9/18/15, "Northern Hemisphere Sea Ice extent," Danish Meteorological Institute, DMI
"Northern Hemisphere Sea Ice extent
Total sea ice extent on the northern hemisphere during the past years,
including climate mean; plus/minus 1 standard deviation.
The ice extent values are calculated
from the ice type data from the Ocean and Sea Ice, Satellite Application Facility
(OSISAF), where areas with ice concentration
higher than 15% are classified as ice.
The total area of sea ice is the sum of First Year Ice (FYI), Multi Year Ice (MYI) and the area
of ambiguous ice types, from the OSISAF ice type product. The total sea ice extent can differ slightly
from other sea ice extent estimates. Possible
differences between this sea ice extent estimate and others are most likely caused by differences in
algorithms and definitions."...