What was done
The authors used historical April through August ice observations made in the Nordic Seas - comprised of the Iceland, Greenland, Norwegian and Barents Seas, extending from 30°W to 70°E - to construct time series of ice-edge position anomalies spanning the period 1750-2002, which they analyzed for evidence of long-term trend and oscillatory behavior.

What was learned
Divine and Dick report that "evidence was found of oscillations in ice cover with periods of about 60 to 80 years and 20 to 30 years, superimposed on a continuous negative trend," which observations are indicative of a "persistent ice retreat since the second half of the 19th century" that began well before anthropogenic CO2 emissions could have had much of an effect on earth's climate.

What it means
Noting that the last cold period observed in the Arctic occurred at the end of the 1960s, the two Norwegian researchers say their results suggest that "the Arctic ice pack is now at the periodical apogee of the low-frequency variability," and that "this could explain the strong negative trend in ice extent during the last decades as a possible superposition of natural low frequency variability and greenhouse gas induced warming of the last decades." However, as they immediately caution, "a similar shrinkage of ice cover was observed in the 1920s-1930s, during the previous warm phase of the low frequency oscillation, when any anthropogenic influence is believed to have still been negligible." They suggest, therefore, "that during decades to come … the retreat of ice cover may change to an expansion." Hence, we should probably wait to see which view is proven to be correct before embarking on ambitious - not to mention futile and expensive - plans to alter the planet's climate before we know that it truly needs altering.