Washington, Oct 3 : Arctic sea ice extent during the 2008 melt season dropped to the second-lowest level since satellite measurements began in 1979, reaching the lowest point in its annual cycle of melt and growth on September 14.
Preliminary data also indicate 2008 may represent the lowest volume of Arctic sea ice on record.
The declining Arctic sea ice is due to rising concentrations of greenhouse gases that have elevated temperatures across the Arctic and strong natural variability in Arctic sea ice.
Average sea ice extent during September, a benchmark measurement in the scientific study of Arctic sea ice, was 1.8 million square miles.
The record monthly low, set in 2007, was 1.65 million square miles. The third lowest monthly low was 2.15 square miles in 2005, according researchers at the center.
The 2008 low strongly reinforces the 30-year downward trend in Arctic sea ice extent, according to CU-Boulder Research Professor Mark Serreze, an NSIDC senior scientist.
The 2008 September low was 34 percent below the long-term average from 1979 to 2000 and only 9 percent greater than the 2007 record.
Because the 2008 low was so far below the September average, the negative trend in the September extent has been pulled downward, from a minus 10.7 percent per decade to a minus 11.7 percent per decade.
"When you look at the sharp decline we have seen over the past 30 years, a recovery from lowest to second lowest is no recovery at all," Serreze said. "Both within and beyond the Arctic, the implications of the decline are enormous," he added.
According to the researchers, conditions in the spring, at the end of the growth season, played an important role in the outcome of this year's melt.
In March 2008, thin first-year ice covered a record high 73 percent of the Arctic basin.
While it may appear to be a recovery of the sea ice, the large extent masked an important aspect of sea ice health since thin ice is more prone to melting during the summer.
Through the 2008 melt season, a race developed between the melting of thin ice and gradually waning sunlight.
Summer ice losses allowed significant solar energy to enter the ocean and heat up the water, melting even more ice from the bottom and sides.
"Warm ocean waters helped contribute to ice losses this year, pushing the already thin ice pack over the edge," said CU-Boulder Research Associate Walt Meier.
"In fact, preliminary data indicate that 2008 probably represents the lowest volume of Arctic sea ice on record, partly because less multiyear ice is surviving now and the remaining ice is so thin," he added.