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Monthly sea ice climatologies now updated through 2007 in Atlas of the Cryosphere

Release Date: July 2, 2008

Monthly climatologies (monthly means) of sea ice extent and sea ice concentration in both hemispheres now include data that extend through 2007 in the Atlas of the Cryosphere. Previously, these climatologies averaged data for 1978 or 1979 through 2003, 2004, or 2005. They now consistently average the time period extending from 01 January 1979 through 31 December 2007.

Although these are still derived from spaceborne passive microwave remote sensing from the Scanning Multi-channel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) instruments, another important change is that the source data set for these layers has changed. Northern Hemisphere sea ice extent used to come from Northern Hemisphere EASE-Grid weekly snow cover and sea ice extent version 3 (Armstrong and Brodzik 2005) while Southern Hemisphere sea ice extent and concentration for both hemispheres were provided from Sea ice trends and climatologies from SMMR and SSM/I (Stroeve and Meier 1999). For consistency, the latter data set is now used for all of these layers. Furthermore, monthly mean sea ice concentration from Stroeve and Meier 1999 used to be a compilation of the Bootstrap sea ice concentrations from Nimbus-7 SMMR and DMSP SSM/I (Comiso 1999). As of June 2008, this data set is now instead a compilation of Sea ice concentrations from Nimbus-7 SMMR and DMSP SSM/I passive microwave data (Cavalieri et al. 1996) and has been updated through 2007. The switch from Comiso 1999 to Cavalieri et al. 1996 makes these monthly climatologies consistent with NSIDC's popular Sea Ice Index (Fetterer and Knowles 2002).

Lastly, Stroeve and Meier 1999 used to include concentrations ranging from 1-100%. With the recent update, these climatologies now exclude concentrations less than 15%. This concentration level is frequently used in the scientific community to define the sea ice edge. A threshold of 15% is also used to define the extent of sea ice in the sea ice extent layers.

Updated monthly climatologies (1979-2007) of sea ice extent (left column) and concentration (right column) for January (top row) and September (bottom row). Click each image to view an animation of all 12 months.

We welcome your feedback on this project. If you have questions, comments or suggestions, please contact NSIDC User Services at +1.303.492.6199,, or via our online contact form. The development of this map server application was supported by NASA's Earth Observing System (EOS) Program under contract NAS5-03099 and was developed using MapServer, an Open Source development environment for building spatially-enabled internet applications. The Atlas of the Cryosphere was developed by John Maurer. Future updates will continue to be announced on this RSS feed.