Data & source
Data: NSIDC
Sea Ice Index, Version 4 (G02135) — daily sea ice extent, both hemispheres,
National Snow and Ice Data Center, Boulder, Colorado · freely available and
redistributable with attribution · fetched —.
Scope and gaps, plainly: extent is the area of ocean with at least
15% ice concentration — it measures how far the ice reaches, not how thick it is, so
nothing here describes ice volume. The record runs from 1979, the first full
satellite year; 1978 is two months long and is left out. Before 20 August 1987 the
satellites sampled every other day, and there is a hard gap from 3 December 1987 to
12 January 1988 where a sensor failed — those days are drawn as breaks in the line,
never interpolated. The corridor is the daily minimum, median and maximum across
1981–2010, the reference
period NSIDC itself uses; each baseline year contributes the median of its readings
within one day of the date, so the every-other-day years still fill every column.
The current year is partial and its extreme is labelled "so far" and left out of the
ranking. February 29 exists only in leap years, so its column is thinner than the
rest.