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2013 Ice Melt Will Not Be Record Year Despite Continuing Downhill Trends

August 23, 2013
Image Caption: Video still showing the size of the Arctic ice sheet as of August 15, 2013. Credit: NASA Goddard/JAXA

[WATCH VIDEO: Summer Arctic Ice Retreat 2013]

Lee Rannals for redOrbit.com – Your Universe Online

Arctic sea ice is reaching its annual “minimum” melt for the summer, but NASA says this year’s low will unlikely be breaking any records.

Last year, Arctic sea ice melted to a record low, making it the largest summer melt since satellites began measuring the process in 1979. This year’s melt is beginning to reach its minimum now, and even though it’s not going to catch any records, NASA said the melt-rate is still in line with the sustained decline of the Arctic ice seen over the past several decades.

“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 Arctic Ocean was measured at 2.25 million square miles on August 21; last year’s measurement at the same time was 1.67 million square miles. The largest recorded sea ice coverage for this date was in 1996 when the ice covered 3.16 million square miles.

The ice in the Arctic Ocean covers at least 15 percent of the ocean surface, making it an important target to observe as global warming trends continue to rise. This summer’s melting season included a fast retreat of the sea ice during the first half of July, but low atmospheric pressures and clouds helped keep temperatures cooler than average to slow down the plunge.

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 (IPCC), said that although three weeks of melting still remain, it is unlikely to reach any kind of record low.

“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 Ocean has witnessed a few summer storms, but none as intense as the cyclone that took place in August 2012.

“Last year’s storm went across an area of open water and mixed the smaller pieces of ice with the relatively warm water, so it melted very rapidly,” Meier said. “This year, the storms hit in an area of more consolidated ice. The storms this year were more typical summer storms; last year’s was the unusual one.”

Comiso said the Arctic sea ice cap has thinned over the past decades and is now very vulnerable to melt. The multiyear ice cover has declined at an ever faster rate than younger, thinner ice. This older coverage consists of a thicker sea ice that has survived at least two summers.

“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.”

NASA said Antarctic sea ice is also heading towards the largest extent on record, reaching 7.45 million square miles on measurements taken August 21. Although the ice coverage rate is climbing in the Antarctic, it is still not as fast as the rate ice is declining in the Arctic, NASA said.


Source: Lee Rannals for redOrbit.com - Your Universe Online



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