Background
Kwok introduces his new study by noting that near the mid-point of the last decade, simulations of Arctic Ocean sea ice characteristics produced by the climate models included in the World Climate Research Programme's Coupled Model Intercomparison Project phase 3 (CMIP3) were far from what it might have been hoped they would be. Specifically, he writes that (1) "Zhang and Walsh (2006) noted that even though the CMIP3 models capture the negative trend in sea ice area, the inter-model scatter is large," that (2) "Stroeve et al. (2007) show that few models exhibit negative trends that are comparable to observations," and that (3) "Eisenman et al. (2007) conclude that the results of current CMIP3 models cannot be relied upon for credible projections of sea ice behavior."

What was done
In his more recent analysis of the subject, based on the multi-model data set of Meehl et al. (2007), the Jet Propulsion Laboratory researcher compares CMIP3 model simulations "with observations of sea ice motion, export, extent, and thickness and analyzes fields of sea level pressure and geostrophic wind of the Arctic Ocean."

What was learned
Kwok's analysis demonstrates that "the skill of the CMIP3 models (as a group) in simulation of observed Arctic sea ice motion, Fram Strait export, extent, and thickness between 1979 and 2008 seems rather poor." He notes that "model-data differences and inter-model scatter of the sea ice parameters in the summarizing statistics are high," and that "the spatial pattern of Arctic sea ice thickness, a large-scale slowly varying climatic feature of the ice cover, is not reproduced in a majority of the models." Consequently, he writes that "the models will not get the main features of natural sea ice variability that may be dominating recent sea ice extent declines as well as the long-term greenhouse response [italics added]."

What it means
"Because the model simulations have difficulties reproducing the mean patterns of Arctic circulation and thickness," as Kwok writes in his concluding paragraph, " he says his analysis suggests there are "considerable uncertainties in the projected rates of sea ice decline even though the CMIP3 data set agrees that increased greenhouse gas concentrations will result in a reduction of Arctic sea ice area and volume." But with all the problems he finds with the models, who really knows how good those latter projections are?

References
Eisenman, I., Untersteiner, N. and Wettlaufer, J.S. 2007. On the reliability of simulated Arctic sea ice in global climate models. Geophysical Research Letters 34: 10.1029/2007GL029914.

Meehl, G.A., Covey, C., Delworth, T., Latif, M., McAvaney, B., Mitchell, J.F.B., Stouffer, R.J. and Taylor, K.E. 2007. The WCRP CMIP3 multi-model dataset: A new era in climate change research. Bulletin of the American Meteorological Society 88: 1383-1394.

Stroeve, J., Holland, M.M., Meier, W., Scambos, T. and Serreze, M. 2007. Arctic sea ice decline: Faster than forecast. Geophysical Research Letters 34: 10.1029/2007GL029703.

Zhang, X. and Walsh, J.E. 206. Toward a seasonally ice-covered Arctic Ocean: Scenarios from the IPCC AR4 model simulations. Journal of Climate 19: 1730-1747.