NOAA@NSIDC, National Snow and Ice Data Center (CIRES, University of Colorado Boulder)
Sea Ice Index, Version 4 (G02135)
Sea ice extent (area of ocean with at least 15% ice concentration) and sea ice area, in million km2, for the Northern and Southern Hemispheres, from passive microwave satellite data on a 25 km grid: every other day from 26 October 1978 to 20 August 1987, daily after that (no data from 3 December 1987 to 13 January 1988). Daily files carry extent and a 1981-2010 daily climatology (mean, standard deviation and percentiles); monthly files give one value per year for a calendar month. From 1 January 2025 the input is JAXA's AMSR2 (NSIDC-0803) instead of the DMSP SSMIS record (NSIDC-0051), which the source column of each row records. Recent daily values are revised for a day or two. Not interchangeable with OSI SAF's index, which uses a different algorithm; the two are shown as separate lines.
Numbers published from it
Licence and credit
- What the terms say
“As a condition of using these data, you must cite the use of this data set. Such a practice gives credit to data set producers and advances principles of transparency and reproducibility.”
From the producer's terms, checked 2026-10-04; re-checked automatically every week.
- Credit we give
- Fetterer, Knowles, Meier, Savoie, Windnagel & Stafford (2025), Sea Ice Index, Version 4 (G02135), National Snow and Ice Data Center, Boulder, Colorado, doi:10.7265/a98x-0f50, accessed {date_accessed}.
- Copy of the raw file
- Allowed: we keep a public copy of every version we use.
- Cite as
- Fetterer, F., Knowles, K., Meier, W. N., Savoie, M., Windnagel, A. K. & Stafford, T. (2025). Sea Ice Index. (G02135, Version 4). [Data Set]. Boulder, Colorado USA. National Snow and Ice Data Center. https://doi.org/10.7265/a98x-0f50. Daily and monthly sea ice extent, Northern and Southern Hemispheres. Date Accessed {date_accessed}.
Files
Arctic daily extent and missing area (million km2) from 26 October 1978, with the input files of each day's 3-day window in the last column. Two header rows.
https://noaadata.apps.nsidc.org/NOAA/G02135/north/daily/data/N_seaice_extent_daily_v4.0.csvArctic 1981-2010 daily climatology by day of year: average extent, standard deviation and 10th, 25th, 50th, 75th and 90th percentiles (million km2).
https://noaadata.apps.nsidc.org/NOAA/G02135/north/daily/data/N_seaice_extent_climatology_1981-2010_v4.0.csvAntarctic daily extent and missing area (million km2) from 26 October 1978, same layout.
https://noaadata.apps.nsidc.org/NOAA/G02135/south/daily/data/S_seaice_extent_daily_v4.0.csvAntarctic 1981-2010 daily climatology by day of year, same layout.
https://noaadata.apps.nsidc.org/NOAA/G02135/south/daily/data/S_seaice_extent_climatology_1981-2010_v4.0.csvArctic March (around the yearly maximum) extent and area by year from 1979 (million km2).
https://noaadata.apps.nsidc.org/NOAA/G02135/north/monthly/data/N_03_extent_v4.0.csvArctic September (around the yearly minimum) extent and area by year from 1979 (million km2).
https://noaadata.apps.nsidc.org/NOAA/G02135/north/monthly/data/N_09_extent_v4.0.csvAntarctic February (around the yearly minimum) extent and area by year from 1979 (million km2).
https://noaadata.apps.nsidc.org/NOAA/G02135/south/monthly/data/S_02_extent_v4.0.csvAntarctic September (around the yearly maximum) extent and area by year from 1979 (million km2).
https://noaadata.apps.nsidc.org/NOAA/G02135/south/monthly/data/S_09_extent_v4.0.csv
Status
- Programme
- Updated daily (the 4 October 2026 file runs to 3 October). The landing page says the data set was "recently downgraded to a 'Basic' Level of Service" because of funding limitations: data integrity is still verified, but support is limited. Funded by NOAA; Version 4 (released July 2025) moved to AMSR2 input from 1 January 2025.
- Updates
- Daily (monthly files after each month ends)
- Last check
- Fetched (2026-10-05T11:04:26Z)
- Independent sources measuring the same thing
- EUMETSAT OSI SAF Sea-Ice Index v3.0 (OSI-420-a)