- Antarctica: For the third consecutive winter, exceptionally low sea ice forms during the winter months; satellite data record the third smallest extent since measurements began.
- A new study provides clear evidence of abrupt climate and environmental changes in Antarctica.
- The summer sea-ice melt in the Arctic is moderate but accompanied by extreme marine heat waves across large parts of the Arctic Ocean.
- Sea Ice Portal presents at the 2025 Extreme Weather Congress in Hamburg — visit our booth.
Antarctica: Third consecutive winter with exceptionally low sea ice
Sometimes a wake-up call is needed to pause and reconsider one’s strategy. This applies as well to sea-ice research reporting. August 2025 brought such a wake-up call. Therefore, this sea-ice update starts not with the Arctic as usual, but with a focus on Antarctica.
What happened? Firstly, the extent of Antarctic sea ice in the winter month of August did not increase extensively and in line with the typical winter season growth. The extent rose from 15.95 to 17.49 million square kilometers, an increase of merely 1.54 million square kilometers.
A significantly larger increase would have been necessary to make up for the sea-ice deficit from summer and the first half of winter. Thus, with an average extent of approximately 16.68 million square kilometers, it remains the third smallest August monthly mean since the beginning of Antarctic sea-ice measurements (see Figures 1, 2, 3 & 4).
Figure 1: Development of Antarctic sea-ice extent (blue line) in comparison. The turquoise band indicates the span of minima and maxima in the period 1981 – 2010. The blue curve for 2025 remained well below the turquoise area throughout August. The figures provided reflect the sea-ice extent on 31 August for the respective years. The graphic is a screenshot from the Sea Ice Portal’s interactive annual cycle tool.
Figure 2: Development of mean sea-ice extent in the Antarctic for the month of August. The light blue line represents the long-term trend.
Figure 3: Difference in the mean position of the ice margin in August 2025, compared to the long-term mean for the years 2003 – 2014. Regions marked in blue had more Antarctic sea ice than in the reference period in August 2025; those marked in red had less. The graphic highlights the significant regional differences in Antarctic sea-ice development. While the winter sea ice cover in the Bellingshausen Sea has been steadily declining for over a decade, satellites detected a larger area of pack ice in the Ross Sea in August 2025 compared to the long-term average.
It is particularly important to note that for the third consecutive time, the winter sea-ice extent in Antarctica remains largely far below the range of extent variations known from the reference period 1981 to 2010. This means that there is once again an exceptionally low amount of sea ice — a statement that directly leads into the actual wake-up call.
Figure 4: Air temperature anomalies over Antarctica for August 2025, compared to the long-term mean temperatures during the period 1971–2000. The graphic shows that in the regions where sea-ice extent was lower than the long-term average in August, air temperatures were up to 4 degrees Celsius above normal. This warmth may have contributed to the delayed formation of new sea ice.
Clear signs of abrupt changes in key climate components in Antarctica
In the third week of August, the journal Nature published a study in which an international team of polar researchers presented numerous first-ever pieces of evidence for rapid, interconnected changes in key climate components in Antarctica. In addition to changes in the Antarctic ice sheets and ocean circulation, changes in sea-ice cover play a crucial role. The five main findings regarding sea ice are summarized as follows:
- The amount of Antarctic sea ice has decreased drastically in recent years. This remarkable decline suggests that either a regime shift towards a new sea-ice state is underway or that existing satellite records are insufficient to fully capture the natural variability of sea ice. Scientific reconstructions of sea-ice cover over the past 100 years or more show that the recent ice loss is exceptional.
- The increase in Antarctic sea ice up to 2014 was characterized by strong regional compensation where areas of expansive sea ice, to some degree, balanced concurrent areas of reduced sea ice. Regional variability remains an important characteristic of Antarctic sea ice but this regional variability has been occurring in a declining mean state over the past decade.
- Since 2016, thinning of Antarctic winter sea ice has resulted in earlier retreat that has increased ocean surface warming and delayed the formation and thickening of sea ice the following winter. This self-reinforcing process highlights the connection between recent sea-ice decline in Antarctica and ocean warming.
- Antarctica could become largely ice-free in summer earlier than the Arctic.
- Emperor penguins depend largely on stable, land-fast sea ice (so-called fast ice) from March/April to January for breeding (Figure 5). Many regions with previously multi-year fast ice are now transitioning to seasonal fast ice — that is, the ice breaks up in summer. This trend is expected to continue, putting emperor penguins at risk of extinction by 2100.
Figure 5: Emperor penguins breed on so-called fast ice, which refers to sea ice that is frozen solidly along the coastline. Due to current climate changes, this ice is breaking up more frequently and earlier in the year, causing the colonies to lose their chicks and increasing the risk of extinction for these magnificent birds. (Photo: Alfred Wegener Institute / Mario Hoppmann)
The authors demonstrate for the first time that we now see clear changes in all the dominant components of the Antarctic system—and all these changes point in the same direction. They go hand in hand. Therefore, we can firmly conclude that the interaction between sea ice, glaciers, ocean, climate, and the biosphere in the Antarctic region is currently undergoing a fundamental transformation. The system is experiencing a regime shift, meaning it is transitioning into a new state
However, interpreting the current sea-ice developments in Antarctica as additional evidence for these profound system changes remains difficult: “The extent of Antarctic winter sea ice has declined sharply for four years. The data from the winter of 2025 confirms this trend. Yet, this period is far too short to exclude natural fluctuations within the ice-ocean-climate system as a cause of the decline. In contrast, we have seen a clear decrease in summer sea-ice extent for about ten years. Based on these data, it is somewhat easier to speak of fundamental changes, though even ten years is still not a climatologically relevant period,” explains the scientist.
Figure 6: AWI sea-ice physicist and Antarctica expert professor Stefanie Arndt. She is currently coordinating the preparation of the international Antarctic research initiative “Antarctica InSync.” As part of this programme, researchers will study sea ice, ocean, and atmosphere in various regions of the Southern Ocean for one year. (Photo: Alfred Wegener Institute / Stefanie Arndt)
Tasks for Science
The new study presents many challenges for polar researchers worldwide: “For example, it emphasizes that we still know very little about the development of sea-ice thickness in Antarctica. Parameters such as ice thickness, the surface structure of the pack ice, and the snow cover height are extremely important for making statements about the mass balance and lifespan of the sea ice,” says Stefanie Arndt.
Moreover, the new scientific article shows that Antarctic research must investigate and evaluate environmental changes in Antarctica in a much more interdisciplinary manner. “We need stronger integration across different disciplines, and as sea-ice researchers, we must more often ask what implications the observed changes in pack ice have for the ocean, large ice shelves, and the ice sheets behind them. The fact is: if the regime changes, science must also focus much more on the interplay of all components,” concludes the AWI expert.
Arctic: Moderate melting and extremely warm sea surfaces
While the sea-ice development in the Southern Ocean remains well below the normal variability range, this year's summer sea-ice melt in the Arctic is less dramatic. During August, the sea-ice extent decreased from 6.28 million square kilometers to 4.95 million square kilometers. The monthly average was 5.51 million square kilometers and corresponds to the tenth-smallest average for this season since the beginning of satellite measurements, similar to the year 2023. The sea-ice extent curve stayed at all times within the range of averaged minimum and maximum values from the comparison period 1981 to 2010 (Figure 7). "Based on the current development, we expect a similar September sea-ice minimum as last year," says Dr Klaus Grosfeld, an expert from the Sea Ice Portal.
Figure 7: Development of Arctic sea-ice extent (blue line) in comparison. The turquoise band indicates the span of minima and maxima in the period 1981 – 2010. The blue curve for 2025 remained within the turquoise area every day throughout August.
With concern, Klaus Grosfeld and other experts look at the currently very warm sea surface temperatures in nearly all marginal areas of the Arctic Ocean (Figure 8).
“Over the course of the summer, the sea surface has warmed unusually strongly over extensive areas of the Arctic Ocean. We observe this warming signal from the Greenland Sea across the Barents and Kara Seas to the Russian marginal seas. Additionally, the entire North Pacific and the Chukchi Sea are also significantly warmer than in previous years and the record minimum year of 2012,” explains Klaus Grosfeld.
The exceptional sea-surface temperatures are consistent with atmospheric temperature developments. In August 2025, the air masses over large parts of the European and West Siberian Arctic were 4 to 8 degrees Celsius warmer than the long-term average for 1971–2000 (Figure 9).
Over the Canadian Basin, however, the air at about 760 meters altitude was up to 4 degrees Celsius cooler, which may explain why more pack ice survived in this part of the Arctic Ocean in August compared to last year and the long-term average (Figure 10).
Figure 8: Sea-surface temperature anomalies for August 2012 and August 2025 compared to the reference period 1971–2000. It can be seen that in August 2025, especially the North Pacific and the Chukchi Sea were significantly warmer than in the record minimum year 2012.
Figure 9: Air temperature anomalies over the Arctic in August 2025 compared to the long-term average temperatures during the period 1971–2000.
Figure 10: Difference in the mean position of the ice margin in August 2025, compared to the long-term mean for the years 2003-2014. Areas marked in blue indicate sea regions where more Arctic sea ice existed in August 2025 than in the previous year. This was only the case in the Canadian Basin. Regions marked in red, on the other hand, had less sea ice.
The extreme sea temperatures have a significant impact on both the thickness and melting of existing sea ice. Additionally, they can delay new sea-ice formation towards the end of summer. “The current marine heatwave particularly affects the Russian marginal seas, which are an important nursery for Arctic sea ice. Over the coming weeks and months, we will closely monitor how long this warmth persists and what effect it will have on new ice formation,” says Klaus Grosfeld.
Sea Ice Experts at the 15th Extreme Weather Congress in Hamburg
The exceptional warming of the Arctic marginal seas and its consequences for sea ice will be two of several key topics discussed by experts from the Sea Ice Portal at the 15th Extreme Weather Congress in Hamburg. The congress will take place from September 24 to 25 at HafenCity University. Among those attending will be AWI se- ice physicist Dr Luisa von Albedyll, Sea Ice Portal co-founder Dr Klaus Grosfeld and Dr Renate Treffeisen, as well as Dr Marcel Nicolaus, chief scientist of this year’s summer Arctic expedition of the research icebreaker Polarstern (CONTRASTS 2025) via live link. Visit us at the Sea Ice Portal booth and engage with us!
Figure 11: Photograph of the research icebreaker Polarstern during this year’s summer Arctic expedition CONTRASTS, whose most important interim results will be presented in the September update. (Photo: Alfred Wegener Institute / Stefanie Brechtelsbauer)
Contact
Prof. Dr. Stefanie Arndt (AWI)
Questions?
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Author
Sina Löschke (Science Writer)
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