Sea Ice Index

Documentation

Sea ice is one of the iconic indicators of climate change. It is monitored routinely using satellite data since the late 1970s, although some earlier satellite observations exist, and ship observations and proxies can be used in some regions since as early as 1850.

On this page, we gather MET Norway’s contribution to monitoring sea-ice cover using a variety of satellite sources, that cover both global (Northern and Southern Hemispheres) and regional areas (e.g. Svalbard and the Barents Sea). Some of these plots are produced in operational services where MET Norway collaborates with other projects, such as the EUMETSAT OSI SAF, ESA CCI, the EU Copernicus Services (CMEMS and C3S), and for the ice charts the U.S. NIC and Russian AARI.

Definitions

• Sea Ice Concentration (SIC) is the fractional coverage of a grid cell that is covered with sea ice. It is also called the sea-ice area fraction.

• Sea Ice Extent (SIE) is defined as the area covered by a significant amount of sea ice. For the passive microwave data records a commonly used definition is the area of the ocean covered with more than 15% Sea Ice Concentration. For the ice charts, the threshold is 10%. 

• Sea Ice Area (SIA) is the total area covered by any amount of ice (0% SIC threshold). It is generally less than SIE. See also the relevant FAQ at NSIDC here.

• At hemispherical scales, SIE and SIA are often reported with units of 10^6 sq km (millions square kilometers).

• Our climatological reference period is 1981-2010.

Input Data

Sea-ice concentration data used in our sea-ice indicators are from two sources:

1. The archive of navigational sea-ice charts at MET Norway, dating back to 1967 and covering the European Arctic domain. An area around Svalbard (0 – 40°E, 72 – 85°N) is extracted to build the Svalbard indicators shown here.

2. The EUMETSAT OSI SAF Sea Ice Index - consisting on sea-ice extent and area, is computed from three SIC products:

• The "v3" Climate Data Record (CDR), covering October 1978 to Dec 2020 (OSI-450-a);
• The "v3" Interim Climate Data Record (ICDR), starting in Jan 2021, with a 16 days latency (OSI-430-a).

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 OSI SAF 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.

Version information for OSI SAF Sea Ice Index

July 2023, introducing v2.2: The OSI SAF Sea Ice Index (v2.2) on these pages are all based on our Sea Ice Concentration Climate Data Records v3 (OSI-450-a, OSI-430-a) (see Input Data section above). 

For more information on the development, method, and documentation of the EUMETSAT OSI SAF Sea Ice Index, see OSI SAF web-page.