Satellite data show that Arctic sea ice likely reached its annual minimum extent on September 10, 2025. Image courtesy of NASA Earth Observatory created by Lauren Dauphin, using data from the National Snow and Ice Data Center.
We’re looking at the top and bottom of the world this week, specifically at aspects of ice and what’s below it in the Arctic and Antarctica.
Arctic
Last week a report from NASA and the United States National Snow and Ice Data Center indicated that Arctic sea ice reached its likely minimum ice extent for 2025 at 4.60 million square kilometres (1.78 million square miles) on September 10th 2025.
The assessment of sea ice was based on data from the Japan Aerospace Exploration Agency’s Advanced Microwave Scanning Radiometer 2 (AMSR2) satellite. AMSR2 offers global coverage, it has 6 spectral bands and offers two spatial resolutions of 10 square kilometres or 5 square kilometres per pixel, depending on the spectral band.
The minimum figure is assumed as when the sun dips below the Arctic horizon, as falling air temperatures will mean the ice extent begins to grow again. However, it was noted that with areas of low ice concentration remaining, a late-season storm could reduce the sea ice further in coming weeks.
If 10 September is the minimum date, it will mean that 2025 is the joint tenth lowest extent of sea ice, tied with 2008 and 2010, in the almost fifty-year history of satellite measurements. While tenth doesn’t sound too bad, it should be noted that the 19 years between 2007 and 2025 represent the 19 lowest sea ice extents within the records, which is concerning. The lowest figure on record is from 2012, when the minimum ice extent was 3.39 million square kilometres, followed by 2020 when it was 3.82 million square kilometres.
Interestingly, the 2025 figure is higher than the last two years, which saw 4.25 million square kilometres in 2024 and 4.26 million square kilometres in 2023. According to the scientists, while this year had significant melt in the early part of the summer, the melting eased back in early August resulting the slightly higher figures than previous years.
Antarctica
Moving down to the bottom of the Earth and the Antarctic, research published last week in Nature Communications indicates that there are more subglacial lakes beneath Antarctica’s ice than previously believed, which influence glaciers and global sea rise.
The research by Wilson & Hogg et al is titled ‘Detection of 85 new active subglacial lakes in Antarctica from a decade of CryoSat-2 data’, and as the title suggests the team used data from the European Space Agency’s CryoSat satellite in their work. One of the authors, Professor Anna Hogg, also leads the SENSE – Centre for Satellite Data in Environmental Science programme at University of Leeds, and Pixalytics has been involved with the programme over the last five years as we have supported two PhD students.
The team from the University of Leeds, led by Sally Wilson, used 10 years of swath-processed CryoSat-2 satellite radar altimetry data to create a dataset of the thickness of polar sea ice between 2010 and 2020. The team were able to detect localised changes in the height of Antarctica’s icy surface, as the subglacial lakes filled and drained at the base of the ice sheet, meaning that they could detect and map the subglacial lakes. The 85 unknown lakes the team discovered increased the number of known active subglacial lakes by 58%, taking the total now known to 231.
Not all subglacial lakes fill and drain, the largest is Lake Vostok underneath the East Antarctic Ice Sheet, holding an estimated 5000–65 000 cubic km of water. It is believed to be stable, but it is estimated that if it did drain, it would impact ocean circulation, marine habitats, and global sea level.
Conclusion
Exciting to see satellite data being used to track ice extent and discovering new insights into what is sitting beneath the ice.
