6 October 2004

Arctic Sea Ice Continues To Disappear

by Kate Melville

Researchers from the University of Colorado have found that the extent of Arctic sea ice is continuing its rapid decline. Satellite information indicates the September 2004 sea ice extent was 13 percent below average, a reduction in area nearly twice the size of Texas. The decline in sea ice extent during September has averaged about 8 percent over the past decade. "This is the third year in a row with extreme ice losses, pointing to an acceleration of the downward trend," said Mark Serreze of CU-Boulder's National Snow and Ice Data Center (NSIDC).

"While a low September ice extent one year is often followed by a recovery the next year, this was not the case in 2003, which was about 12 percent below average," said Serreze. The September 2004 sea-ice loss was especially evident in extreme northern Alaska and eastern Siberia. "We're seeing more melting of multi-year ice in the summer," said Julienne Stroeve, a scientist with NSIDC. "We may soon reach a threshold beyond which the sea ice can no longer recover."

One possible explanation for the continuing loss of sea ice is that climate warming from human activities like the burning of fossil fuels is becoming more apparent. Climate models are in general agreement that one of the strongest signals of greenhouse warming will be a loss of Arctic sea ice. "Some indicate complete disappearance of the summer sea ice cover by 2070," said Serreze.

Serreze believes natural climate variability plays some part in the changes. "However, the most reasonable view is that the sea ice decline represents a combination of both natural variability and the greenhouse effect, with the latter becoming more evident in coming decades," he said.

A complicating factor is the atmospheric circulation pattern known as the Arctic Oscillation, which may be contributing to the loss of the much thicker "multi-year" ice that has accumulated over many years. "As winds and currents force this ice southward, more of it melts," said Stroeve. "And while new ice is still forming in the winters, it is thinner, and therefore melts faster in the summer than older ice."

Another CU-Boulder project involves the effects of climate change on North Slope communities in Alaska, including the effects of loss of ice cover on the potential for increased damage, erosion and flooding. Jim Maslanik of NSIDC said the retreat of the protective ice edge further offshore later into autumn has increased the potential for flooding and erosion for coastal communities such as Barrow.

"Another aspect of the changing ice conditions is that, in addition to the ice edge retreating far offshore, the rate of retreat of the ice edge has been very rapid," said Maslanik. "In recent years, this has resulted in unexpected impacts, such as unusually large numbers of polar bears being stranded on shore near Barrow."