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Exploring the Cryosphere Using Data from the National Snow and Ice Data Center

Access Sea Ice Data (more info) at the National Snow and Ice Data Center (more info)
This webpage was created for SERC by Heather Rissler in consultation with Ruth Duerr and Florence Fetterer, NSIDC.
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The Dataset

Sea Ice image (from the NSIDC). The National Snow and Ice Data Center (more info) (NSIDC) maintains the Sea Ice Index (more info) , which consists of data showing trends and anomalies in monthly mean Arctic and Antarctic sea ice concentration and extent of coverage for a period of record beginning in 1979. Data are obtained from algorithms that convert microwave emission measured by satellites to sea ice concentration and extent data. The data are processed to generate means, trends, and anomalies.

Use and Relevance

"Satellite data indicate that during the past 30 years, annual snow cover in the Northern Hemisphere and Arctic sea ice extent have decreased at a rate of about 3 percent per decade. Are climate changes part of a natural cycle of climate variability? Or are they a result of human influences?" From the NSIDC Cryosphere (more info) webpage.
Sea ice covers millions of square km of the ocean surface, forming and melting during annual cycles. The extent (or coverage) of sea ice has a number of ecological impacts, including regulating heat, moisture, and salinity exchange in the polar oceans; influencing local cloud cover and precipitation; and providing a habitat for polar animals. Scientists use data from the Sea Ice Index to monitor changes in the concentration and coverage of ice in Polar regions. Monitoring these parameters allows scientists to compare changes over time and to uncover temporal trends and anomalies, such as loss of extent over the past 3 decades.

Use in Teaching

This dataset can be used to teach the following topics and skills in cryosperic studies and climate change:

Southern Hemisphere ice concentration for April 2006, showing percentage of coverage


  • Temporal trends in sea ice coverage and concentration, including annual changes and changes over the past three decades
  • Importance of sea ice in arctic ecosystems, including impacts on habitats and livelihood for indigenous peoples
  • The relevance of sea ice formation and melting on ocean circulation
  • Impact of global climate change on sea ice coverage and potential for ocean circulation anomalies
  • Thermodynamics of sea ice formation and melting and contributing factors such as albedo and ocean circulation


Anomalies in Northern Hemisphere Sea ice for the month of April from 1979 to present. Values are presented as a percentage relative to the mean extent.
  • Exploring "balanced reporting" of environmental concerns in the media and how they compare to the scientific method and original context of sea ice data
  • Understanding and practicing statistical tests including averages, means, linear regressions and other models for fitting data, confidence intervals, and trends and anomalies
  • Understanding the methodology of how polar orbiting satellites collect data
  • Understanding spectral properties of various materials at different wavelengths and polarization
  • Understanding how collected data are processed to determine sea ice extent (coverage) and concentration

Exploring the Data

Data Type and Presentation

The NSIDC Near-Real-Time Daily Polar Gridded Sea Ice Concentrations and the Daily and Monthly Polar Gridded Sea Ice Concentrations datasets are used to generate the monthly mean, trend, and anomaly images so that users of the product can monitor monthly mean ice conditions as they evolve.

Data are presented as images (in PNG format) that represent sea ice trends for the past 27 years. Monthly images are available that display sea ice concentration maps, and of anomalies in extent and concentration of sea ice.

Accessing the Data

To access data, users can go to the Compare Months and Years, Animate, or Download Data section of the Sea Ice Index. Users can examine single images or multiple images to generate maps showing sea ice extent, concentration, and anomalies.

For single images, users can choose either the Northern or Southern hemisphere to examine temporal parameters, including monthly and annual changes. The image displays an animation showing changes in sea ice extent relative to the median ice edge for a period spanning from 1978 to 2006 for the month chosen by the user.

Raw data can be accessed via FTP as PNG images and as text files that have monthly time series of Arctic and Antarctic ice extent.

Manipulating Data and Creating Visualizations

One way that users can process raw data is to import monthly concentration and extent numbers from text files into a spreadsheet application such as Excel. Graphs could be generated to visualize changes in sea ice extent over time. Users can also generate animations and visualizations using the tools on the Sea Ice Index Web site.

Tools for Data Manipulation

Raw data can be downloaded via FTP and imported into a spreadsheet application such as Excel for further processing. The Starting Point site provides a tutorial for using Excel.

About the Data

Collection Methods

Data are collected via satellites equipped with SSMR (Scanning Multichannel Microwave Radiometer) or SSM/I (Special Sensor Microwave Imager). These instruments measure the microwave radiation that is emitted by sea ice and sea water. Sea ice is distinguishable from water because it emits more microwave radiation than does water, and the microwave radiation emitted from water is more polarized than is that emitted from sea ice. Detailed explanations of the instrumentation used to collect data and the algorithms used to process data to obtain sea ice concentration and extent are available at the NSIDC. Detailed information on the SMMR and SSM/I instruments is available on the Physical Oceanography (more info) site of NASA's Jet Propulsion Laboratory.

Limitations and Sources of Error

Often, sea ice concentration is underestimated in the summer due to difficulties distinguishing melt water in ponds on the sea ice surface from open ocean water. This can lead to errorors in sea ice data for the summer months. More detailed explanations of sources of error can be found at the NSIDC.

References and Resources

Scientific References that Use this Dataset

Articles about the Sea Ice Index:
  • 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.

Education Resources that Use this Dataset

  • Study of Place, developed by TERC, has a module for middle-school students, which uses data to examine changes in sea ice extent.
  • Whither Arctic Sea Ice?, an Earth Exploration Toolbook chapter that provides teaching notes, a case study, and step-by-step instructions for using the sea ice index for examining how the extent of sea ice in the Arctic has diminished over time.
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Other Related Scientific References

Other related Education Resources

  • Experimenting with Ice Melt is part of a DLESE Teaching Box that allows students to simulate sea level changes due to changes in sea ice extent through experimentation.
  • Looking at Data: "Sea" Ice: A sea ice activity from the 'Using Data to Teach Earth Processes' Cutting Edge workshop.
  • A Sea level animation created by Paul Morin and Kent Kirkby (Department of Geology and Geophysics, University of Minnesota) allows users to explore the impact of rising sea levels relevant to current land masses.

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