Background
The authors note that "reports based on submarine sonar data [Rothrock et al., 1999; Wadhams and Davis, 2000] have suggested Arctic sea ice has thinned nearly by half in recent decades."  They further note that these reports were widely cited by both the Intergovernmental Panel on Climate Change (IPCC: Houghton et al., 2001) and by the popular media, who at the time of the reports' appearance were whipped into a frenzy over the subject by the climate alarmists' claim that humanity was responsible for the thinning because it was caused by global warming that was induced by anthropogenic CO2 emissions.

What was done
In a study designed to rationally evaluate these claims, the authors explored "how observations, theory, and modeling work together to clarify perceived changes to Arctic sea ice," incorporating data from "the atmosphere, rivers, and ocean along with dynamics expressed in an ocean-ice-snow model."

What was learned
Based on a number of different data-fed model runs, the authors report that for the last half of the past century, "no linear trend [in Arctic sea ice volume] over 50 years is appropriate," noting that their results indicate "increasing volume to the mid-1960s, decadal variability without significant trend from the mid-1960s to the mid-1980s, then a loss of volume from the mid-1980s to the mid-1990s."  The net effect of this behavior, in their words, was that "the volume estimated in 2000 is close to the volume estimated in 1950."

What it means
The authors' analysis suggests that the earlier inferred rapid thinning of Arctic sea ice was, as they put it, "unlikely," due to problems arising from "undersampling."  They also report that "varying winds that readily redistribute Arctic ice create a recurring pattern whereby ice shifts between the central Arctic and peripheral regions, especially in the Canadian sector," and that the "timing and tracks of the submarine surveys missed this dominant mode of variability."

References
Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Xiaosu, D., Maskell, K. and Johnson, C.A. (Eds.).  2001.  Climate Change 2001: The Scientific Basis.  Cambridge University Press, Cambridge, UK.

Rothrock, D.A., Yu, Y. and Maykut, G.A.  1999.  Thinning of the Arctic sea ice cover.  Geophysics Research Letters 26: 3469-3472.

Wadhams, P. and Davis, N.R.  2000.  Further evidence of ice thinning in the Arctic Ocean.  Geophysical Research Letters 27: 3973-3975.