What was done
The authors extended prior satellite-derived Arctic and Antarctic sea ice records several years back in time by bridging the gap between Nimbus 7 and earlier Nimbus 5 satellite data sets via comparisons with National Ice Center digital sea ice data.

What was learned
For the newly-extended period of 1972-2002, Arctic sea ice extent declined at a mean rate of 0.30 ± 0.03 x 10⁶ km² per decade; while for the more recent period from 1979-2002, it declined at a mean rate of 0.36 ± 0.05 x 10⁶ km² per decade, or at a rate that was 20% greater than the full-period rate.  In the Antarctic, on the other hand, for the newly-extended period of 1973-2002, sea ice extent declined at only half the mean rate at which it declined in the Arctic, i.e., at 0.15 ± 0.08 x 10⁶ km² per decade; while for the more recent period from 1977-2002, it actually increased at a mean rate of 0.10 ± 0.05 x 10⁶ km² per decade.

What it means
The Arctic results are compatible with the spin that is typically put on them by climate alarmists; that is, they indicate a greater rate of sea ice melting during the latter part of the 20th century, when global warming is claimed to have occurred at an unprecedented rate.  The story from the Antarctic, however, is at odds with this interpretation, with sea ice extent actually changing from its prior negative trend to a positive trend over the period of supposedly unprecedented temperature increase.  One might think, therefore, that real-world data lead to a draw over the dispute about earth's recent temperature history.  If it is truly global warming that is being debated, however, one would - at the very least - not expect Southern Hemispheric sea ice to be increasing in extent over the past quarter-century.  Hence, we still say that the balance of real-world evidence testifies against the climate-alarmist notion that the world is experiencing unprecedented global warming.