Tropical Cyclone Intensity Discrepancies

Song et al. (2010) write that "in recent years, there has been increasing interest in whether global warming is enhancing tropical cyclone (TC) activity," as has been claimed by Emanuel (2005) and Webster et al. (2005). One of the main sources of contention over this matter has been the fact that Wu et al. (2006) and Yeung (2006) examined the best track data from the Regional Specialized Meteorological Center (RSMC), Tokyo, Japan, as well as that of the Hong Kong Observatory of China (HKO); and "in contrast to Webster et al. (2005)," as Song et al. describe it, they found "there was no increase in category 4-5 typhoon activity in the western North Pacific [WNP] basin." In addition, they report that "neither RSMC nor HKO best track data suggest an increase in TC destructiveness." And they further state that "other studies also examined the differences in TC data sets from the Joint Typhoon Warning Center (JTWC) of the U.S. Naval Pacific Meteorology Oceanography Center in Hawaii, the RSMC, and the Shanghai Typhoon Institute (STI) of [the] China Meteorological Administration in Shanghai (Lei, 2001; Kamahori et al., 2006; Ott, 2006; Yu et al., 2007)," and they indicate that "so far, the reported trends in TC activity in the WNP basin have been detected mainly in the JTWC best track data set," which anomalous data set was employed by Emanuel (2005) and Webster et al. (2005) in drawing their anomalous conclusions.

To help resolve the discrepancies exhibited by the JTWC typhoon database, Song et al. analyzed differences of track, intensity, frequency and the associated long-term trends of those TCs that were simultaneously recorded and included within the best track data sets of the JTWC, the RSMC and the STI from 1945 to 2007.

In the words of the Chinese researchers, "though the differences in TC tracks among these data sets are negligibly small, the JTWC data set tends to classify TCs of category 2-3 as category 4-5, leading to an upward trend in the annual frequency of category 4-5 TCs and the annual accumulated power dissipation index, as reported by Webster et al. (2005) and Emanuel (2005)." And they add that "this trend and potential destructiveness over the period 1977-2007 are found only with the JTWC data set," while noting that actual downward trends "are apparent in the RSMC and STI data sets."

In light of the findings of Song et al., plus those of the other scientists they cite, there would appear to be little doubt that the studies of Emanuel (2005) and Webster et al. (2005) -- which climate alarmists long hailed as proof positive of their claim that global warming leads to more intense tropical cyclones/hurricanes -- actually provide no such evidence at all.

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

Kamahori, H., Yamazaki, N., Mannoji, N. and Takahashi, K. 2006. Variability in intense tropical cyclone days in the western North Pacific. SOLA 2: 104-107.

Lei, X. 2001. The precision analysis of the best positioning on WNP TC. Journal of Tropical Meteorology 17: 65-70.

Ott, S. 2006. Extreme Winds in the Western North Pacific. Rep. Rise-R-1544(EN), Riso National Laboratory, Technical University of Denmark, Copenhagen, 37 p.

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.

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.

Yeung, K.H. 2006. Issues related to global warming -- Myths, realities and warnings. Paper presented at the 5th Conference on Catastrophe in Asia, Hong Kong Observatory, Hong Kong, China, 20-21 June.

Yu, H., Hu, C. and Jiang, L. 2007. Comparison of three tropical cyclone intensity datasets. Acta Meteorologica Sinica 21: 121-128.