May 29, 2008

Tropical Cyclones Down-Under

Filed under: Climate Extremes, Hurricanes

We have written so much about the link between climate change and hurricanes (a.k.a., tropical cyclones, TCs) that we sometimes wonder if there could be anything new to report. No sooner than we have such a thought, yet another article on the subject appears in some leading scientific journal. A sentence in the abstract from this new article really caught our eye as we read “For the 1981/82 to 2005/06 TC seasons, there are no apparent trends in the total numbers and cyclone days of TCs, nor in numbers and cyclone days of severe TCs with minimum central pressure of 970 hPa or lower.”

This latest research gem appears in a recent issue of Geophysical Research Letters, and the work was conducted by a team of climatologists employed in Melbourne at the National Climate Centre of the Australian Bureau of Meteorology. Kuleshov et al. note that “Concern about the enhanced greenhouse effect affecting TC frequency and intensity has grown over recent decades. Recently, trends in global TC activity for the period 1970 to 2004 have been examined by Webster et al. [2005]. They concluded that no global trend has yet emerged in the total number of tropical storms and hurricanes.”

We at World Climate Report could not agree more, and the scientific evidence is overwhelming on the subject of global warming and hurricane frequency! Imagine the reaction we would get if we claimed “the science is settled” and the “debate is over” – hurricanes are not becoming more frequent! Yet, you can visit thousands of websites claiming that hurricanes are becoming more frequent thanks to the ongoing buildup of greenhouse gases. Climate change alarmists make this claim over and over, the claim is almost never challenged, and the claim is simply not consistent with reality. Give the global warmers credit – from school kids to grandmas, they have the world believing that hurricanes are definitely increasing in frequency, when nothing could be further from the truth.

The Australian-based Kuleshov et al. team wanted to focus on the Southern Hemisphere and they searched for data for an area from Africa to an oceanic area well off the coast of South America. The cold Peru ocean current off the west coast of South America inhibits (actually eliminates) hurricane activity in ocean area near South America. Kuleshov et al. state “The data for the Australian region (90°E to 160°E) has been provided by the Australian Bureau of Meteorology, for the area from 30°E to 90°E by Météo-France (La Réunion) and for the area east of 160°E by the Meteorological Services of Fiji and New Zealand.” They write “Further, TC trends in the SH as the whole domain as well as in two sub-regions, the South Indian Ocean (SIO) (west of 135°E) and the South Pacific Ocean (SPO) (east of 135°E), are derived.” The figure below (Figure 1)shows their study area along with a basic climatology of tropical cyclones in the Southern Hemisphere.


Figure 1. Average annual number of TCs in the Southern Hemisphere in El Niño years in 2° x 2° boxes.

Kuleshov et al. find “There are significant inter-annual variations in TC annual totals ranging from 16 to 34 TCs per year. Downward trends (statistically not significant) in the total annual number of TCs in the SH and in both sub-regions (SIO and SPO), have been identified.” We hate to bring this up to the global warming crusaders, but we did notice that the authors are writing about downward trends in the number of tropical cyclones of the Southern Hemisphere. The go on stating “There are no apparent trends in total annual occurrences of TCs in the SH for the 1981/82 to 2005/06 TC seasons, nor in severe TCs with minimum central pressure of 970 hPa or lower (i.e., the calculated trends are not statistically significant).” If you haven’t heard, they fire away in their summary again stating “For the 1981/82 to 2005/06 TC seasons, there are no apparent trends in the total numbers and cyclone days of TCs, nor in numbers and cyclone days of severe TCs with minimum central pressure of 970 hPa or lower.” To be complete, the authors do report that they detected an upward trend in the number of strong storms with a central pressure less than 945hPa.

Had these scientists found an increase in the total number of tropical cyclones in the Southern Hemisphere, they would need to hire press agents to handle the global coverage. Their work would be front page news all over the world, Time and Newsweek would be all over the story, and thousands of web pages would trumpet the results. However, they found no trends, or even downward trends, in total tropical cyclone frequency over a huge area of the planet – coverage at World Climate Report is about all they can expect.

References:

Kuleshov, Y., L. Qi, R. Fawcett, and D. Jones (2008), On tropical cyclone activity in the Southern Hemisphere: Trends and the ENSO connection, Geophysical Research Letters, 35, L14S08, doi:10.1029/2007GL032983.

Webster, P. J., G. J. Holland, J. A. Curry, and H.-R. Chang (2005), Changes in tropical cyclone number, duration, and intensity in a warming environment, Science, 309, 1844–1846.




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