Arctic sea ice volume up 50%

The volume of sea ice in the Arctic is 50 per cent higher than it was last fall, satellite measurements show.

In October 2013, the European Space Agency satellite CryoSat measured 9,000 cubic kilometres of sea ice on the Arctic Ocean, said an ESA news release Monday. At the same time of year in 2012, it measured just 6,000 cubic kilometres — a record low.

The satellite, launched in 2010, is designed to measure sea ice thickness across the Arctic Ocean, allowing scientists to monitor changes in volume and not just surface coverage.

Despite the short-term rebound, sea ice volumes remain low compared to historical averages, scientists say.

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“It’s estimated that there was around 20,000 cubic kilometres of Arctic sea ice each October in the early 1980s, and so today’s minimum still ranks among the lowest of the past 30 years,” said Andrew Shepherd, a co-author of the study, in a statement. Shepherd, who is a researcher at University College London, was part of a team that presented the study last week at the American Geophysical Union's annual meeting in San Francisco.

Both the surface coverage and volume of Arctic sea ice are monitored by scientists as climate indicators.

In September, the U.S. National Snow and Ice Data Centre reported that Arctic ice cover at its summer minimum this year was 5.1 million square kilometres. That was also up 50 per cent from last year's record low, but the sixth lowest on record. The seven lowest levels have all been recorded in the last seven years.

Coverage vs. volume

Scientists had noticed that generally, since CryoSat was launched in 2010, Arctic sea ice volumes haven't varied as much from year-to-year as sea ice coverage.

Because of that, they hadn't expected an increase in volume comparable to the increase in surface coverage, said Rachel Tilling, lead author of the new study, in a statement.

"But it has been, and the reason is related to the amount of multi-year ice in the Arctic,” added Tilling, a researcher at the U.K.'s Centre for Polar Observation and Modelling.

Multi-year ice survives more than one summer without melting and is considered an indicator of "healthy" Arctic sea ice cover, the ESA reported.

About 90 per cent of the increase in sea ice volume this year is from the growth of multi-year ice, which now averages about 20 per cent or 30 centimetres thicker than last year, the release said.

Last week, the NOAA issued its annual Arctic report card, which found that Arctic temperatures in 2013 were cooler compared to the past six years, although they remained warm compared to the 20th century.

"The Arctic caught a break, if you will, in 2013," said Martin Jefferies, the University of Alaska geophysicist who edited the report card, at the AGU conference. "But one year doesn't change the long-term trend toward a warmer Arctic."