As Antarctic sea ice continues its dramatic decline, we need more measurements and much better models to predict its future

This week The Conversation published an article, by Dr Inga Smith with colleagues from Otago and Canterbury universities, which looks at why sea ice loss couldn’t be predicted, changes in sea ice thickness, and the influence of Antarctic storms on local conditions.

After two seasons of record-breaking lows, Antarctica’s sea ice remains in dramatic decline, tracking well below any winter maximum levels observed since satellite monitoring began during the late 1970s.

A layer of frozen seawater that surrounds the Antarctic continent, sea ice cycles from maximum coverage in September to a minimum in February. The summer minimum has also continued to diminish, with three record low summers in the past seven years.

Some scientists have suggested this year could mark a regime shift for Antarctic sea ice. The consequences could be far-reaching for Earth’s climate, because sea ice keeps the planet cooler by reflecting solar energy back into the atmosphere and insulating the ocean. Its formation also generates cold, salty water masses that drive global ocean currents.

The annual freeze-thaw cycle of Antarctic sea ice is one of Earth’s largest seasonal changes, but is a major challenge for climate models to predict accurately.

Since the 1970s, satellites have been tracking a quantity known as “sea ice extent”, which is the total surface area where at least 15% is covered by sea ice.

This September, it reached a satellite-era record low for this time of year. The previous year, after tracking much lower than the median all winter, Antarctic sea ice extent made a late rally and was 18.3 million square kilometres at its maximum by September 2022, around 2% below the 1981-2010 median.

Although 2% might not sound like much, the following summer biologists reported devastating effects on Emperor penguins. No chicks survived in four out of five breeding sites in one region of sea ice loss.

In 2023, Antarctic sea ice extent started the winter even lower than in 2022, and by the end of July was almost 13% below the 1981-2010 median for that time of year. It reached its maximum extent on September 7, at just under 17 million square kilometres, which is nearly 9% below the 1981-2010 median.