The Australian Bureau of Meteorology's J Callaghan and S.B. Power's new paper is titled; "Variability and decline in the number of severe tropical cyclones making land-fall over eastern Australia since the late nineteenth century."
Callaghan and Power write that the Intergovernmental Panel on Climate Change, or IPCC, highlights several studies that conclude that "tropical cyclones are likely to become more intense in the future in response to global warming," citing Alley et al. (2007); but rather than accepting this set of claims on the basis of the IPCC's "authority," they go on to provide a much more compelling analysis of their own.
What was learned
The two researchers with Australia's Bureau of Meteorology first note that their new data base allows them "to document changes over much longer periods than has been done previously for the Southern Hemisphere," and among the host of results they describe, two of them stand out with respect to their significance to the global warming debate. First, they report that "the sign and magnitude of trends calculated over 30 years periods vary substantially," highlighting the fact that "caution needs to be taken in making inferences based on e.g. satellite era data only." And second, they report that "the linear trend in the number of severe TCs making land-fall over eastern Australia declined from about 0.45 TC/year in the early 1870s to about 0.17 TC/year in recent times -- a 62% decline." And they add that "this decline can be partially explained by a weakening of the Walker Circulation, and a natural shift towards a more El Niño-dominated era." Thus, they conclude the abstract of their paper with the remark that "the extent to which global warming might also be partially responsible for the decline in land-falls -- if it is at all -- is unknown [bold and italics added to highlight the irony of the result]."
What it means
Callaghan and Power's analysis of their lengthy and comprehensive new data base reveals results that appear to be totally at odds with the contentions of the IPCC, which are based more on the output of numerical models of the atmosphere than on real-world observations. And their results also highlight the fact that even real-world observations may be misleading, especially if they do not cover a long enough time period to reveal the oscillatory nature of various aspects of earth's climate.