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Summer 2015 tally of Arctic Ocean ice volume confirms long-term decline

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Posted September 23, 2015

A University of Washington tool that monitors the amount of ice in Arctic waters calculated that we remain on track for a gradual disappearance of the Arctic ice cap in summer.

“Last year, when the ice had bounced back by some percentage both in extent and in volume, there was a bit of talk about whether that constituted a recovery,” said Axel Schweiger, a sea ice scientist with the UW Applied Physics Laboratory. “I think it’s significant that we’re back on the downward trend.”

Arctic sea ice extent for September 11, 2015, was 4.41 million square kilometers (1.70 million square miles). The orange line shows the 1981 to 2010 average extent for the day. The black cross indicates the geographic North Pole. Image credit: National Snow and Ice Data Center

Arctic sea ice extent for September 11, 2015, was 4.41 million square kilometers (1.70 million square miles). The orange line shows the 1981 to 2010 average extent for the day. The black cross indicates the geographic North Pole. Image credit: National Snow and Ice Data Center

On Sept. 15, the U.S. National Snow & Ice Data Center announced the 2015 minimum aerial extent for sea ice. Its value, based mainly on satellite images, calculates how much of the ocean’s surface is covered in ice at the annual minimum, which this year occurred on Sept. 11. The 2015 value, the agency said, is the fourth-lowest on record since observations began in 1978.

A widely used UW calculation of ice volume shows this year’s sea ice volume minimum — a different measurement than the aerial extent for sea ice — was reached a day later, on Sept. 12. The UW-developed tool incorporates satellite measurements with of ice extent and ocean temperatures into a computer model of sea ice to calculate the amount of ice floating in Arctic waters. The total volume on Sept. 12 was 1,360 cubic miles, the group announced Sept. 17.

“From an energy point of view, volume basically tells the story of how much ice has melted, or how much ice has grown back,” Schweiger said. “Some years may have less ice extent, but it maybe be thicker.”

The sea ice volume peaks in April and reaches a minimum in September. This year’s value, the red line, is the fourth lowest on record. Image credit: UW Applied Physics Laboratory

The sea ice volume peaks in April and reaches a minimum in September. This year’s value, the red line, is the fourth lowest on record. Image credit: UW Applied Physics Laboratory

The ice volume measurements follow the trend seen in the ice extent. The 2015 volume is about 290 cubic miles below last year’s value, when there was a substantial rebound in Arctic sea ice. This year is just 72 cubic miles above the value for 2013, and continues the long-term declining trend with shorter-term wiggles up and down — including the exceptionally low ice in 2012, and the relatively greater ice last summer.

“The long-term outlook is for this sea ice to further decrease,” Schweiger said. “There will be short periods of ups and downs, the expectation over the next few decades is for continued ice loss.”

The UW-developed Pan-Arctic Ice Ocean Modeling and Assimilation System, or PIOMAS, usually produces monthly data releases. The group compares sea ice volume against calculations going back to 1979, when Arctic summer sea ice volume was several times the current values. The group did a special mid-month update to coincide with this year’s sea ice minimum.

Source: University of Washington

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