1 90 0 8000000 September Mean Sea Ice Concentration, 1979-2004 Sea ice is frozen seawater floating on the surface of the ocean. Some sea ice is permanent, persisting from year to year, and some is seasonal, melting and refreezing from season to season. Because the extent of the sea ice is important both for the Arctic marine ecology and for the role it plays in the Earth's climate, understanding the variation of this extent during the year and from year-to-year is vital. Each year, the minimum sea ice extent in the northern hemisphere occurs at the end of summer, in September. By comparing the extent of the sea ice in September over many successive years, long term trends in the polar climate can be assessed. This animation shows the mean sea ice concentration in the northern hemisphere in September between 1979 and 2004. Since 1999, this minimum has shown an ice extent that is consistently 10% to 15% smaller than the average extent over the past 20 years. Animation (600x200) This animation shows the mean sea ice concentration in the northern hemisphere during September between 1978 and 2004. 1 0 1979-09-01 2005-09-01 1979-09 1 1 1979-09-01 1980-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0001.png 24.1 90 -180 180 1980-09 1 1 1980-09-01 1981-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0002.png 24.1 90 -180 180 1981-09 1 1 1981-09-01 1982-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0003.png 24.1 90 -180 180 1982-09 1 1 1982-09-01 1983-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0004.png 24.1 90 -180 180 1983-09 1 1 1983-09-01 1984-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0005.png 24.1 90 -180 180 1984-09 1 1 1984-09-01 1985-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0006.png 24.1 90 -180 180 1985-09 1 1 1985-09-01 1986-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0007.png 24.1 90 -180 180 1986-09 1 1 1986-09-01 1987-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0008.png 24.1 90 -180 180 1987-09 1 1 1987-09-01 1988-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0009.png 24.1 90 -180 180 1988-09 1 1 1988-09-01 1989-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0010.png 24.1 90 -180 180 1989-09 1 1 1989-09-01 1990-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0011.png 24.1 90 -180 180 1990-09 1 1 1990-09-01 1991-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0012.png 24.1 90 -180 180 1991-09 1 1 1991-09-01 1992-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0013.png 24.1 90 -180 180 1992-09 1 1 1992-09-01 1993-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0014.png 24.1 90 -180 180 1993-09 1 1 1993-09-01 1994-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0015.png 24.1 90 -180 180 1994-09 1 1 1994-09-01 1995-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0016.png 24.1 90 -180 180 1995-09 1 1 1995-09-01 1996-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0017.png 24.1 90 -180 180 1996-09 1 1 1996-09-01 1997-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0018.png 24.1 90 -180 180 1997-09 1 1 1997-09-01 1998-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0019.png 24.1 90 -180 180 1998-09 1 1 1998-09-01 1999-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0020.png 24.1 90 -180 180 1999-09 1 1 1999-09-01 2000-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0021.png 24.1 90 -180 180 2000-09 1 1 2000-09-01 2001-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0022.png 24.1 90 -180 180 2001-09 1 1 2001-09-01 2002-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0023.png 24.1 90 -180 180 2002-09 1 1 2002-09-01 2003-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0024.png 24.1 90 -180 180 2003-09 1 1 2003-09-01 2004-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0025.png 24.1 90 -180 180 2004-09 1 1 2004-09-01 2005-09-01 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/SeptMinSeaIce-0026.png 24.1 90 -180 180 Background Image 0 0 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/frames/600x200/background-bluemarble-north.png 24.1 90 -180 180 Legend 1 3 http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003167/iceC_bar.png