10 April 2012

THE FATE OF OLD SEA ICE

A few years ago sea ice covered a quarter of the Arctic Ocean. Now: 2 percent.
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Aerial view of the edge of the sea ice in Nunavut, Canada. Credit: Doc Searls via Wikimedia Commons .
  
The latest stats on 2012's sea ice in the Arctic are out from the National Snow and Ice Data Center (NSIDC). The winter of 2012 was not the lowest year since satellite monitoring began 34 years ago—but it was well below the average.
  
And the trend continues downward... as you can see in the graph below showing March sea ice extent since 1979.
  
Credit: National Snow and Ice Data Center.
  
Worse is the fate of old sea ice. 
  
Ice older than four years used to make up about a quarter of the wintertime sea ice cover in the Arctic. It now constitutes only 2 percent. From the NSIDC page:
  
Ice age data this year show that the ice cover remains much thinner than it was in the past, with a high proportion of first-year ice, which is thin and vulnerable to summer melt. After the record low minimum of 2007 the Arctic lost a significant amount of older, thicker ice, both from melting and from movement of ice out of the Arctic the following winter. In the last few years, the melt and export of old ice was less extreme than in 2007 and 2008, and multiyear ice started to re-grow, with second and third-year ice increasing over the last three years.
 
Arctic sea ice. Credit: Pink floyd88 a via Wikimedia Commons.
  
After the near-record summertime melt of 2011 there was a decline in two-year-old ice. And although some thicker three- and four-year-old ice managed to survive, the oldest, thickest ice—the stuff more than four years old—continued to decline. 
   
Credit: National Snow and Ice Data Center courtesy J. Maslanik and M. Tschudi, University of Colorado.
  
In the map above you can see how much of 2012's winter sea ice was new ice—just formed this year (purple). And how there's virtually nothing left of the old sea ice that was born five or more years ago (white).
  
Credit: National Snow and Ice Data Center courtesy J. Maslanik and M. Tschudi, University of Colorado.
  
The graph above shows the trend since 1983... how much old ice there used to be and what an endangered species it is now.
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