Washington, DC, Oct 5 (BNO NEWS): The extent of sea ice covering the Arctic Ocean has declined to the second-lowest extent on record, NASA said on Tuesday.
The Arctic ice cap grows each winter as the sun sets for several months and shrinks each summer as the sun rises higher in the northern sky. Each year the Arctic sea ice reaches its annual minimum extent in September.
While it hit a record low in 2007, NASA and the NASA-supported National Snow and Ice Data Center (NSIDC) recorded the sea ice level last month at the University of Colorado in Boulder, showing that the summertime sea ice cover narrowly avoided a new record low.
Higher-than-average summer temperatures were also recorded last month, but without the unusual weather conditions that contributed to the extreme melt of 2007.
NSIDC scientist Walt Meier said the atmospheric and oceanic conditions were not as conducive to ice loss this year, but the melt still neared 2007 levels. "This probably reflects loss of multi-year ice in the Beaufort and Chukchi seas as well as other factors that are making the ice more vulnerable," Meier stated.
Meanwhile, Joey Comiso, senior scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said the continued low minimum sea ice levels fit into the large-scale decline pattern that scientists have watched unfold over the past three decades.
"The sea ice is not only declining, the pace of the decline is becoming more drastic," Comiso said. "The older, thicker ice is declining faster than the rest, making for a more vulnerable perennial ice cover."
The sea ice area as measured by the microwave radiometer on NASA's Aqua satellite dropped slightly lower than 2007 levels for about 10 days in early September, Comiso explained. However, the sea ice extent did not dip below the 2007 record.
Sea ice "area" differs from extent in that it equals the actual surface area covered by ice, while extent includes any area where ice covers at least 15 percent of the ocean.
On September 9, scientists captured the lowest point of arctic sea ice extent this year, which was 4.33 million square kilometers (1.67 million square miles). Averaged over the month of September, ice extent was 4.61 million square kilometers (1.78 million square miles).
This places 2011 as the second lowest ice extent both for the daily minimum extent and the monthly average. Ice extent was 2.43 million square kilometers (938,000 square miles) below the 1979 to 2000 average.
Over the last 30 years, a downward trend has been seen in the Arctic's low ice extent, which has continued until hist summer. Scientists have largely attributed this trend to warming temperatures caused by climate change.
Data show that Arctic sea ice has been declining both in extent and thickness. Since 1979, September Arctic sea ice extent has declined by 12 percent per decade.
NSIDC scientist Julienne Stroeve noted that the oldest and thickest ice in the Arctic continues to decline, especially in the Beaufort Sea and the Canada Basin. "This appears to be an important driver for the low sea ice conditions over the past few summers," Stroeve said.
Climate models, meanwhile, have suggested that the Arctic could lose almost all of its summer ice cover by 2100, but in recent years, ice extent has declined faster than the models predicted.