The recent surge in tropical cyclone activity in the North Atlantic

Ocean has led to a flurry of papers concerning its cause, whether

anthropogenic global warming, natural variability, or a combination.

Holland and Webster (2007), has a good background and reference list on

this topic. In that particular study, the authors found that North

Atlantic Ocean tropical storm, hurricane, and major hurricane numbers

during the last century exhibited three stable and distinct regimes

separated by sharp transitions. Each regime has about 50% more tropical

storms and hurricanes annually than the previous one and is associated

with a distinct sea surface temperature (SST) range in the eastern

Atlantic Ocean, defined as the region 5-25oN, 55-20oW. Notwithstanding

the question of how accurate the data are, an issue well addressed by

Holland and Webster (2007), these conclusions are based upon an

incorrect interpretation of the data due to a lack of statistical

testing. Objective statistical tests, such as an f-test, a discriminant

analysis and cluster analysis cannot verify the existence of the climate

regimes proposed by Holland and Webster (2007) and are an artifact of

the way in which the data were plotted.

Holland, G. J., and P. J. Webster, 2007: Heightened tropical cyclone

activity in the North Atlantic: Natural variability or climate trend?

Phil. Trans. Roy. Soc. A, in press. (currently available at

http://www.pubs.royalsoc.ac.uk/media/philtrans_a/Holland%20and%20Webster%201.pdf)