- The Arctic: Lowest February sea-ice extent since the beginning of satellite observations
- New study: Even limited global warming will fundamentally transform the ice landscapes of the Arctic
- The Antarctic: There is every indication that the summer sea-ice melting is now over
Sea-ice development in the Arctic: Far below the trend
In February 2025, the mean monthly sea-ice extent in the Arctic Ocean was lower than in any February since the beginning of satellite observations. If we look at the annual cycles of the sea-ice extent, we see that the curve for 2025 was only higher than the curve for winter 2017/2018, one in which there was also very little sea ice, for a few days at mid-month. For the remainder of the month, it was far below the curve and even farther below the long-term mean for the period 1981 – 2010. At certain points, satellites detected up to 540,000 square kilometres less sea-ice cover than in winter 2017/2018. In terms of the monthly mean sea-ice extent, February 2025, at 13.72 million square kilometres, represents a new record low.
Figure 1: Development of sea-ice extent in comparison: Except for a few days at mid-month, the sea-ice extent in February 2025 was far below the curve for winter 2017/2018.
Figure 2: Development of mean sea-ice extent in the Arctic for the month of February. The light blue line underscores the long-term decline in sea ice. After six years above the trend line, the monthly mean value fell below the line in February 2025. There were already indications of this development in January.
The decline in sea-ice extent from the end of January to the second week of February is readily apparent. Normally, at this point in the Arctic winter, new ice should be forming in many regions. Instead, winds most likely drove together the remaining sea-ice cover, while given the unusually high temperatures, it can be assumed that little or no new ice formed in the ice-free regions. “Our maps of the mean temperature deviations show that in many areas, the air masses over the Arctic Ocean were up to 6 degrees Celsius above the mean value for the reference period in February. This warming situation emerged in late January and continued for several weeks. Given these conditions, it’s hardly surprising that, in many regions of the Arctic Ocean, less new sea ice formed,” says Dr Renate Treffeisen, an atmospheric researcher and co-founder of the Sea Ice Portal (Figure 3). The maximum of the heat signal lies between the north of Greenland and the central Arctic and reaches more than 12 degrees Celsius compared to the long-term average in the reference period 1971 - 2010.
In some of the particularly warm regions, the satellites also recorded substantially less sea ice compared to the long-term mean in February. This was the case in e.g. the Bering Sea, but also in the northern Baltic (Gulf of Bothnia), in the southeast Barents Sea to south of the Kola Peninsula, and in the Sea of Okhotsk (Figures 4 & 5).
Figure 3: Air temperature anomalies in February 2025 compared to the long-term February mean for 1971 – 2000. Based on daily mean temperatures measured at an altitude of ca. 760 metres.
Figure 4: Map of the mean sea-ice concentration in the Arctic in February 2025. Small areas of ice in the northern Baltic, southeast Barents Sea and Sea of Okhotsk are clearly recognisable. The bright green line marks the mean February sea-ice extent for the years 1981 – 2010.
Figure 5: Difference in the mean position of the ice margin in February 2025, compared to the long-term mean for the years 2003 – 2014. Regions marked in blue had more Arctic sea ice than the reference period; those marked in red had less.
How the Arctic sea ice will develop in the last weeks of winter 2024/2025 remains to be seen. “In our experience, the sea-ice extent in the Arctic can increase up to mid-March. Whether that will also happen this winter, or whether the maximum winter sea-ice extent was already reached back in February, is something the coming weeks will show,” explains Dr Klaus Grosfeld, an AWI expert and co-founder of the Sea Ice Portal.
Forecast for tomorrow’s Arctic: Disappearing ice landscapes
In February, an international team of sea-ice experts published a new study on the future climate of the Arctic. In it, they summarise the current state of knowledge concerning the impacts of climate change in the Arctic and describe in particular how the Arctic sea ice, Greenland Ice Sheet and Arctic permafrost soils will change if all countries meet their agreed-upon climate targets, limiting global warming to roughly 2.7 degrees Celsius by 2100.
According to the study, this level of warming would fundamentally reshape the Arctic. For example, on virtually any given day of the year, the air temperature would be above the highest levels from the preindustrial era. The Arctic Ocean would be ice-free for several months in summer. On the Greenland Ice Sheet, the area in which the surface temperature was above 0 degrees Celsius for more than a month at a time would quadruple in comparison to the preindustrial era. As a result, the ice sheet would lose more mass, accelerating global sea-level rise. The total area of permafrost and permanently frozen soils in the Arctic would be cut in half. “Our findings clearly show that human beings already have the power to wipe entire landscapes from the surface of the planet,” concludes Hamburg-based sea-ice researcher Prof Dirk Notz. He is part of the Sea Ice Portal’s team of experts and was a co-author of the study. (You can find more detailed information on the new study here.)
Southern Ocean: The summer melting is almost certainly over
In the Antarctic, the summer sea-ice melting accelerated in the first half of February (Figure 6). The sea-ice decline was so rapid that, for ten consecutive days, the annual cycle curve was below the span of the minima and maxima for the reference period 1981 – 2010. Most likely, the sea-ice extent in the Southern Hemisphere has already reached its summer minimum. If the trend from the last week of February continues and the sea-ice extent grows further in March, 22 February 2025 will mark the date of the summer sea-ice minimum. On that day, the residual area of Antarctic sea ice measured 2.16 million square kilometres. The monthly mean sea-ice extent was 2.45 million square kilometres – the fourth-lowest monthly mean value for February in the Antarctic ever recorded by satellite (Figure 7).
Figure 6: For nearly half of February, the daily sea-ice extent curve for the Antarctic was below the Sigma span (turquoise band). The summer sea-ice minimum was most likely reached on 22 February 2025.
Figure 7: Development of mean sea-ice extent in the Antarctic for the month of February. The light blue line underscores the long-term decline in sea ice. In February 2025, the sea-ice extent was far below the trend line for a fourth consecutive year, continuing the slightly negative trend since 2016.
In comparison to the sea-ice concentration in the years 2003 – 2014, in February a great deal of pack ice was missing, above all in the eastern Weddell Sea, off the coast of West Antarctica, and in the Ross Sea (Figure 8). In all three regions, the extensive ice-free areas were most likely attributable to winds. In the Weddell Sea, for example, winds pushed the ice drift westward; in the Ross Sea, air currents drove the pack ice out to the open ocean. In contrast, there were more floes in smaller coastal regions of East Antarctica and off the coast of Marie Byrd Land, where a large accumulation of pack ice survived the summer (Figures 9 and 10).
Figure 8: Difference in the mean position of the ice margin in February 2025, compared to the long-term mean for the years 2003 – 2014. Regions marked in blue had more Antarctic sea ice than the reference period; those marked in red had less.
Figure 9: Mean monthly value for the sea-ice concentration in the Antarctic for February 2025. The lack of pack ice in the Bellingshausen Sea and Amundsen Sea (West Antarctica) is clearly recognisable. In contrast, the accumulation of pack ice off the coast of Marie Byrd Land appears cloudlike. The bright green line marks the mean February sea-ice extent for the years 1981 – 2010.
Figure 10: Mean pressure anomalies at sea level in the Antarctic in February 2025, in comparison to the reference period 1971 – 2000. Arrows represent the wind vectors.
Sea-ice experts from the Alfred Wegener Institute had the chance to observe the loss of sea ice in the eastern Weddell Sea first-hand, as part of an expedition to the area on the research icebreaker Polarstern: “Due to the ice-free waters in the eastern Weddell Sea, all of the oceanographers’ planned work with moorings went very smoothly. But we sea-ice researchers weren’t so lucky: we couldn’t go on any sea-ice thickness survey flights by helicopter because either the weather conditions were too poor, or because the distance between the ship and dense pack ice was much too great for a flight to be worthwhile,” reports AWI sea-ice physicist Prof Stefanie Arndt from on board the Polarstern.
Given the ice-free conditions in the eastern Weddell Sea, the cruise leader opted to take the ship right to the edge of the Filchner Ice Shelf, far to the south, and to take readings in the water column there. “This change of plans gave us the first-ever opportunity to take readings on the sea ice so far south in the eastern Weddell Sea – a real premiere,”, says Stefanie Arndt.
During the remainder of the cruise, the team was able to survey the ice on the Weddell Sea eight more times, including five times in the young, seasonal ice that had formed in the western Weddell Sea. In this region, they also launched two survey flights with the helicopter and the sea-ice thickness sensor EM-Bird. “This new data is extremely valuable for us, since we have virtually no comparison data from the region for this time of year. We hope to be able to return here next year – but that makes the data we gathered this time all the more important,” enthuses Stefanie Arndt (Photos 1 and 2).
Photo 1: Group selfie on the Antarctic pack ice. AWI sea-ice physicist Stefanie Arndt (left) and her team during Polarstern expedition PS 146. Photo: Stefanie Arndt / Alfred Wegener Institute.
Photo 2: From the surface of the sea ice, two researchers film the sea-ice thickness survey flight of Polarstern’s onboard helicopter. It hauls the sea-ice thickness sensor “EM-Bird” low over the Antarctic sea ice. Photo: Stefanie Arndt / Alfred Wegener Institute.
At each waypoint on the sea ice, the AWI experts deployed sea-ice buoys. You can follow their drift at the Sea Ice Data Portal. Just click on the following and use the menu to select the buoys in the region “Antarctic”. Now click “Refresh” and you’ll see a map of all active sea-ice buoys in the Weddell Sea (Figure 11).
Figure 11: Map of the Antarctic Weddell Sea, showing the journeys of the AWI sea-ice buoys deployed on the current Antarctic expedition PS 146. Map: meereisportal.de.
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