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Version information

June 2019: The sea-ice extent time-series plots on this page are all based on our Sea Ice Concentration Climate Data Records v2 (OSI-450, OSI-430-b) (see Documentation section below).
Previous versions of these plots, using our v1 climate data records, are still available here.

Daily updated Sea Ice Extent Trackers

Northern Hemisphere
Southern Hemisphere

Seasonal (monthly averaged) Sea Ice Extent.

Northern Hemisphere
Southern Hemisphere

Monthly (last month) Sea Ice Extent.

Northern Hemisphere
Southern Hemisphere

Monthly Sea Ice Extent

Display sea ice extent trend for chosen month.
Month:

Northern Hemisphere
Southern Hemisphere

Documentation

Definitions

Sea Ice Extent (SIE) is defined as the area covered by a significant amount of sea ice, that is the area of ocean covered with more than 15% Sea Ice Concentration (SIC). Sea Ice Area (SIA) is the total ocean area covered by any amount of ice.
Sea Ice Concentration is the fractional coverage of a grid cell that is covered with sea ice.
At hemispherical scales, SIE is often reported with units of 10^6 sq km (millions square kilometers).

Input Data

The EUMETSAT OSISAF sea-ice extent and area are computed from three SIC products:The links above provide full documentation on the algorithms and processing details for these products, as well as URLS to access the SIC data, and to visualize examples maps of the products.
All our SIC products are based on passive microwave sensors. The CDR uses data from the SMMR, SSM/I, and SSMIS instruments, while the ICDR and NRT products are using SSMIS only.
Atmospheric fields of wind speed, water vapour and 2m temperature are used as well, all from the ECMWF, both from re-analysis (ERA-Interim), and operational forecasts.

Methodology

Daily SIE values

Daily SIE values are computed from the daily SIC maps. All sea-ice covered ocean is included, lake ice is not. SIE is computed as the sum of the area of the grid cells that have a SIC value larger than 15%. SIA is the sum of the area of all grid cells that have a SIC value larger than 15%, weighted by the SIC value.
In the daily SIE and SIA time series, the CDR is always used from Jan 1979 to Dec 2015, then the ICDR from Jan 2016 onwards. The last 15 days of the time series are always from the NRT SIC product.
Validation experiments conducted at the OSISAF documented that all three SIC products are consistent each others.
The daily values are plotted as-is, without interpolation nor running-mean average.

Monthly SIE values

The OSISAF Monthly SIE and SIA values are computed as averages of the daily SIE values.

Trends and reference period

All the trends are from least-square linear regression, with no consideration for statistical correlations between the points along the time series. As for all trends, they describe the past changes, but should be used with caution when predicting future evolution. The linear rate of change in SIE is always indicated as thousands km per year, to be easily comparable with the values at the NSIDC SII.
The same rate of change are also reported as percentage change per decade, relative to a base period. The base period is 1981-2000, again to ease comparison with NSIDC SII.

Difference to older version

An earlier version of these graphs was available until June 2019. The main difference was in the input data used.
Input data for the earlier version of the graphs was: