Illustration courtesy National Snow and Ice Data Center
The giant ice cube bobbing on the top of the planet just got smaller.
Warming sea and air probably caused the Arctic sea ice to melt to its lowest volume on record this summer, the University of Colorado at Boulder’s National Snow and Ice Data Center reported today.
Certainly, 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 Sept. 14, the researchers said.
“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,” the scientists explained.
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 million square miles in 2005.
The 2008 low strongly reinforces the 30-year downward trend in Arctic sea ice extent, said 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, he said.
“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.”
Temperatures in 2008 were cooler than in 2007, although still warmer than average. Cloudier skies also protected the ice from some melt, and wind patterns spread the ice pack out, leading to higher extent numbers, according to Julienne Stroeve, an NSIDC research scientist. The end result was the natural variability of short-term weather patterns provided enough of a “brake” to prevent a new record-low ice extent from occurring, she said.
“I find it incredible that we came so close to beating the 2007 record, without the especially warm and clear conditions we saw last summer,” Stroeve said . “I hate to think what 2008 might have looked like if the weather patterns had set up in a more extreme way.”
The melt season of 2008 reinforces the decline of Arctic sea ice documented over the past 30 years, said Ted Scambos, NSIDC lead scientist. “The trend of decline in the Arctic continues, despite this year’s slightly greater extent of sea ice,” Scambos said. “The Arctic is more vulnerable than ever.”