What was done
In view of the fact that greenhouse warming is predicted to play a major role in polar regions, the authors analyzed century-long records of sea ice concentration and sea level pressure poleward of 40°N latitude to see what could be learned about this subject.

What was learned
A number of quasi-decadal and interdecadal timescale fluctuations were found to account for a large fraction (60-70%) of the natural climate variability in the Arctic.  Specifically, the authors identified climate signals with periods of 6-7 years, 9-10 years, 16-20 years, and 30-50 years; and they listed various oceanic processes that could be responsible for these variations.

What it means
Earth's climate is incredibly complex, varying simultaneously on a number of different timescales for a number of different reasons.  Against this backdrop of natural variability, it is extremely difficult to identify the anthropogenic greenhouse signal that has been predicted to result from the burning of fossil fuels.  As noted by Waleed Abdalati, as reported in the article "Earth's Fidgeting Climate" posted at Science@NASA on 20 October 2000, "you have all these processes mixed together that have been going on for thousands of years, and you're in the difficult position of trying to separate something very recent from the natural cycle without fully understanding what that natural cycle is."

Truly, the task is formidable; and it will yet be a very long time before we will ever - if ever! - be able to say with confidence that man has exerted a discernable influence on earth's climate, even in the Arctic where it is predicted to be especially noticeable.