Monthly average of sea ice concentration as a percentage (e.g., 99.9 =
99.9%). Values under 15% are considered to be open water.

=== Original Data Source ===
Sea Ice Index, Version 3

The Sea Ice Index provides a quick look at Arctic- and
Antarctic-wide changes in sea ice. It is a source for consistent,
up-to-date sea ice extent and concentration images, in PNG format,
and data values, in GeoTIFF and ASCII text files, from November 1978
to the present. Sea Ice Index images also depict trends and
anomalies in ice cover calculated using a 30-year reference period
of 1981 through 2010.
The images and data are produced in a consistent way that makes the
Index time-series appropriate for use when looking at long-term
trends in sea ice cover. Both monthly and daily products are
available. However, monthly products are better to use for long-term
trend analysis because errors in the daily product tend to be
averaged out in the monthly product and because day-to-day
variations are often the result of short-term weather.

Citation:
Fetterer, F., K. Knowles, W. N. Meier, M. Savoie, and A. K.
Windnagel. 2017, updated daily. Sea Ice Index, Version 3.
Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center.
doi: https://doi.org/10.7265/N5K072F8. 2020-08-06.

Citation URL:
https://nsidc.org/data/g02135