Introduction:
Arctic change

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Ice Extent:

The Arctic sea ice cover is a key indicator of climate chance. Ice extent is an important measure of the state of the ice cover. The extent of the sea ice cover is effectively monitored from satellite platforms using passive microwave imagery. The figure on the right shows monthly values of ice extent from 1978 to 2006.The largest signal is the seasonal cycle. Peak values typically occur in March and the minimum ice extent in September. The March - September seasonal variation is a little more than a factor of two.

Year to year trends can be examined by focusing on the ice extent in September as is discussed below.

 

Monthly values of Arctic sea ice extent.

The Arctic sea ice cover is in decline.  Observations show significant decreases in September sea ice extent.  Satellite-derived estimates of the minimum ice extent suggest a net reduction between 1978 and 1998 at a rate of 3% per decade. The rate of decline of the summer sea ice cover has been consistently accelerating in recent years and was 15% per decade from 1998 to 2008.  The 2007 summer sea ice extent marked a new record minimum for the period of passive microwave satellite observation beginning in 1979. At 4.3 million km2 the 2007 summer sea ice cover was 39 percent smaller than the long-term average from 1979 to 2000. An extended time series of sea ice extent, derived primarily from operational sea ice charts produced by national ice centers, suggests that the 2007 September ice extent was 50 percent lower than conditions in the 1950s to the 1970s [Stroeve et al., 2008].  Results from Stroeve et al. [2007] indicate that the observed decrease in Arctic summer sea ice extent is larger than that GCM ensemble mean prediction.


September ice extent anomaly

   

Decrease in September sea ice extent from 1980 to 2007 highlighted in red.
 

The maps above illustrate the tremendous decline in September ice extent from 1980 to 2007, with the ice losses highlighted in red. The ice extent decreased from 7.8 million square kilometers in 1980 to 4.3 million square kilometers in 2007. To put this loss into perspective consider that in September 1980 the extent of the Arctic sea ice cover was roughly comparable to the size of the continental United States. The area of ice lost by 2007 was equal to the entire United States east of the Missisippi plus the band of states from Minnesota down to Louisiana plus North Dakota plus part of South Dakota.

   
Ice Thickness:

While there is extensive 30 year long dataset for ice extent and concentration, much less is known about the thickness of the ice cover. A wide range of observations give indications that the ice cover is thinning. Satellite-based systems for monitoring ice thickness are currently under development. Submarine surveys of ice thickness provide the most data for time series analysis. The submarine ice thickness dataset is a set of snapshots in space and time complicating efforts to develop a climatological time series.  Results from Rothrock et al. (1999) shows changes in ice thickness comparing submarine results from the 1958 through 1976 to results from the 1990's. The results show that there was thinning at every point of comparison. The thinning averaged 40%, representing a decrease from about 3 m to less than 2 m (see figure below).

   
For more information check the State of the Cryosphere