Northern Hemisphere Sea Ice extent
Total sea ice extent on the northern hemisphere during the past years, including climate mean; plus/minus 2 standard deviations.
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.
We have improved the algorithms calculating sea ice concentration and extent. Consequently, on June 28, 2016, we updated the graphs of ice extent with new data of higher quality. In particular, calculation of ice concentration in coastal zones have been improved, but also calculation of ice concentration in the Arctic ocean is improved with this new setup.
The sea ice extent data from 1979 till today is composed by a Climate Data Record (CDR, OSI-409a), an Interim CDR providing updates with one month delay to the CDR (ICDR, OSI-430) and an operational setup that calculates sea ice extent for the period between the ICDR and today. Further, the algorithms behing these three products are now more consistent than the previous processing chain.
This switch to new algorithms has led to small changes in the trends of sea ice extent since the first year of the data set, but it has not changed the general picture of ice extent decline.
You can read technical and validation reports of the products here.
Sea ice extent in recent years for the northern hemisphere.
The grey shaded area corresponds to the climate mean
plus/minus 2 standard deviations.