Background
The authors write that "in the current debate on global warming and the change in the number of intense cyclones, initial studies carried out have shown very different results for the northern Indian Ocean," where, as they describe it, "Webster et al. (2005) found that there had been a considerable increase in the number of categories 4 and 5 cyclones with a maximum sustained wind reaching at least 115 knots." However, they say that Landsea et al. (2006) subsequently demonstrated that the databases employed by Webster et al. "were not sufficiently reliable," as "cyclones archived as being categories 2 or 3 had been re-analyzed and assigned as categories 4 or 5." And they additionally state that a year later, "Kossin et al. (2007) did not note any trend towards an increase in the number of categories 4 and 5 cyclones in the northern Indian Ocean for their period of analysis, which covered from 1983 to 2005."

What was done
To provide what they describe as "other considerations," Hoarau et al. analyzed intense cyclone activity in the northern Indian Ocean from 1980 to 2009 on the basis of a homogenous re-analysis of satellite imagery.

What was learned
Not mincing any words, the three French researchers simply report that "there has been no trend towards an increase in the number of categories 3-5 cyclones over the last 30 years," noting that "the decade from 1990 to 1999 was by far the most active with 11 intense cyclones while 5 intense cyclones formed in each of the other two decades," i.e., those that preceded and followed the 1990s. And they add that there has also "not been a regular increase in the number of cyclone 'landfalls' over the last three decades (1980-2009)."

What it means
Once again, we have another real-world example of the occurrence of intense tropical cyclone activity being totally independent of concomitant mean global air temperature over the past three decades.

References
Kossin, J.P., Knapp, K.R., Vimont, D.J., Murname, R.J. and Harper, B.A. 2007. A globally consistent reanalysis of hurricane variability and trends. Geophysical Research Letters 34: 10.1029/2006GL028836.

Landsea, C.W., Harper, B.C., Hoarau, K. and Knaff, J.A. 2006. Can we detect trends in extreme tropical cyclones? Science 313: 452-454.

Webster, P.J., Holland, G.J., Curry, J.A. and Chang, H.R. 2005. Changes in tropical cyclone number, duration, and intensity in a warming environment. Science 309: 1844-1846.