Antarctic sea ice reached its third-lowest winter maximum in satellite records; the latest measurement adds another data point to scientists’ assessment of long-term changes in polar ice

According to NASA and the National Snow and Ice Data Centre (NSIDC), Antarctic sea ice likely reached its annual maximum extent for the year on September 14. On the date, the ice covered an estimated 17.59 million square kilometres, making it the third-lowest maximum on record. It has fallen a million square kilometres or almost 400,000 square miles short of the long-term average, as per scientists.Confirmation of the peak meant the four lowest years on record for the continent’s sea ice, a vital component of the planet’s climate and critical for marine life, had all occurred in the past four years. Dr Walt Meier, a senior scientist at the National Snow and Ice Data Centre at the University of Colorado, said the centre had held off in declaring the maximum because there was a “lot of potential variability” at this stage in the continent’s sea ice cycle.Antarctic ice usually peaks in September, around the end of the Southern Hemisphere’s winter and retreats to a minimum in February. Unlike the Arctic, an ocean basin surrounded by land, the Antarctic is a large continent surrounded by an ocean and this provides the sea ice with more room to expand during winter. But this also lets the ice stretch to warmer latitudes, leading to more melting during summer.But recent years have seen records broken for low sea ice in both winter and summer, raising concerns that global heating could be driving the losses. “The past four winters have had the lowest sea ice maximum on record – that’s a very clear indication of a system that has changed,” said Dr Ariaan Purich, a Southern Ocean expert at Monash University in Melbourne.“This is not a one-off event any more. The sea ice is no longer covering the same extent of ocean that it used to. We are seeing low winter after low winter and that suggests the sea ice is behaving differently because we have warmed our climate. “This is not a future problem. It’s a now problem.”From 1979 to 2014, the total Antarctic sea ice increased by about 1 per cent per decade. For three consecutive years, from 2012 to 2014, satellites observed new record highs for winter sea ice extent. However, this climb came to an end in 2015, and since 2016, significant decreases in sea ice around Antarctica began to occur in 2016. There have since been years with small rebounds, but overall, Antarctic sea ice coverage has largely remained lower than normal. Both the record low minimum and record low maximum occurred in 2023. Scientists will continue to observe the area each year to find out if the decline is part of a long-term change or a statistical fluctuation.To determine sea ice extent, scientists rely on satellites with passive microwave sensors that measure the microwave energy Earth naturally emits. Sea ice emits more of this energy than open water, so it stands out in microwave images. Because microwaves pass through clouds, the satellites can observe sea ice regularly, regardless of weather.The record began in late 1978 with data collected by NASA’s Nimbus-7, followed by Defence Meteorological Satellite Program (DMSP) satellites starting in 1987, and by NASA’s Aqua satellite between 2002 and 2011. In 2025, scientists began using observations from the Japan Aerospace Exploration Agency’s GCOM-W satellite.