There is plenty of talk about Arctic sea ice extent, but what is happening to the volume?
Sea ice volume takes into account both sea ice thickness and extent, which makes it the most important factor in measuring the overall health of sea ice.
Arctic Sea Ice Volume is an important indicator of climate change because it accounts for variations in sea ice thickness as well as sea ice extent. Total Arctic sea ice volume cannot currently be observed continuously. Observations from satellites, Navy submarines, moorings, and field measurements are limited in space or time. The assimilation of observations into numerical models, currently provides one way of estimating sea ice volume changes on a continuing basis. (from the UW's PolarScience Center.)
As you can see by the University of Washington PIOMAS graph below, Arctic sea ice volume has been on a steady decline since the late 1970s. Now it is about 70% lower than the mean.
The bottom image below shows the changes in Arctic sea ice since 1981. You can see that thinner, less than 1 year old ice has increased, while thicker, multi-year ice has decreased. Image courtesy of the NSIDC.
Not convinced? Let's hear from the experts......
Some of you may still think that the Arctic sea ice is recovering. You state that in 2008, Arctic sea ice reached a minimum extent that was about 10 percent greater than the record low of 2007, and the minimum extent in 2009 was greater than either 2007 or 2008.
The data suggest that the ice reached a record low volume in 2008, and has thinned even more in 2009. Sea ice extent normally varies from year to year, much like the weather changes from day to day. But just as one warm day in October does not negate a cooling trend toward winter, a slight annual gain in sea ice extent over a record low does not negate the long-term decline, according to the NSIDC. So, what would scientists call a recovery in sea ice? First, a true recovery would continue over a longer time period than two years. Second, scientists would expect to see a series of minimum sea ice extents that not only exceed the previous year, but also return to within the range of natural variation. In a recovery, scientists would also expect to see a return to an Arctic sea ice cover dominated by thicker, multi-year ice, according to the NSIDC FAQ section.
The image below shows the changes in ice thickness between March 1988 and 2010. Image courtesy of the NSIDC. Note how much the thicker, multi-year ice has decreased. First-year ice is usually much thinner and more susceptible to complete melting during the summer months.
In November of 2010, Rear Admiral Titley, a U.S. Navy oceanographer testified that there will be 4 weeks of ice free conditions in the Arctic during the summer months by the mid to late 2030's.
To sum up, I personally find no evidence that Arctic sea ice is recovering in terms of both extent and thickness.
Many thanks to the National Snow and Ice Data Center and the University of Washington for their excellent graphics and data.
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