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Western North Pacific Tropical Cyclone Trends
Wu, M.-C., Yeung, K.-H. and Chang, W.-L. 2006. Trends in western North Pacific tropical cyclone intensity. EOS, Transactions, American Geophysical Union 87: 537-538.

The authors set the stage for their study by noting that "using the tropical cyclone best track data from the U.S. Department of Defense's Joint Typhoon Warning Center (JTWC), Webster et al. (2005) found that between the two consecutive 15-year periods of 1975-1989 and 1990-2004, the percentage of typhoons in the western North Pacific meeting the definition of categories 4 and 5 on the Saffir-Simpson Hurricane Scale has increased from 25% to 41% of all typhoons in that ocean basin."

What was done
Wu et al. ran two independent checks on Webster et al.'s findings by performing similar analyses of best track data from the Regional Specialized Meteorological Centre (RSMC) Tokyo (Japan) and from the Hong Kong Observatory (HKO; Hong Kong, China).

What was learned
The three Chinese researchers report that "in contrast to Webster et al.'s findings, there was no increase in western North Pacific category 4-5 typhoon activity," and that "neither RSMC-Tokyo nor HKO best track data suggest an increase in western North Pacific tropical cyclone destructiveness as measured by the potential destructive index (PDI)," in contrast to the findings of Emanuel (2005). In fact, they say that the RSMC-Tokyo data "show a decrease in the proportion of category 4-5 typhoons from 18% to 8% between the two periods 1977-1989 and 1990-2004," that "the result is the same if the analysis is extended to include 2005," and that the trend is "statistically significant at the 5% level." In addition, they report that "HKO best rack data show a decrease in the proportion of category 4-5 typhoons, from 32% to 16%, between 1975-1989 and 1990-2004," that this result too is "statistically significant at the 5% level," and that it also "remains unchanged if the end year is extended to 2005."

What it means
Whereas the findings of Emanuel and Webster et al. have been unequivocally accepted by climate alarmists as factual, and highly hyped by them as having been driven by anthropogenic-induced global warming, Wu et al. say their contrary findings suggest that "the causes of discrepancies in these trends need to be better understood and the trends themselves need to be further ascertained," which developments we believe to be absolutely essential, in order to determine exactly what has occurred (or not occurred) in this regard, and why.

Emanuel, K.A. 2005. Increasing destructiveness of tropical cyclones over the past 30 years. Nature 436: 686-688.

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.

Reviewed 19 November 2008