idw – Informationsdienst Wissenschaft
Nachrichten, Termine, Experten
Nachrichten, Termine, Experten
idw - Informationsdienst
Wissenschaft
The winter growth period for sea ice in the Arctic Ocean is now over, with levels at a record low. The winter ice extent on 21 March 2025 was lower than at any time since continuous satellite recording began in 1979. At 14.45 million square kilometres, winter sea ice cover is over a million square kilometres below the long-term average. As in February 2025, average Arctic sea ice cover remained at an all-time low for the entire month of March, equalling the previous low set in 2017.
Arctic sea ice follows a seasonal cycle, reaching its maximum winter extent in February and March of each year. As temperatures rise over the course of the year, the sea ice shrinks to its summer minimum in September each year, before falling temperatures induce new ice formation. This year, satellite monitoring identified the lowest maximum winter extent since records began, with just 14.45 million square kilometres of ice cover measured on 21 March 2025. This level is 1.13 million square kilometres below the long-term average for recorded levels in 1981–2010, roughly equivalent in size to the surface area of France and Germany combined.
At 14.21 million square kilometres, the average extent for March also represents a record low, as highlighted in analysis by the Alfred Wegener Institute and the University of Bremen. Only once – in 2017 – has average Arctic sea ice cover reached such low levels since monitoring began in 1979. One obvious cause of this low ice formation is warmer air, with temperatures in the Arctic above the long-term average over winter.
Sub-zero temperatures dominated in the Arctic over winter, causing the ocean water to freeze and form sea ice. In March, however, temperatures reached as high as –10 °C in many areas, which is 9 °C warmer than the long-term average for 1981–2010. “Some of our ice buoys, which drift across the Arctic and transmit data via satellite, recorded temperatures of just –5 °C above the ice at some points during January and February 2025,” reports Dr Thomas Krumpen. The sea-ice physicist at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), offers the following analysis of developments in recent months: “In February, temperatures in some regions reached 16 °C above the past average, as the map of temperature anomalies shows. This will have reduced ice growth in some regions, with this effect evident in modelling and satellite data.”
However, the low sea-ice extent in March can largely be attributed to ice drift. Satellite data for the period from October 2024 to March 2025 shows that strong offshore winds caused by low-pressure areas pushed sea ice from the coast of Russia towards the Central Arctic. “In colder regions, such as the Laptev Sea and Kara Sea, this resulted in above-average formation of new ice, while the ice edge in the warmer Barents Sea shifted northwards,” explains the AWI expert.
Sea-ice formation in the first three months of the year allows specialists at the AWI to make initial cautious estimates of how the Arctic sea-ice situation could develop through to the end of the summer. “There are some indications of a low summer sea-ice extent. In recent months, for example, we’ve observed above-average levels of old and thick sea ice leaving the Arctic through the Fram Strait, presumably as a consequence of unusual drift constellations in previous years,” says Krumpen. The absence of old sea ice impacts the resilience of the remaining sea ice over the summer months. Nevertheless, weather and ocean conditions could still play a significant role in slowing sea-ice melting, with the potential for significant regional variations, and could yet prevent the summer extent dropping below the record low set in 2012. But that doesn’t change anything about the enduring reduction in sea ice levels,” says Krumpen. This is why, in addition to monthly averages, the maximum winter extent and the minimum summer extent, long-term trends provide important insights. This data continues to show a downward trend in ice cover: over the last 40 years, winter sea ice coverage has fallen by roughly 2.5% per decade, attesting to the long-term impact of climate change on Arctic sea ice.
Dr. Thomas Krumpen
+49 (0)471 4831-1753
thomas.krumpen@awi.de
Ice edge Arctic March
sea ice portal
Alfred-Wegener-Institut / sea ice portal
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