The archived Sea Ice Index data are numbers and images representing Arctic- or Antarctic-wide monthly sea ice extent, concentration, and anomolies. These numbers and images are derived from passive microwave satellite data as described in the documentation. Daily numbers and images are not archived because day-to-day variability can reflect instrument or processing errors. The monthly data products are a more reliable record of ice variability. Here you can access the monthly Sea Ice Index archives of images and data in various formats.
The ASCII data files tabulate extent and area (in millions of square kilometers) by year for a given month. To access the files, choose a month directory. The files are named N_mm_area.txt (for the Northern Hemisphere where mm is the 2-digit month) and S_mm_area.txt (for the Soutern Hemisphere where mm is the 2-digit month). For example, the file N_04_area.txt contains data from the Northern Hemisphere for the month of April.
Only monthly image files are available in the archive. To access the images, choose a month directory. The files are named H_yyyymm_type.png (where H stands for the hemisphere, yyyy is the 4-digit year, mm is the 2-digit month and type is the type of image in the file). For example, the file S_200303_anom.png is an image of concentration anomalies in the Southern Hemisphere in March 2003.
Monthly sea ice extent shapefiles, November 1978 to present. Shapefiles are available for Northern and Southern hemispheres, both polygons and polylines.
Monthly median shapefiles. Each month's shapefile indicates that month's median extent for the period 1979 to 2000. Shapefiles are available for Northern and Southern hemispheres, polylines only.
Shapefiles are organized in monthly directories, by extent for that month and year or by median extent for that month. Files are zipped. For example, "extent_N_199806_polyline.zip" contains the polyline extent shapefile for the Northern Hemisphere for June 1998.
The Sea Ice Index is derived from the following data sets:
These satellite-derived images depict current sea ice conditions and trends. Long-term changes in Arctic sea ice are an index of climate change. Southern Hemisphere sea ice images are also available. For more information about current conditions and their significance, see Arctic Sea Ice News and Analysis.
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