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On Deriving a History of Atlantic Tropical Cyclone Numbers
Landsea, C.W. 2007. Counting Atlantic tropical cyclones back to 1900. EOS, Transactions, American Geophysical Union 88: 197, 202.

Landsea reports that Mann and Emanuel (2006) used quantitative records stretching back to the mid-nineteenth century to develop "a positive correlation between sea surface temperatures and Atlantic basin tropical cyclone frequency for the period 1871-2005," and that Holland and Webster (2007) analyzed Atlantic tropical cyclone frequency back to 1855 and found "a doubling of the number of tropical cyclones over the past 100 years," noting that "both papers linked these changes directly to anthropogenic greenhouse warming."

What was done
Because of the great controversy surrounding the subject, and as a result of his extreme familiarity with it, the author illustrates a number of possible biases that may exist in the cyclone frequency trends derived in the two studies mentioned above, which are used by climate alarmists to promote their claim that anthropogenic CO2 emissions have caused Atlantic tropical cyclones to become increasingly more numerous with the passage of time.

What was learned
In light of the many compelling and data-based arguments that he presents, Landsea concludes that "improved monitoring in recent years is responsible for most, if not all, of the observed trend in increasing frequency of tropical cyclones." We agree with both his analyses and his conclusions; and we note that other much longer reconstructions of hurricane frequency based on various types of proxy data (Donnelly and Woodruff, 2007; Nyberg et al., 2007; Nott et al., 2007) also support the implication that anthropogenic greenhouse warming has not been responsible for any increase in the frequency of occurrence of intense hurricanes.

What it means
With each passing week, almost, the evidence against anthropogenic-induced increases in the frequency and intensity of tropical cyclones and hurricanes continues to mount. So why do people like Al Gore continue to chant just the opposite? Enquiring minds want to know.

Donnelly, J.P. and Woodruff, J.D. 2007. Intense hurricane activity over the past 5,000 years controlled by El Niņo and the West African Monsoon. Nature 447: 465-468.

Holland, G.J. and Webster, P.J. 2007. Heightened tropical cyclone activity in the North Atlantic: Natural variability or climate trend? Philosophical Transactions of the Royal Society of London, Series A: in press.

Mann, M. and Emanuel, K. 2006. Atlantic hurricane trends linked to climate change. EOS, Transactions, American Geophysical Union 87: 233, 238, 241.

Nott, J., Haig, J., Neil, H. and Gillieson, D. 2007. Greater frequency variability of landfalling tropical cyclones at centennial compared to seasonal and decadal scales. Earth and Planetary Science Letters 255: 367-372.

Nyberg, J., Malmgren, B.A., Winter, A., Jury, M.R., Kilbourne, K.H. and Quinn, T.M. 2007. Low Atlantic hurricane activity in the 1970s and 1980s compared to the past 270 years. Nature 447: 698-701.

Reviewed 25 July 2007