Royal Netherlands Meteorological Institute (KNMI) argued in the same journal that faster melting of the floating ice shelves was a major factor. The cold, fresh meltwater forms a surface layer that shields the surface from warmer deep water, helping sea ice expand in autumn and winter despite a warming atmosphere.

The IPCC’s later Sixth Assessment Report also points to changes in the westerly winds of the Southern Hemisphere, linked to natural variability, greenhouse gases and the ozone hole.

The reversal: record lows since 2016

After 2014 the ice began to decline, and since 2016 extent has mostly been below average. The decline coincides with rising heat content in the upper ocean, which points to a strong oceanic influence. The records followed quickly:

• February 2022: a record low summer extent of about 1.9 million square kilometres.
• 21 February 2023: a new record minimum of 1.79 million square kilometres, according to the U.S. National Snow and Ice Data Center (NSIDC).
• September 2023: a record low winter maximum of 16.96 million square kilometres, nearly one million square kilometres below the previous lowest maximum, from 1986.
• 1 March 2025: a minimum of 1.98 million square kilometres, tied with 2022 and 2024 for second lowest in the 47-year satellite record.

For comparison, the 1981 to 2010 average minimum is 2.84 million square kilometres.

What the Antarctic sea-ice record tells us

Over the whole satellite era, the Antarctic trend is still close to flat: NSIDC calculates a decline of about 2.3 percent per decade relative to the 1981 to 2010 average, a trend that is not statistically significant. The IPCC found no significant trend from 1979 to 2020 in either summer or winter. The short-term swings, however, have become very large.

The wind and meltwater studies of 2012 and 2013 remain important, because they showed how Antarctic ice responds to forces that barely exist in the Arctic. The post-2016 lows, linked to a warmer upper ocean, show that the balance can shift quickly, which is why each new NSIDC summer minimum is now closely watched.

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