New record unlikely this year, NASA says
By Summit Voice
FRISCO — Arctic sea ice loss is unlikely to reach last year’s record low level, but there’s no sign of any recovery, either, NASA scientists said the week. This summer’s melt rate is consistent with the sustained decline of the Arctic ice cover observed by NASA and other satellites over the last several decades, the U.S. space agency said.
Overall, Arctic sea ice has declined at a rate of about 14 percent per decade since satellite measurements started in 1978, and rate has accelerated since 2007.
“Even if this year ends up being the sixth- or seventh-lowest extent, what matters is that the 10 lowest extents recorded have happened during the last 10 years,” said Walt Meier, a glaciologist with NASA’s Goddard Space Flight Center in Greenbelt, Md. “The long-term trend is strongly downward.”
The sea ice extent generally reaches its annual minimum in mid-September before starting to expand again. On Aug. 21, the extent was measured at 2.25 million square miles, compared to 1.67 million square miles last year at the same time. By mid-September in 2012, the ice dwindled down to just 1.32 million square miles, only half the average extent 1979 to 2010.
With only three weeks left in the melt season, the ice extent probably won’t fall below last year’s record, said Joey Comiso, senior scientist at Goddard and coordinating lead author of the Cryosphere Observations chapter of the upcoming report of the Intergovernmental Panel on Climate Change.
“But average temperatures in the Arctic fluctuate from one week to another, and the occurrence of a powerful storm in August, as happened in 2012, could cause the current rate of decline to change significantly,” Comiso said.
The Arctic sea ice cap has significantly thinned over the past decade and is now very vulnerable to melt, Comiso said. The multiyear ice cover, consisting of thicker sea ice that has survived at least two summers, has declined at an even faster rate than younger, thinner ice.
Meier said that a thinner, seasonal ice cover might behave more erratically in the summer than multiyear ice.
“First-year ice has a thickness that is borderline: It can melt or not depending on how warm the summer temperatures are, the prevailing winds, etcetera,” Meier said. “This year’s conditions weren’t super-favorable for losing ice throughout spring and summer; last year they were. Whereas with multiyear ice, it takes unusual warm conditions to melt it, which is what we’ve seen in the most recent years.”
On the opposite side of the planet, Antarctic sea ice, which is in the midst of its yearly growing cycle, is heading toward the largest extent on record, having reached 7.45 million square miles (19.3 million square kilometers) on Aug. 21. The rate at which the Arctic is losing sea ice surpasses the speed at which Antarctic sea ice is expanding.
The sea ice minimum extent analysis produced at Goddard – one of many satellite-based scientific analyses of sea ice cover – is compiled from passive microwave data from NASA’s Nimbus-7 satellite, which operated from late October 1978 to August 1987, and the U.S. Department of Defense’s Defense Meteorological Satellite Program, which has been used to extend the Nimbus 7 sea ice record onwards from August 1987. The record, which began in November 1978, shows an overall downward trend of 14.1 percent per decade in the size of the minimum summer extent, a decline that accelerated after 2007.