The Sea Ice Index provides a quick look at Arctic- and Antarctic-wide changes in sea ice area. It is a source for consistent, up-to-date sea ice area from November 1978 to the present. Monthly data and images are available via Sea Ice Index Web site (http://nsidc.org/data/seaice_index/index.html). The covered area excludes the area not imaged by the sensor. This area is 1.19 million square kilometers for SMMR (from the beginning of the series through June 1987) and 0.31 million square kilometers for SSM/I (from July 1987 to present). Therefore, there is a discontinuity in the "area" data values in this file at the June/July 1987 boundary.