Background
"During the past decade or so," in the words of Chan and Liu, "many researchers have suggested that the buildup of greenhouse gases (Watson et al., 2001) will likely result in a rise in sea surface temperature (SST), subsequently increasing both the number and maximum intensity of tropical cyclones (TCs)."  In their paper, therefore, they explore the validity of this assertion via an examination of pertinent real-world data because, as they put it, "if the frequency of TC occurrence were to increase with increasing global air temperature, one would expect to see an increase in the number of TCs during the past few decades," and especially, we might add, in light of the climate-alarmist claim that the warming of this period was unprecedented over the past one to two millennia.

What was done
A number of parameters related to SST and TC activity in the western North Pacific (WNP) were examined over the last four decades of the 20th century.

What was learned
The authors report that "these parameters have gone through large interannual as well as interdecadal variations," and that "they also show a slight decreasing [our italics] trend."  In addition, they say that "no significant correlation was found between the typhoon activity parameters and local SST," or "in other words," as they say to drive home their point, "an increase in local SST does not lead to a significant change of the number of intense TCs in the NWP, which is contrary to the results produced by many of the numerical climate models."  Instead, they find that "the interannual variation of annual typhoon activity is mainly constrained by the ENSO phenomenon through the alteration of the large-scale circulation induced by the ENSO event."

What it means
Chan and Liu write that the reason for the discrepancy between their real-world results and those of many of the numerical climate models likely lies in the fact that the models assume TCs are generated primarily from energy from the oceans and that a higher SST therefore would lead to more energy being transferred from the ocean to the atmosphere, or "in other words," as they again strive to make their point as clear as possible, they say that "the typhoon activity predicted in these models is almost solely determined by thermodynamic processes, as advocated by Emanuel (1999)," whereas "in the real atmosphere, dynamic factors, such as the vertical variation of the atmospheric flow (vertical wind shear) and the juxtaposition of various flow patterns that lead to different angular momentum transports, often outweigh the thermodynamic control in limiting the intensification process."  Their final conclusion, therefore, is that "at least for the western North Pacific, observational evidence does not support the notion that increased typhoon activity will occur with higher local SSTs."

References
Emanuel, K.A.  1999.  Thermodynamic control of hurricane intensity.  Nature 401: 665-669.

Watson, R.T.  and the Core Writing Team, Eds.  2001.  Climate Change 2001: Synthesis Report.  Cambridge University Press, Cambridge, UK.