The 1998 paper you quoted is a predictive model about typhoons in a global warming environment.

Quote Originally Posted by Royer et al. (1998).
Based upon alterations to the large scale atmospheric and oceanic conditions (vertical shear, vorticity and thermodynamic stability), they suggest that only small changes to the tropical cyclone frequencies may result: up to 10% increase in numbers in the Northern Hemisphere (primarily in the Northwest Pacific) and up to a 5% decrease in numbers in the Southern Hemisphere. These values should be considered very preliminary.
The MIT study is from the 31st July 2005 online Nature journal.

To explore that premise, Emanuel analyzed records of tropical cyclones--commonly called hurricanes or typhoons--since the middle of the 20th century. He found that the amount of energy released in these events in both the North Atlantic and the North Pacific oceans has increased markedly since the mid-1970s. Both the duration of the cyclones and the largest wind speeds they produce have increased by about 50 percent over the past 50 years.