Sea ice: compare any two days since 1978
Arctic and Antarctic sea ice on any two days from 26 October 1978 to yesterday, from the NSIDC Sea Ice Index (version 4). NSIDC's own comparison tool was discontinued in October 2025; this board keeps a complete copy of the data, so this one stays.
B =
Point at the map for the details of a spot.
Extent through the year
Clicking the chart sets
As a table
About the data
- Extent is the area of ocean where at least 15% of the surface is ice, cell by 25 km cell; area counts only the ice itself (each cell's area × its concentration). In summer melt ponds make the satellites under-read concentration, so area is the less reliable of the two then.
- Concentration comes from passive microwave radiometers: Nimbus-7 SMMR (1978–87, every other day), the DMSP SSM/I and SSMIS series (1987–), and, in version 4, Japan's AMSR2. A change of instrument is a small step in the record; NSIDC cross-calibrates them.
- The pole hole (grey) is the patch round the North Pole the satellites' orbits never cover. It is counted as ice, as NSIDC does; it shrank with each new instrument.
- There is no data from 3 December 1987 to 12 January 1988 (an instrument failure); before 20 August 1987 there is a map only every other day. The nearest day with data is shown, and the notes say so.
- Single days are noisy (weather moves ice; the sensors mistake storms and wet snow for ice and back). For trends, the 5-day average and monthly values are the ones to trust.
- Ranks and anomalies use NSIDC's official daily extent; the 1981–2010 average and percentiles are NSIDC's. Extents worked out here from the grids agree with NSIDC's to the third decimal place.
- Data: Sea Ice Index, Version 4 (G02135), NSIDC: National Snow and Ice Data Center, Boulder, Colorado; the citation to use is on its page.