Background
"The 2005 hurricane season," in the words of the authors, "saw an unprecedented number of named tropical storms since records began in 1851." Moreover, they say it followed "on the heels of the unusual 2004 hurricane season when, in addition to the first South Atlantic hurricane, a record-breaking number of major hurricanes made landfall in the United States, also causing destruction on the Caribbean islands in their path." The question they thus posed for themselves is whether these things occurred in response to recent global warming or if they bore sufficient similarities with hurricane seasons of years past to preclude such an attribution.

What was done
Virmani and Weisberg compared various meteorological properties of the 2004 and 2005 hurricane seasons with those of prior seasons.

What was learned
The researchers report that "latent heat loss from the tropical Atlantic and Caribbean was less in late spring and early summer 2005 than preceding years due to anomalously weak trade winds associated with weaker sea level pressure," which "resulted in anomalously high sea surface temperatures" that "contributed to earlier and more intense hurricanes in 2005." However, they go on to note that "these conditions in the Atlantic and Caribbean during 2004 and 2005 were not unprecedented and were equally favorable during the active hurricane seasons of 1958, 1969, 1980, 1995 and 1998." In addition, they say "there is not a clear link between the Atlantic Multidecadal Oscillation [of temperature] or the long term trend [of temperature] and individual active hurricane years, confirming the importance of other factors in hurricane formation."

What it means
It would appear that the 2005 hurricane season was not as unique as many people have made it out to be, and that there is no compelling reason to ascribe whatever degree of uniqueness it may have possessed to recent global warming.