The following images show a representation of sea ice concentrations for the earth's northern hemisphere and are loaded from the University of Illinois at Urbana-Champaign Polar Research Group's "The Cryosphere Today" website.
The image on the left represents a data point for this day in 1980 (should an image not be available for that day, the most recent image before that date is displayed). The image on the right represents today's data point (or yesterdays if today's image is not yet available - check back later).
These images allow a visual comparison of sea ice concentrations. Concentration, in this case, describes the relative amount of area covered by ice, compared to some reference area (625 kilometres). The concentrations are represented as percentages with 0% meaning the reference are contains zero ice and 100% meaning the reference area is completely covered in ice. These percentages are depicted by colour.
It is possible to get an idea of sea ice extent from these images and the difference in extent between the two data points. Please note however that concentrations below 30% are not shown in these images and that the usual representation of sea ice extent includes sea ice concentrations above 15%.
Please also note that the white, snow covered areas are irrelevant and are largely missing from the 1980 image set.
More information on the Cryosphere may be found at the aforementioned website of the Polar Research Group. Further information about sea ice may be found all over the web; particularly:
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