What was done
The authors analyzed the frequency and intensity of tropical cyclones that either originated in or entered the region of the central North Pacific (0-70°N, 140-180°W) over the 32-year period 1966-1997.

What was learned
In the words of the authors, "tropical cyclone activity (tropical depressions, tropical storms, and hurricanes combined) in the central North Pacific has been found to be on the rise and this amounts to [an increase of] about 3.2 cyclones over the last 32 years (1966-97)."  This increase, however, appears to be due to a step-change in the record such that there are "fewer cyclones during the first half of the record (1966-81) and more during the second half of the record (1982-1997)."  Accompanying the increase in tropical cyclone numbers is a similar increase in maximum hurricane intensity.

What it means
The authors say the observed increase in tropical cyclone activity cannot be due to global warming, because "global warming is a gradual processes" and "it cannot explain why there is a steplike change in the tropical cyclone incidences in the early 1980s."  Clearly, a much longer history of tropical cyclone activity in this part of the world will be needed to better understand the nature of the decadal-scale variations documented in this paper, as well as their relationship to mean global air temperature.