In 2026, the Arctic winter sea-ice extent (annual maximum extent , note 1 ) reached the lowest value since satellite observations began in 1979 (Figure 1a), following the previous record low in March 2025.
As part of the Arctic Challenge for Sustainability III (ArCS III, note 2 ), the National Institute of Polar Research (NIPR) and the Japan Aerospace Exploration Agency (JAXA) maintain a long-term dataset spanning more than 40 years. This dataset is primarily based on observations from microwave radiometers, including the Advanced Microwave Scanning Radiometer 2 (AMSR2) onboard the Global Change Observation Mission – Water "SHIZUKU" (GCOM-W). The institutions contribute to monitoring polar environmental changes by visualizing temporal and spatial changes in sea ice extent in the Northern and Southern Hemispheres and making the data available on the Arctic Data archive System (ADS, note 3 ) website.
Overview of Arctic Winter Sea-Ice Extent in 2026
The Arctic sea-ice extent generally increases from October to March and decreases from April to September. During the winter of 2025–2026, sea-ice extent remained relatively low compared to the 2010s average (orange thick line and black dashed line in Figure 1b). As a result, the sea-ice extent reached its annual maximum of 13.76 million square kilometers on March 13. This value was about 0.03 million square kilometers smaller than the previous record set in 2025, making it the lowest winter extent in the satellite record (orange and blue thick lines in Figure 1b).
Factors Behind Record Low Arctic Winter Sea-Ice Extent and Marked Changes in the Sea of Okhotsk
A comparison of the sea-ice edge on March 13, 2026 (boundary between white and blue areas in Figure 2a) with the 2010s mean (brown lines) shows that the sea-ice extent remained low in the Sea of Okhotsk. The southward expansion of sea ice was also limited in the Baffin Bay–Labrador Sea, located between Greenland and Canada.
Detailed analysis indicates that from January to February 2026, temperatures in the Sea of Okhotsk and in the Baffin Bay - Labrador Sea region remained higher than average (Figure 2b), hindering the southward expansion of sea ice. Furthermore, in the Sea of Okhotsk, easterly to southeasterly winds prevailed from mid-February to mid-March, and temperatures were higher than those during the same period in 2025. As a result, the sea ice extent in the Sea of Okhotsk began to decrease after February 19, which served as a major factor limiting the overall expansion of Arctic sea ice.
Future Changes in the Arctic and Sea-Ice Observations
AMSR2 has been in operation for more than 13 years, and preparations are underway for the public release of data from the latest sensor of the AMSR series, the Advanced Microwave Scanning Radiometer 3 (AMSR3, note6 ). Figure 3 shows the sea-ice distribution derived from observations by AMSR3 onboard the Global Observing SATellite for Greenhouse gases and Water cycle "IBUKI GW" (GOSAT-GW), which was launched on June 29, 2025, and is currently undergoing calibration and validation. AMSR3 provides data quality comparable to that of AMSR2. Sea ice is a critical component of the climate system; its fluctuations can impact extreme weather patterns and marine environments. There are concerns that Arctic sea ice changes may reach a point of no return amid progressing global warming, potentially triggering a chain of impacts across the global climate system ( note7 ). In addition to sea ice, AMSR3 can detect snowfall, enabling more comprehensive analyses of the Arctic environment. The data are scheduled to be publicly available in the summer of 2026. We will continue to advance sustained monitoring, detailed analyses, and the dissemination of information using satellite-based microwave radiometer observations, including AMSR3.
Note
Note 1. Sea-ice extent
Sea-ice extent is defined as the area where sea-ice concentration (the fraction of a pixel covered by sea ice) is at least 15%. In this article, Arctic sea-ice extent includes not only the Arctic Ocean but also surrounding regions such as the Sea of Okhotsk, the Bering Sea, the Labrador Sea, Baffin Bay, and Hudson Bay. The values presented here are based on a five-day average. For details on the calculation method of sea-ice extent, please refer to https://ads.nipr.ac.jp/vishop/#/dataset .
Note 2: Arctic Challenge for Sustainability III (ArCS III)
Launched in April 2025, ArCS III is Japan's national Arctic research project led by the National Institute of Polar Research as the representative institution, with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Hokkaido University serving as deputy representative institutions. It is also one of Japan's Arctic policies, promoted by the Headquarters for Ocean Policy at the Cabinet Office. The project goal is "To create integrated knowledge that contributes to solving the social challenges arising from environmental and societal changes in the Arctic." Here, "integrated knowledge" refers to combining insights from different academic fields - natural sciences, social sciences, and the humanities - to approach complex challenges from multiple perspectives. The aim is not only to link disciplines but also to generate knowledge that can inform real-world solutions through collaboration among researchers and with local communities. The project is scheduled to run for five years, until March 2030 .
Note 3: The Arctic Data archive System (ADS)
A data archive system for preserving and managing observation data and model simulation products obtained in the Antarctic and Arctic regions through the GRENE Arctic Climate Change Research Project (2011–2016), Arctic Challenge for Sustainability (ArCS, 2015–2020), Arctic Challenge for Sustainability II (ArCS II, 2020–2025), and Arctic Challenge for Sustainability III (ArCS III, 2025–2030)
Note 4. Arctic and Antarctic sea-ice information in February 2026
https://asic.nipr.ac.jp/e/info/2026-03-09-01/
Note 5. NCEP-NCAR Reanalysis 1
Atmospheric reanalysis data produced by the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR).
https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html (Kalnay et al., The NCEP/NCAR 40-year reanalysis project, Bull. Amer. Meteor. Soc., 77, 437-470, 1996).
Note 6: AMSR3
Onboard the GOSAT-GW satellite, currently undergoing calibration and validation. Routine operations began in October 2025.
https://www.eorc.jaxa.jp/AMSR/satellite/gosat-gw_en.html
Note 7. IPCC (2021)
IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2391 pp. doi: 10.1017/9781009157896 .
Reference
Kalnay et al., The NCEP/NCAR 40-year reanalysis project, Bull. Amer. Meteor. Soc., 77, 437-470, 1996
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