22 September 2011
In case you have not seen this video-
As I mentioned yesterday, the NSIDC put this summer’s minimum of ice as the 2nd lowest on record. When talking about the sea ice, there are three measurements that are most important.
1.Extent and 2. Area are calculated differently and the IARC website describes it very succinctly here:
“The area of sea-ice cover is often defined in two ways, i.e., sea-ice “extent” and sea-ice “area.” These multiple definitions of sea-ice cover may sometimes confuse data users. The former is defined as the areal sum of sea ice covering the ocean (sea ice + open ocean), whereas the latter “area” definition counts only sea ice covering a fraction of the ocean (sea ice only). Thus, the sea-ice extent is always larger than the sea-ice area.: This is the area of ocean covered by at least 15% sea ice.”
There is also the volume (3) of the sea ice. The folks at the Univ. of Washington’s Polar Res. Center have a model called PIOMAS that estimates the volume. Since ice floats and the density is known, the volume can be estimated using the distance above the water surface (freeboard). Cold war submarine data on arctic ice thickness has been very valuable in estimating the long term volume trends. The current estimated loss is -2.8 103 km3/decade.