Has the world’s sea ice reached a tipping point?

Antarctic Sea Ice (British Antarctic Survey)

There is no shortage of people telling us that we have reached an important inflection point regarding the world’s polar sea-ice sheets. The BBC tells us that the World’s sea-ice has fallen to a record low, informing us that the Arctic end-of-summer extent fell from an average of 7 million sq km in the 1980s to 4.5 million sq km in the 2010s.

It adds that, on the other side of the world, until the mid-2010s, Antarctic sea-ice had been remarkably resilient, defying predictions that it would shrink. Since then, however, the continent has shown a series of very low sea-ice extents, although there is still lots of natural variability.

You can interrogate the data yourself and see just how variable it is.

Daily lows

This year, Arctic daily sea-ice extent has been hovering near record daily lows, with the ice edge well north of its long-term average position in most areas. The extent for January 2025 averaged 13.13 million square kilometers (5.07 million square miles), the second lowest value for the month in the satellite record, following a record lowest extent for December 2024.

In the Antarctic, daily sea-ice extent fell below the long-term average after a brief period of above-average daily extents, ending January just below the lowest 10 percent of ice extents for the day. The January extent was 50,000 square kilometers (19,000 square miles) above the record low for the month set in 2018 (Figures 1a and 1b), and 1.29 million square kilometers (498,000 square miles) below the 1981 to 2010 average.

The Antarctic data comes after two remarkable years. 2023 was exceptional in the satellite record for its sea ice, remaining below the climatological fifth percentile for almost the entire year. There was a slight recovery in 2024.

Gilbert and Holmes say that, while this could be part of a decline in sea ice associated with human-caused climate change, it is too early to say conclusively if this is the case.

How rare?

The British Antarctic Survey however, is sure that the record low Antarctic sea ice ‘extremely unlikely’ without climate change.

They calculate it’s a less than one-in-a-2000-year event without climate change, and that it would be four times more likely with human-induced climate change!

Personally, I worry about climate attribution studies that conclude a particular event is likely to occur by chance less than once in over two thousand years. Given the uncertainties in the models and their spread I have no great confidence in the robustness of such figures.

It will be interesting to see what happens, as presumably a recovery could not be explained by the same models. Interestingly there was more Antarctic sea ice in January 2025 than in January 1980.

Resilient Antarctica

A new study suggests that a major Antarctic ice-shelf is far more resilient than had been thought, withstanding an intensive period of hot temperatures some 120,000 years ago.

There has been much debate about the stability of the West Antarctic Ice Sheet (WAIS). University of Cambridge researchers looked the behaviour of the Ronne ice shelf – the second largest bounding the WAIS – during the last interglacial period, between 117,000 and 126,000 years ago. They examined salt concentration in ice cores, which provides an indication of its extent in that period.

Finding that it is more stable and larger than models predict for the conditions of the time suggests a lower likelihood of the collapse of the West Antarctic sheet in response to global warming.