With September right around the corner, the Arctic is nearing its annual sea-ice minimum, and while it may not be shaping up to be the lowest year on record, this year's rates place it squarely in line with the sustained decline observed by NASA and other satellites over the last several decades, according to the space agency.
"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."
According to NASA, the Arctic Ocean measured 2.25 million square miles on Aug. 21, compared to 1.67 million square miles in 2012, the smallest sea ice extent on record for this date, and 3.16 million square miles in 1996, the largest recorded for this date.
The smallest reach ever recorded, 1.32 million square miles, took place on Sept. 16, 2012, and represented roughly half of the average reach of Arctic sea ice between 1979 to 2010.
The first half of July saw a quick retreat of sea ice, but this was quickly slowed by low atmospheric pressures and clouds over the central Arctic that kept temperatures cooler than average. Now, with just three weeks of melting season to go, researchers doubt any records will be set, though, says 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, this can always change.
According to Comiso, "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."
The 2012 storm was especially effective due to the fact that it moved across an area of open water, mixing smaller pieces of ice with relatively warm water, thus causing rapid melting. This year's storms, meanwhile, have largely focused on areas of more consolidated ice, yielding fewer results.
However, Comiso notes, the Arctic sea ice cap is significantly thinner today than it was 10 years ago, leaving it more vulnerable to melting. The multiyear ice cover, which consists of thicker sea ice that has survived at least two summers, is currently melting at a rate faster than younger, thinner ice. And, as Meier explains, thinner, seasonal ice cover has the potential to behave more erratically during 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."