Credit: NSIDC

This video shows the interannual variation of the September sea ice concentration from the start of the satellite record in 1979 to 2008. The pink line shows the average September sea ice extent from 1979-2000, which is taken as the climatological base period. Towards the end of the video, the decline in the summer sea ice extent is clearly visible, with large open water areas in September that used to be covered by sea ice.