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Super-Cyclone Frequency and Intensity "Down Under"
Reference
Nott, J. and Hayne, M. 2001. High frequency of 'super-cyclones' along the Great Barrier Reef over the past 5,000 years. Nature 413: 508-512.

What was done
One of the predicted consequences of CO2-induced global warming is an increase in the intensity and frequency of tropical cyclones. However, as the authors of this study note, determining if variations in what appear to be the intensity and frequency norms of such storms are a manifestation of anthropogenic effects "requires decoupling recent and future trends from longer-term periodicities."

In the present paper, the authors go a long way towards accomplishing this objective in one part of the world. Specifically, they produce a 5000-year record of tropical cyclone frequency and intensity along a 1500-km stretch of coastline in northeast Australia located between latitudes 13 and 24S by (1) geologically dating and tropographically surveying landform features left by historic hurricanes and (2) running numerical models to estimate storm surge and wave heights necessary to reach the landform locations.

What was learned
The authors' field and modeling work revealed that several "super-cyclones" with central pressures less than 920 hPa and wind speeds in excess of 182 kilometers per hour had occurred over the past 5000 years at intervals of roughly 200 to 300 years in all parts of the region of their study. They also report that the Great Barrier Reef "experienced at least five such storms over the past 200 years, with the area now occupied by Cairns experiencing two super-cyclones between 1800 and 1870." The 20th century, however, was totally devoid of such storms, "with only one such event (1899) since European settlement in the mid-nineteenth century."

What it means
Without the knowledge provided by this study, if a couple of super-cyclones were to strike the northeast coast of Australia sometime soon, climate-alarmists would likely attribute their occurrence to global warming. In fact, even with this knowledge, they would probably do so. It should be clear from the findings of this study, however, that such an occurrence would be nothing out of the ordinary, based on what we now know about the natural variability of such storms.


Reviewed 18 June 2003