Antarctic sea ice peaked on Sept. 14 at its third-lowest maximum on record

Antarctic sea ice reached its yearly maximum on Sept. 14, 2026, covering about 17.59 million square kilometers, or 6.79 million square miles. That makes it the third-lowest maximum since satellite observations began, according to NASA’s Earth Observatory, which published its analysis on Oct. 12 using data from the National Snow and Ice Data Center.

The ranking leaves 2026 close to the bottom of a record that now includes two years of striking weakness. For most of the winter growth season the frozen ring around the continent tracked near record lows, and the peak, when it arrived, fell well short of what scientists considered normal for the period before 2016.

The 17.59 million square kilometer peak

NASA’s page, written by Michala Garrison, defines sea ice extent as the area where at least 15 percent of the ocean surface is covered by ice, a threshold scientists commonly use. The Earth Observatory analysis notes that Antarctic sea ice usually peaks in September and then retreats to a minimum in February, so a Sept. 14 maximum fits the normal calendar even though the size does not. Both the record low minimum and the record low maximum occurred in 2023, a mark that 2026 did not break but approached.

The center that supplies the data had flagged the likely peak earlier. In its Sept. 23 news story, the National Snow and Ice Data Center said extent most likely peaked on Sept. 14 at 17.59 million square kilometers and would stand as the third-lowest maximum on record if that date held. Senior scientist Ted Scambos said Antarctica’s sea ice during this year’s growth season had steadily lagged the long-term average.

Why a maximum can take weeks to confirm

Calling a maximum is harder than it sounds. NSIDC noted that the peak typically arrives in late September or early October but has come as early as Aug. 30, and large fluctuations near the top of the curve can delay confirmation, because a late storm or a shift in wind can push the edge outward again after a preliminary high. That is why the Sept. 23 story hedged with the phrase “most likely,” and why NASA’s Oct. 12 page could present the figure as settled.

The measurement itself comes from passive microwave sensors, which detect sea ice because it emits more microwave energy than open water. Microwaves pass through clouds, so observations are not blocked by weather or by the long polar night, which is why the record can be compared year-round; NASA’s Earthdata sea ice pages catalog the underlying data. The record began in late 1978 with NASA’s Nimbus-7, continued with Defense Meteorological Satellite Program spacecraft from 1987, drew on NASA’s Aqua from 2002 to 2011, and since 2025 has also used Japan’s GCOM-W satellite.

The season followed an unusual arc. NSIDC’s March 9 analysis, which NASA cites, described the Antarctic minimum as near average, yet the freeze-up that followed did not keep pace. By the time of the Sept. 23 story, extent had tracked near record lows for most of the growth season, and the final peak landed in third place from the bottom. Scientists compare each year with the 1981 to 2010 average, drawn on the NASA chart as a dashed blue line, and 2023 appears in orange as the extreme case.

From the 2012 to 2014 highs to the post-2016 decline

The southern pattern has no tidy story. From 1979 to 2014, total Antarctic sea ice grew by about 1 percent per decade, though NASA says it is uncertain whether that was meaningful change, because extent varies a lot from year to year. Satellites recorded new winter highs for three consecutive years from 2012 to 2014, while Arctic ice was declining steeply.

The climb ended in 2015, and significant decreases began in 2016. NASA says some years have brief rebounds but that overall, Antarctic sea ice coverage has largely remained lower than normal. Scientists will keep monitoring to determine whether the drop is a long-term change or a statistical fluctuation, an honest statement of uncertainty from an agency that has watched the same ocean for more than four decades.

The north offers a contrast. NSIDC reported that Arctic extent likely reached its 2026 minimum on Sept. 12 at 4.60 million square kilometers, tenth lowest in the satellite record and tied with 2008, 2010 and 2025. NASA published a companion item, Arctic Sea Ice Shrinks to Its 2026 Minimum, covering that side of the planet. Mark Serreze, NSIDC’s director, said the Arctic ice was only tenth lowest in extent but that there was loose ice all the way to the pole.

The southern numbers say something modest and specific: one September, one peak, one rank. Whether 2026 belongs to a lasting regime of lower Antarctic ice or a long swing that will turn again is the question NASA leaves open, and the February minimum, tracked on NASA’s Antarctic sea ice record, will be the next data point.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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