From Science Matters
By Ron Clutz
July 2025 was the final report of the Sea Ice Prediction Network (SIPN) before the actual September monthly extent is reported by NOAA Sea Ice Index (SII). The report (link in red) gave this overview.
2025: July Report from Sea Ice Prediction Network
The July 2025 Outlook received 22 pan-Arctic contributions (Figure 1). This year’s median forecasted value for pan-Arctic September sea-ice extent is 4.27 million square kilometers with an interquartile range of 4.13 to 4.54 million square kilometers. This is lower than observed in 2023 (4.37 million square miles) and 2024 (4.35 million square miles) observed in September. The lowest sea-ice extent forecast is 3.38 million square kilometers, from Sun, which would be a new record low for the satellite period (1979-present); the highest sea-ice extent forecast is 5.17. . . The observed extent values are from the NSIDC Sea Ice Index (Fetterer et al., 2017), based on the NASA Team algorithm sea ice concentration fields distributed by the NASA Snow and Ice Distributed Active Archive Center (DAAC) at NSIDC (DiGirolamo et al., 2022; Meier et al., 2021).
These are predictions as of August 20 for the September 2025 monthly average ice extent reported by NOAA Sea Ice Index (SII). This post provides a look at the 2025 September monthly averages comparing MASIE and SII datasets. (19 year average is 2007 to 2025 inclusive).
SIP network predicted SII would be 4.27M km2, and the actual result is 4.7M, while MASIE reported 5.0M km2.
The table below provides the monthly Arctic ice extent averages for comparisons (all are M km2)
| Monthly | MASIE 2025 | SIIv.4 2025 | MASIE -SII | MASIE-19yr AVE | SIIv.4-19yr AVE |
| Jan | 13.206 | 13.131 | 0.075 | -0.583 | -0.470 |
| Feb | 13.802 | 13.745 | 0.057 | -0.878 | -0.715 |
| Mar | 14.274 | 14.140 | 0.134 | -0.587 | -0.545 |
| Apr | 13.846 | 13.910 | -0.063 | -0.249 | -0.109 |
| May | 12.497 | 12.559 | -0.062 | -0.119 | -0.108 |
| June | 10.510 | 10.485 | 0.025 | -0.306 | -0.388 |
| July | 7.942 | 7.660 | 0.282 | -0.345 | -0.375 |
| Aug | 5.854 | 5.395 | 0.459 | -0.020 | -0.220 |
| Sept | 4.990 | 4.745 | 0.245 | 0.298 | 0.050 |
The first two data columns are the 2025 YTD shown by MASIE and SII, with the MASIE surpluses in column three. Column four shows MASIE 2025 compared to MASIE 19 year averages, while column five shows SII 2025 compared to SII 19 year averages.
MASIE started the year in deficits to average but recovered in spring to virtually match average in August, and now 298k km2 above average. SII was below its averages throughout and much lower than MASIE in July, and in August down by nearly half a Wadham. That gap reduced to -245k km2 in September.
Current Arctic Ice Extent Conditions
The month of September shows the annual dip in arctic ice extents, then recovering to end slightly higher than the beginning. Note MASIE 2025 started 170k km2 above average and ended 316k in surplus. SII v.4 began 319k km2 in deficit to MASIE and ended 153k lower.
The table below shows the distribution of ice over the Arctic regions ofr yesterday September 30, 2025, in comparison with the MASIE average and some other years of note.
| Region | 2025273 | Day 273 ave. | 2025-Ave. | 2007273 | 2025-2007 |
| (0) Northern_Hemisphere | 5265296 | 4947157 | 318139 | 4086883 | 1178413 |
| (1) Beaufort_Sea | 567776 | 546476 | 21301 | 498743 | 69033 |
| (2) Chukchi_Sea | 382991 | 220747 | 162244 | 51 | 382940 |
| (3) East_Siberian_Sea | 502004 | 299345 | 202660 | 311 | 501693 |
| (4) Laptev_Sea | 229451 | 168694 | 60758 | 235245 | -5793 |
| (5) Kara_Sea | 992 | 36279 | -35287 | 15367 | -14375 |
| (6) Barents_Sea | 0 | 13476 | -13476 | 4851 | -4851 |
| (7) Greenland_Sea | 170295 | 239645 | -69350 | 353210 | -182915 |
| (8) Baffin_Bay_Gulf_of_St._Lawrence | 77930 | 55264 | 22665 | 42247 | 35682 |
| (9) Canadian_Archipelago | 379648 | 370610 | 9038 | 307135 | 72513 |
| (10) Hudson_Bay | 5071 | 3054 | 2017 | 1936 | 3135 |
| (11) Central_Arctic | 2947568 | 2992334 | -44766 | 2626511 | 321057 |
The massive surpluses in Eurasian basins of Chukchi, E. Siberian and Laptev more than offset smaller deficits in Atlantic basins Kara and Greenland seas. The over surplus was 318k km2 or 6.4%, and exceeded 2007 by 1.2 wadhams of ice extents.
Summary
The experts involved in SIPN are expected SII 2025 September to be somewhat lower than recent years, but Arctic ice extents exceeded the 19-year averages.
Footnote:
Some people unhappy with the higher amounts of ice extent shown by MASIE continue to claim that Sea Ice Index is the only dataset that can be used. This is false in fact and in logic. Why should anyone accept that the highest quality picture of ice day to day has no shelf life, that one year’s charts can not be compared with another year? Researchers do this, including Walt Meier in charge of Sea Ice Index. That said, I understand his interest in directing people to use his product rather than one he does not control. As I have said before:
MASIE is rigorous, reliable, serves as calibration for satellite products, and continues the long and honorable tradition of naval ice charting using modern technologies.
More on this at my post Support MASIE Arctic Ice Dataset
MASIE: “high-resolution, accurate charts of ice conditions”
Walt Meier, NSIDC, October 2015 article in Annals of Glaciology.
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