Version information

September 2020, introducing v2p1: 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 (v2) are still available here.

Daily updated Sea Ice Extent

Northern Hemisphere Southern Hemisphere

All months since 1979

Northern Hemisphere Southern Hemisphere

Trend for last month

Northern Hemisphere Southern Hemisphere

Trend for current month

Northern Hemisphere Southern Hemisphere

Rank of monthly sea ice extent

Northern Hemisphere Southern Hemisphere

Data

  Daily values Monthly values
Northern Hemisphere txt  /  nc txt  /  nc
Southern Hemisphere txt  /  nc txt  /  nc
Global txt  /  nc txt  /  nc
Svalbard txt  /  nc txt  /  nc
Barents Sea txt  /  nc txt  /  nc

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 (0% SIC threshold).

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 "v2" Climate Data Record (CDR), covering Jan 1979 to Dec 2015 (OSI-450)
  • The "v2" Interim Climate Data Record (ICDR), starting in Jan 2016, with a 16 days latency (OSI-430-b);
  • A Near-Real-Time (NRT) product that use the same processing chain as OSI-450 and OSI-430-b, always up-to-date to the previous day.

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 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 0%, 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.

On days when SIC data are missing, SIE and SIA values are linearly interpolated from the neighbours. The interpolation is not conducted if more than 5 consecutive days are missing. 

Monthly values

The OSISAF monthly SIE and SIA values are computed as averages of the daily SIE values, also using the interpolated daily 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 1981-2010.

Difference to older version

An earlier version of these graphs (v2) was available until September 2020. The main difference with v2p1 are:

  • v2 had no temporal interpolation of missing values;
  • v2 used 1981-2000 as a reference period;
  • the outlook of the graphs.
  • filename and directory structure to find the files on our website.