September 06, 2009
Sea Ice Down 53% Since 1980

US Navy submarine upward looking sonar profiles of the ice during the Cold War provides a longer term view into sea ice thickness changes.

While satellites provide accurate and expansive coverage of ice in the Arctic Ocean, the records are relatively new. Satellites have only monitored sea ice extent since 1973. NASA's Ice, Cloud, and land Elevation Satellite (ICESat) has been on the task since 2003, allowing researchers to estimate ice thickness as well.

To extend the record, Kwok and Drew Rothrock of the University of Washington, Seattle, recently combined the high spatial coverage from satellites with a longer record from Cold War submarines to piece together a history of ice thickness that spans close to 50 years.

Analysis of the new record shows that since a peak in 1980, sea ice thickness has declined 53 percent. "It's an astonishing number," Kwok said. The study, published online August 6 in Geophysical Research Letters, shows that the current thinning of Arctic sea ice has actually been going on for quite some time.

Average sea ice thickness declined from 3.64 to 1.89 meters. But if 1980 was a peak then what was the ice like in the 1960s and 1970s? Anyone seen the paper?

During the Cold War, the submarines collected upward-looking sonar profiles, for navigation and defense, and converted the information into an estimate of ice thickness. Scientists also gathered profiles during a five-year collaboration between the Navy and academic researchers called the Scientific Ice Expeditions, or "SCICEX," of which Rothrock was a participant. In total, declassified submarine data span nearly five decades—from 1958 to 2000—and cover a study area of more than 1 million square miles, or close to 40 percent of the Arctic Ocean.

Kwok and Rothrock compared the submarine data with the newer ICESat data from the same study area and spanning 2003 to 2007. The combined record shows that ice thickness in winter of 1980 averaged 3.64 meters. By the end of 2007, the average was 1.89 meters.

How good is the instrumentation of the Earth's climate at this point? How many more sensors would be needed to measure heat flows accurately enough to adjust for major influences and create better future projections?

Share |      Randall Parker, 2009 September 06 08:56 AM  Climate Trends

K said at September 6, 2009 2:32 PM:

Glad to see the information from the submarines is now available. I am not sure what the Soviets have released. French and British nuclear submarines probably weren't up there often, little data would come from them.

53% reduction does not sound astonishing. The Arctic sea area is mostly enclosed by land. Imagine filling a glass with crushed ice or cubes. As that melts. the surface remains covered by ice. Only when melting is far along do you see much water at the surface.

Of course the ice in your glass isn't being blown by wind or moved by currents. And it isn't being repeatedly refrozen by winter. So a little refinement is needed before you can publish in Science.

John Moore said at September 6, 2009 11:53 PM:

Interesting use of technology.

On the climate front, one should note that the loss of ice in the arctic is more than compensated by the gain of ice in the antarctic.

Charles Daubitz said at December 16, 2009 9:01 PM:

BS --- check ice yourself for any date

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