Sea ice is frozen seawater floating on the surface of the ocean. Some sea ice is semi-permanent, persisting from year to year, and some is seasonal, melting and refreezing from season to season. The sea ice cover reaches its minimum extent at the end of each summer and the remaining ice is called the perennial ice cover. The 2007 Arctic summer sea ice reached the lowest extent of perennial ice cover on record. The area of the perennial ice has been steadily decreasing since the satellite record began in 1979, at a rate of about 10% per decade. But the 2007 minimum, reached on September 14, is about 38% lower than the climatological average. Such a dramatic loss has implications for ecology, climate and industry.This image compares the difference between the perennial sea ice minimum area on September 14, 2007 and the 1979-2007 average minimum sea ice. A graph inset in the top left corner shows the decline in annual sea ice area from 1979 through 2008. Note: The sea ice image with labels and the graph inset. Data Collected: 2007-09-14, 1979-2007 Average. Animator: Cindy Starr (GST), Greg Shirah (NASA/GSFC). Scientist: Josefino Comiso (NASA/GSFC). Platforms/Sensors/Data Sets: DMSP/SSM/I, Nimbus-7/SMMR, Comiso's September Minimum Sea Ice Concentration.

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