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Australian-Region Tropical Cyclone Characteristics
Reference
Hassim, M.E.E. and Walsh, K.J.E. 2008. Tropical cyclone trends in the Australian region. Geochemistry, Geophysics, Geosystems 9: 10.1029/2007GC001804.

What was done
The authors analyzed tropical cyclone (TC) best track data pertaining to severe storms of the Australian region (5-30S) forming off Western Australia and the Northern Territory (the western sector: 90-135E, Indian Ocean) and off Queensland and the Gulf of Carpentaria (the eastern sector: 135-160E, Pacific Ocean) for the presence of systematic intensity and duration trends over the cyclone season periods running from 1969/1970 through 2004/2005.

What was learned
In the words of the two Australian researchers, "substantial differences in trends are found between the two sub-regions, with the number, average maximum intensity, and duration at the severe category intensities of tropical cyclones increasing since 1980 in the west but decreasing (in number) or exhibiting no trend (in intensity, severe category duration) in the east." And they add that it is not known "why the trends in the two adjacent Australian formation regions are so different."

What it means
Clearly, as Hassim and Walsh conclude, more study of Australian-region TCs will be required "to unravel the causes of the clear differences between cyclone trends in the eastern and western portions of the Australian basin." Until then, it will remain unclear what the overall data really suggest, and, of course, why. And even when these questions are answered, the temporal length of the underlying database will still be far too short to differentiate between a long-term trend that might possibly be tied to the warming that produced the Little Ice Age-to-Current Warm Period transition and a shorter-term cyclical regime shift. Hence, there is as yet no compelling support from the Australian region for the oft-stated climate-alarmist contention that global warming leads to more frequent and intense tropical cyclones.

Reviewed 29 October 2008