Sea Ice Extent Minimum.
The graphics on the right show the mean September sea ice extent on the northern hemisphere.
The plotted values correspond approximately to the sea ice area that 'survived' the summer melt
in the respective years
The graph illustrates a decreasing trend in sea ice extent since 1978, with annual variations
of occationally more than 1 million square kilometres. The 2012 sea ice minimum extented set a new minimum record.
The 2012 September minimum ice extent was only approximately half the mean sea ice extent from the period 1979-2000, - often
referred to as a relative stabil period for the sea ice extent. The blue trend
line in the figure has a negative slope of approximately 60000 km2 per year. The data is provided
by Ocean and Sea Ice Satellite Application Facility (OSISAF)
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.
Mean September sea ice extent in millions of km2 for the northern hemisphere
since 1978. This is a comparable measure to annual minimum sea ice extent.
The black line indicate the decreasing trend in September ice extent.