Background
The authors write that "on the basis of hurricane thermodynamics it is plausible to expect hurricane strength to increase with increasing sea surface temperature," and they say that some recent papers have "claimed detection of such an increase (Emanuel, 2005; Webster et al., 2005; Holland and Webster, 2007) while others reported little or no trend (Solow and Moore, 2002; Landsea, 2005; Pielke, 2005; Klotzbach, 2006; Landsea et al., 2006; Nyberg et al., 2007; Kossin et al., 2007)."

What was done
To further explore this issue, Chylek and Lesins "apply simple statistical methods to the NOAA HURDAT record of storm activity in the North Atlantic basin between 1851 and 2007 to investigate a possible linear trend, periodicity and other features of interest."

What was learned
Using "a hurricane activity index that integrates over hurricane numbers, durations, and strengths," the two researchers report discovering "a quasi-periodic behavior with a period around 60 years superimposed upon a linearly increasing background." However, they note that "the linearly increasing background is significantly reduced or removed [our italics] when various corrections were applied for hurricane undercounting in the early portion of the record." Further noting that "the last minimum in hurricane activity occurred around 1980," Chylek and Lesins state that comparing the two 28-year-long periods on either side of this date, they find "a modest increase of minor hurricanes, no change in the number of major hurricanes, and a decrease in cases of rapid hurricane intensification." Hence, they conclude that "if there is an increase in hurricane activity connected to a greenhouse gas induced global warming, it is currently obscured by the 60-year quasi-periodic cycle."

What it means
In spite of the fact that the hurricane record analyzed by Cheylek and Lesins (1) started during the final stages of the Little Ice Age (which was the coldest period of the current interglacial), and that (2) the planet experienced a subsequent warming that has been declared by climate alarmists to have been unprecedented over the past millennium or more, there is still no convincing real-world evidence that global warming enhances either hurricane frequency or intensity.

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

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: 10.1098/rsta.2007.2083.

Klotzbach, P.J. 2006. Trends in global tropical cyclone activity over the past twenty years (1986-2005). Geophysical Research Letters 33: 10.1029/2006GL025881.

Kossin, J.P., Knapp, K.R., Vimont, D.J., Murnane, 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. 2005. Hurricanes and global warming. Nature 438: E11-E13.

Landsea, C.W., Harper, B.A., Hoarau, K. and Knaff, J.A. 2006. Can we detect trends in extreme tropical cyclones? Science 313: 252-254.

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.

Pielke, R.A. 2005. Are there trends in hurricane destruction? Nature 438: E11.

Solow, A.R. and Moore, L.J. 2002. Testing for trend in North Atlantic hurricane activity, 1900-98. Journal of Climate 15: 3111-3114.

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.