Background
The authors write that "over the last four decades there has been a trend to earlier summer breakup of the sea ice in western Hudson Bay, Canada," and that "the trend to earlier sea-ice breakup has been linked to the long-term effect of warming in the region (Stirling et al., 1999; Gagnon and Gough, 2005)." Subsequently, however, they report that "the existence of a sufficiently long-term regional warming trend was disputed by Dyck et al. (2007)," and, therefore, they decided to explore the subject in a bit more detail, in order to see if they could resolve the controversy.

What was done
Working with passive microwave data obtained from the Scanning Multichannel Microwave Radiometer onboard the Nimbus 7 satellite, plus three Special Sensor Microwave/Imager instruments onboard Defense Meteorological Satellite Program satellites -- as well as Canadian Ice Service sea-ice charts that are considered to be "more accurate than passive microwave data for estimates of ice concentration, particularly in the presence of surface melt," as described by Agnew and Howell (2002) and Fetterer et al. (2008) -- Scot and Marshall performed several new analyses on both data sets, "bringing the time series up to date" (to 2007, from a starting date of 1971), while looking at "temperature trends in the area around the time of breakup in more detail than was [done] in previous studies."

What was learned
With respect to the chief point of controversy, the two researchers from the British Antarctic Survey found that "there has clearly not been a continuous trend in the [time of sea-ice breakup] data, and the change is best described by a step to 12 days earlier breakup occurring between 1988 and 1989, with no significant trend before or after this date [italics added]." In addition, they remark that "an increase in regional southwesterly winds during the first three weeks of June and a corresponding increase in surface temperature are shown to be likely contributing factors to this earlier breakup."

What it means
Proponents of CO2-induced global warming have long publicized what they have long believed to have been the gradual development, over the past four decades, of an earlier occurrence of the date of yearly sea-ice breakup in Canada's Hudson Bay, claiming that it was a manifestation of anthropogenic climate change that was negatively impacting the region's polar bears; but the newer findings of Scott and Marshall tend to argue against that conclusion. Nevertheless -- and correctly -- the two researchers conclude their analysis by stating that "it remains to be seen whether these changes in atmospheric circulation [which appear to be the proximate cause of the significant step-change in the date of sea-ice breakup] might be ascribed to human actions or simply to natural climate variability."

Clearly, the science pertaining to this matter is still not wholly settled; and, therefore, humanity cannot yet be blamed for what the world's climate alarmists consider to be the "bad behavior" of western Hudson Bay in regard to the temporal advancement of the yearly date of sea-ice breakup caused by the one-time adjustment in this parameter that occurred in the late 1980s.

References
Agnew, T.A. and Howell, S. 2002. Comparison of digitized Canadian ice charts and passive microwave sea-ice concentrations. Geoscience and Remote Sensing Symposium, IGARSS 2002 1: 231-233.

Dyck, M.G., Soon, W., Baydack, R.K., Legates, D.R., Baliunas, S., Ball, T.F. and Hancock, L.O. 2007. Polar bears of western Hudson Bay and climate change: Are warming spring air temperatures the "ultimate" survival control factor? Ecological Complexity 4: 73-84.

Fetterer, F., Knowles, K., Meier, W. and Savoie, M. 2008. Sea ice index. Boulder, Colorado: National Snow and Ice Data Center: http://nsidc.org/data/docs/noaa/g02135_seaice index/index.html.

Gagnon, A.S. and Gough, W.A. 2005. Trends in the dates of ice freeze-up and breakup over Hudson Bay, Canada. Arctic 58: 370-382.

Stirling, I., Lunn, N.J. and Iacozza, J. 1999. Long-term trends in the population ecology of polar bears in western Hudson Bay in relation to climatic change. Arctic 52: 294-306.