Arctic Sea Ice in 2007: A Year to Remember

Typically, the absolute minimum Arctic sea ice cover occurs during the second week in September. However in 2007, Arctic sea ice extent surpassed all previous records for the lowest absolute minimum over the satellite era (1979 to present) by the middle of August. Averaged over the entire month, Arctic sea ice extent for August 2007 was only 5.32 million sq-km, falling well below the long-term mean (1979-2000) of 7.67 million sq-km. Even more noteworthy was that the August 2007 monthly average was lower than the previous record minimum set in September 2005 of 5.56 million sq-km and there was still a month of melt left. At the end of the melt season, the ice cover during September 2007 dropped an additional 23% compared to September 2005, ending up with a final monthly mean value of 4.28 million sq-km. Extending the modern satellite record back in time with data from the Hadley Centre sea ice and sea surface temperature data set (HadlSST), shows that September 2007 represented a 50% reduction compared to conditions in the 1950s - 1970s.

While the causes of the rapid and extreme sea ice losses this summer remain to be fully understood, it appears that key factors included superposition of an unusual pattern of atmospheric circulation upon an overall thinning of the pack ice in recent decades. This talk addresses the key factors contributing to the rapid and extreme ice loss in summer 2007 and discusses the future of the Arctic sea ice cover through analysis of climate model simulations and observations.