Cryospheric Climate Indicators in the Arctic

Introduction

Soil Temperature

Snow Cover

Sea Ice

Greenness

Sea Ice Index

Overview | Compare, Animate, or Download Data | Image Derivation  | Interpretation Resources

Overview

In the Northern Hemisphere, sea ice reaches an annual minimum extent in September, and maximum extent in February or (usually) March, although there may be regional variations. The images in the Sea Ice Index data set depict average ice conditions, estimated using satellite passive microwave data for the most recent month available, as well as snapshots of trends and anomalies that compare these recent conditions with the mean for the month.

Please read Image Derivation and Interpretation Resources to understand the uses and limitations of these figures.

Ice Concentration, Last Month

The ice concentration image includes the total area covered by sea ice. This number excludes the open water within the pack, and will therefore always be less than the total extent of the ice.

Anomalies in Extent

Images of anomalies in ice extent show the difference between where the ice edge is on average, and where it is in a particular month. The total extent of sea ice for the month is given.

Trends in Extent

Trends in ice extent anomalies show how the expanse covered by ice is changing from year to year for a given month. Anomalies are given in percentage difference from the mean extent for that month. The mean is calculated using the period 1979-2000.

Anomalies in Concentration

Anomalies in ice concentration show if there is more or less ice for a given month than on average, both regionally (given by the color coding) and for the entire polar sea (given by the total anomaly number).

Trends in Concentration

Images of trends in ice concentration show how the concentration of ice has changed for a given month over the period 1979-2000.

Sea Ice Index References

Meier, W., J. Stroeve, F. Fetterer, K. Knowles. 2005. Reductions in arctic sea ice cover no longer limited to summer. Eos: Transactions of the American Geophysical Society 86, 326.

Fetterer, F., and K. Knowles. 2004. Sea ice index monitors polar ice extent. Eos: Transactions of the American Geophysical Society 85, 163.

User Services

NSIDC strongly encourages you to register as a user of this data product. As a registered user, you will be notified of updates and corrections. When registering, please include the title of this data set, Sea Ice Index.

Acknowledgements

F. Fetterer, K. Knowles, and NSIDC staff developed the Sea Ice Index with financial support from NOAA NESDIS and in cooperation with NOAA NGDC. Please use this citation when referencing the Sea Ice Index:

Fetterer, F., and K. Knowles. 2002, updated 2006. Sea ice index. Boulder, CO: National Snow and Ice Data Center. Digital media.