Background
The author writes that "debates have occurred about whether there are sufficient data to ascertain any true departures in the behavior of tropical cyclones [TCs] from their natural variability," and he notes that "Quaternary data have not figured prominently in recent debates concerning TC natural variability versus potential anthropogenic global warming-induced changes; nor have the Quaternary data been used to any substantial degree in numerical model projections concerning the future behavior of TCs."

What was done
In an attempt to fill this void, Nott provides a brief review of the subject, noting that there are "at least 15 different methods for reconstructing long-term records of TCs."

What was learned
With respect to the status of the current debate, the Australian researcher reports that "recent analyses of corrected historical TC records suggest that there are no definitive trends towards an increase in the frequency of high-intensity TCs for the Atlantic Ocean region (Knutson et al., 2010), the northwest Pacific (Chan, 2006; Kossin et al., 2007) and the Australian region, South Pacific and south Indian oceans (Kuleshov et al., 2010)." He notes, however, that "over multi-century to millennial timescales, substantial change has occurred in virtually all TC-generating regions of the globe," with "alternating periods of lesser and greater activity," writing that "the longer, coarser-resolution records display periods from multi-century to over a millennium in length, whereas the higher-resolution records register multi-decadal to centennial-length periodicities." In some of these cases, Nott says that (1) "different climate states, such as periods dominated by El Niņos and La Niņas, appear to be responsible for the TC variability." In other cases, he says the responsible factor seems to be (2) shifts in the position of the jet stream, (3) solar variability, or (4) some unknown cause.

What it means
In concluding his review, Nott writes "there is still considerably more data needed before causes of the long-term variability of TCs can be comprehensively identified," and he says that "a better understanding of this long-term variability will be critical to understanding the likely future behavior of TCs globally and especially so when attempting to detect and attribute those future changes." Thus, one ought not get too excited about climate-alarmist claims that global warming leads to increases in either the frequency or intensity of tropical cyclones and hurricanes, as there is as yet no comprehensive set of real-world data that point in that direction.

References
Chan, J.C.L. 2006. Comment on "Changes in tropical cyclone number, duration, and intensity in a warming environment." Science 311: 1713.

Knutson, T.R., McBride, J.L., Chan, J., Emanuel, K., Holland, G., Landsea, C., Held, I., Kossin, J.P., Srivastava, A.K. and Sugi, M. 2010. Tropical cyclones and climate change. Nature Geoscience 3: 157-163.

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.

Kuleshov, Y., Fawcett, R., Qi, L., Trewin, B., Jones, D., McBride, J. and Ramsay, H. 2010. Trends in tropical cyclones in the South Indian Ocean and the South Pacific Ocean. Journal of Geophysical Research 115: 10.1029/2009JD012372.