Andrew J. Dowdy
Tropical cyclone (TC) observations are used to examine changes in the TC climatology of the Australian region. The ability to investigate long-term changes in TC numbers improves when the El Niño-Southern Oscillation (ENSO) is considered. Removing variability in TC numbers associated with ENSO shows a significant decreasing trend in TC numbers at the 93–98% confidence level. Additionally, there is some indication of a temporal change in the relationship between ENSO and TC numbers, with ENSO accounting for about 35–50% of the variance in TC numbers during the first half of the study period, but only 10% during the second half.
ACE is not a very good metric of hurricane activity, since it does not consider storm size.
ReplyDeleteA better metric is TIKE:
http://davidappell.blogspot.com/2013/05/a-new-hurricane-metric.html
http://www.nature.com/nature/journal/v505/n7485/full/nature12882.html
ReplyDeleteGeoff
David Appell: TIKE, like ACE, both show a decline since the mid 1990s.
ReplyDeleteIf anything, TIKE shows a STEEPER decline than ACE.
The science actually predicted that global warming would make Australian tropical cyclones less common.
ReplyDelete5.9.1 Tropical cyclones
Similar to studies for other basins, Australian region studies indicate a likely increase in the proportion of the tropical cyclones in the more intense categories, but a possible decrease in the total number of cyclones.
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Since that time there has been a growing number of studies using results from medium and high resolution global climate models. The results from these studies indicate a consistent signal of fewer tropical cyclones globally in a warmer climate (Knutson et al 2006)
http://climatechangeinaustralia.gov.au/documents/resources/TR_Web_Ch5iv.pdf