Each line shows daily sea ice extent—the total area at least 15% ice covered—in the Southern Ocean around Antarctica from 1979 through early 2026. Years 1979–2015 are gray, 2016–2024 (except 2023) are light blue, 2023 is dark blue, 2026 is pink. The 2026 minimum was the first year close to the average extent in several years; 2023 set a record for the smallest summer minimum and winter maximum. The pattern of consecutive years of very low summer extents is unusual, but still not statistically significant because of the wide range of historical variability. Climate.us image, adapted from Charctic data from the National Snow and Ice Data Center.
Climate change: Antarctic sea ice
Monthly average sea ice extent during the winter maximum (top line) and summer minimum (bottom line) around Antarctica from 1979–2026. In most years, the largest monthly ice extent occurs in September and the smallest in February. Climate.us image, based on data from the National Snow and Ice Data Center.
As it does in the Arctic, the surface of the ocean around Antarctica freezes over in the winter and melts back each summer. Antarctic sea ice usually reaches its annual maximum extent in mid- to late September, and reaches its annual minimum in late February or early March.
Antarctic sea ice concentration in September 2026, the month of the maximum winter extent in the Southern Hemisphere. Compared to median conditions from 1981–2010 (yellow line), the most recent minimum was the third lowest on record. Map by Climate.us, based on satellite data provided by the National Snow and Ice Data Center.
Antarctic sea ice reached its 2026 annual minimum on February 26. The summer minimum was 2.58 million square kilometers (996,000 square miles), closer to average than in recent years (which have seen a string of record and near-record lows), but still below the 1981–2010 average. In 2026, Antarctic sea ice reached its annual peak on September 14. The 2026 winter maximum extent was 17.59 million square kilometers (6.79 million square miles). That was the third-smallest winter maximum of the satellite record.
Average Antarctic sea ice concentration in February 2026, the month when sea ice reached its summer minimum extent. The 2026 minimum extent was slightly below average. Map by Climate.us, based on satellite data provided by the National Snow and Ice Data Center.
Scientists have linked large and persistent declines in Arctic sea ice to human-caused global warming, but the picture for changes in Antarctica is less clear. Antarctic sea ice experienced record-low extents throughout much of 2023, and similar low extents, exceeding every previous year in the satellite era except 2023, occurred in 2024. Research studies on the cause of the generally low-ice conditions favor increased upward mixing of warmer ocean water. Whether this is due to natural variability or the start of a climate-change signal is not clear as of October 2026. Making such a determination could require several more years of observations.
Antarctic versus Arctic sea ice
The timing of the seasonal cycles isn’t the only way that Antarctic sea ice differs from the Arctic. Another key difference is the larger range between austral winter maximum extent and summer minimum extent. Historically, Antarctic sea ice has extended to about 19 million square kilometers (7 million square miles) in winter and retreated to about 3 million square kilometers (1 million square miles) in summer. In the Arctic, the range is about 15 million square kilometers (6 million square miles) in winter and 6 million square kilometers (2 million square miles) in summer. In other words, Antarctic sea ice extent is larger than the Arctic's in winter, but smaller in summer.
The differences in seasonal sea ice extremes in the Antarctic compared to the Arctic are largely due to basic geography. The Arctic is an ocean basin centered on the North Pole and largely surrounded by land. Sea ice is always present over the pole area and central Arctic, and it expands southward every autumn. Its expansion is checked by the coasts of Eurasia, North America, and Greenland. The Antarctic is characterized by a continent straddling the South Pole and surrounded by a vast ocean. Sea ice can expand freely across the Southern Ocean in winter, but it can get no closer to the South Pole than the Antarctic coastline will allow, generally between 65 and 75 degrees South. This barrier means that much of the seasonal sea ice around Antarctica forms at lower latitudes (closer to the equator) than the Arctic ice.
Because a substantial amount of Antarctic sea ice forms at warmer latitudes closer to the equator, less ice survives the summer. On average, about 40 percent of the Arctic Ocean’s winter ice cover remains at the summer minimum, whereas in the Southern Ocean only about 15 percent does. Because so little Antarctic ice persists through the summer, the majority of Antarctica’s sea ice is only one winter old. As a result, Antarctic sea ice is relatively thin, often 1 meter (about 3 feet) or less. (In the Arctic, multiyear ice that survives at least one summer is generally 3–4 meters (10–12 feet) thick, and even seasonal ice that formed since the previous summer can often reach about 2 meters (roughly 6 feet) in thickness.)
Young, thin ice floats in the Amundsen Sea on October 16, 2009. The brighter the ice, the more it has been compacted by wind and waves. Photo captured by the DMS camera on the first flight of NASA’s Operation IceBridge Campaign. Photo courtesy NASA Earth Observatory.
So overall, average Antarctic ice thickness is much lower than Arctic sea ice. However, snowfall often thickens Antarctic sea ice. The heavy snow burden can depress ice floes, and seawater can subsequently flood the snow layer. This saturated snow can freeze, forming “snow ice,” an important component of southern sea ice. Although this can occur in the Arctic as well, it is less common.
Variability and long-term change
Sea ice waxes and wanes with the seasons, and minimum and maximum summer and winter extents vary. Compared to the Arctic, Antarctic sea ice shows lower variability in summer, and higher variability in winter. These changes largely result from the geographic differences mentioned above, namely Antarctic sea ice’s distance from the pole (sea ice can melt back only as far as the coast in summer) and unconstrained growth potential in winter. Weather events often drive variability, but have different effects in the Northern and Southern Hemispheres. Weather exerts a greater influence on the Arctic minimum, and the Antarctic maximum.
The modern sea ice satellite record dates back to October 25, 1978. (Full-month sea ice statistics are available since November 1978, and full-year statistics are available since 1979.) Unlike the Arctic, where sea ice extent is declining in all areas in all seasons, Antarctic trends are less apparent. Over 1979–2015, Antarctic-wide sea ice extent showed a positive trend overall, although some regions experienced declines. Those exceptions have primarily occurred around the Antarctic Peninsula. Another region near the northern tip of the Peninsula, in the Weddell Sea, showed strong sea ice declines until 2006, but the ice in that region rebounded in the 2010s; most recently it has declined slightly again. The eastern Ross Sea region has shown a modest increase in ice extent over the same period.
Overall, the long-term trend in Antarctic sea ice, spanning nearly 50 years, is statistically flat (in contrast, the glaciers and ice sheets over land in Antarctica have lost mass through this period.) The satellite record spans more than four decades, and although the ice has shown increasing and decreasing trends over portions of that record, few of those trends have been statistically significant. Year-to-year variability has dominated. Since the year 2013, the highest-ever winter maximum occurred in September 2014, and the lowest-ever summer minimum was in February 2023. But the overall trend, as of late 2026, is close to zero.
According to the National Snow and Ice Data Center’s Sea Ice Index, from the start of the satellite record in November 1978 through September 2026, trends for all months have been negative, thanks largely to recent low extents. But in only one month—November—is the declining trend significant, and only just.
A study published in 2022 reconstructed Antarctic sea ice back to 1905 using a combination of several climate models. The study found that, prior to the continuous satellite record, Antarctic sea ice experienced declining trends over much of the early and mid-twentieth century.
Impacts of change
Land-sea configurations affect sea ice extents not only by limiting where ice can form, but also by introducing their own effects. In the Arctic, landmasses surround and influence the sea ice in the Arctic Ocean. Ice and (especially) snow are highly reflective, bouncing much of the Sun’s energy back into space. As Northern Hemisphere spring and summer snow cover declines, the underlying land surface absorbs more energy and warms. Warmer conditions on land affect the nearby ocean, and more sea ice melts as a result. As sea ice melts, more of the ocean warms. The melt-warmth-melt feedback cycle means that the Arctic is warming faster than the rest of the globe. At present, Arctic sea ice loss is a leading contributor to Arctic amplification.
No such polar amplification effect has occurred on a large scale in the Southern Hemisphere, however. Antarctica is surrounded by ocean, not a land surface that is losing its reflective snow and ice cover in the spring and summer. It was already normal, historically, for summertime sea ice to melt back nearly to the Antarctic coastline, leaving large expanses of the Southern Ocean exposed to heating from the summer sun. By contrast, the loss of reflective snow and ice in high northern latitudes surrounding the Arctic Basin represents a profound change from what was historically normal.
Satellite images of sea ice off the Oates Coast of Antarctica on October 7, 2018, (left) and January 12, 2019 (right). Unlike the Arctic, the Antarctic typically holds on to very little sea ice in the summer. Suomi NPP satellite images from Worldview.
The Southern Ocean is vast, a fact often underplayed in map projections focused on the Northern Hemisphere. Natural cycles in the Southern Ocean can have pronounced effects on Antarctic sea ice. Atmospheric patterns, partly influenced by greenhouse gas emissions, are also at work.
The Southern Annular Mode (SAM) is a pattern of westerly winds circling Antarctica. The SAM is influenced by El Niño-Southern Oscillation (ENSO) conditions, so it is partly driven by natural oscillations. At the same time, research has found that human-caused global warming tips the SAM into its positive mode more frequently, and the resulting wind effects generally tend to increase Antarctic sea ice extent. The SAM also affects the Amundsen Sea Low, which in turn affects sea ice transport and weather conditions over a broad area from the western Antarctic Peninsula to the eastern Ross Sea.
Several consecutive years of below-average Antarctic sea ice extent, however, have captured growing attention from researchers. At the time of the record-low extent observed in February 2023, Ted Scambos, senior research scientist at the University of Colorado, Boulder, said, “If lower-than-average Antarctic sea ice extent continues, despite a shift in ENSO or with a range of SAM index values, it would be a strong indication that we’re seeing a climate or ocean warming signal emerging from the high variability of the Antarctic system.” The February 2026 minimum was much closer to the long-term average, but this was due largely to wind-driven northward movement of sea ice in the Weddell Sea, according to the National Snow and Ice Data Center analysis.
Long story short: Climate change has a discernible influence on Arctic sea ice, but it has a complicated, messy influence on Antarctic sea ice. (Meanwhile, the Antarctic Ice Sheet is still losing mass overall, despite recent snowfall gains in East Antarctica.)
Where sea ice does melt away completely in the Antarctic summer, the ice’s absence can have cascading effects. For example, sea ice retreat in the Weddell Sea along the northern tip of the Antarctic Peninsula probably contributed to Larsen Ice Shelf losses. Ice shelves—thick slabs of floating ice attached to coastlines and usually fed by glaciers—fringe the frozen continent. Intact sea ice in front of an ice shelf buffers the shelf from ocean swells. When the ice is gone, ocean waves can flex the shelf and make it more vulnerable to disintegration. Depending on how much an ice shelf disintegrates, the glacier feeding it may accelerate into the ocean.
If the current reduced ice extents persist, they too can have a cascading effect. With longer periods of time without ice cover, especially at the northern fringe of the Antarctic sea ice pack, solar heating can warm the upper ocean. This added heat may delay re-freezing of the ocean in the following winter, extending a trend that may be initiated by increased upward mixing of warmer, deeper ocean layers.
Another potential impact of reduced sea ice cover is greater accumulation on the continent, as winds from the open ocean reach the ice sheet without first flowing over an extensive sea ice fringe. This tends to reduce the impact of sea level rise from the ice sheet.
References
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