At the end of each summer, the sea ice cover reaches its minimum extent and the ice that remains is called the perennial ice cover, which consists mainly of thick multi-year ice floes. 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 around Sept. 14, is far below the previous record made in 2005 and is about 38% lower than the climatological average. This data visualization shows the annual sea ice minimum from 1979 through 2007. Waleed Abdalati, head of Goddard's Cryospheric Sciences Branch, said "This year the amount of ice is so far below that of previous years that it really is cause for concern. The trend in decreasing ice cover seems to be getting stronger and stronger as time goes on."