Meteorologists have known about the inter-decadal cycle and that we had entered a newly active phase of the cycle for a long time. This doesn't mean that it is the sole factor in increased activity, the same problem that applies with disattributing a single event to global warming applies to attributing it at least some partial factor; there's just no way to really discern. Certainly, there have been several highly anomalous things that are NOT normal and that have not been observed before. They could just be flukes, and our modern observation infrastrucutre certainly makes a difference in the quantity and quality of information.
The bottom line is just because a natural cycle predicts an increase, in the scheme of things, not much is really known about the details of that cycle (we've only observed a couple). In the same manner that one should be skeptical of any claims of global warming causation, one shouldn't automatically leap to the conclusion that all answers with increased activity lie in the multi-decadel signal either. Indeed, from the NOAA release (emphasis added):
There is consensus among NOAA hurricane researchers and forecasters that recent increases in hurricane activity are primarily the result of natural fluctuations in the tropical climate system known as the tropical multi-decadal signal.
Recent work finds a 30-year global increase in hurricane intensity strongly correlated with rising SSTs, although not conclusive such a strong signal on a global scale which effectively cancels out local cycles is quite interesting. Other factors are involved of course, but more ocean heat makes for more intense storms all things being equal, and the other factors involved require refining as does actual water temp influence. Also, the occurrence of "
Hurricane Catarina", only the second named storm ever observed in the south Atlantic (a TS formed off the African coast in the early 90s before the current active part of the cycle began), the first named storm ever observed in the western south Atlantic, and the first known hurricane ever in the enitre south Atlantic, in 2004 was unheardof; textbook meteorology says storms don't form in the southern Atlantic due to cooler temps and/or shear. but the occurrence of tropical cyclones there is predicted by some climate change models, and this occurred in an area that is expected to be drier in the current stage of the multi-decadel cycle (from NOAA release):
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The first South Atlantic hurricane: Unprecedented blocking, low shear and climate change" by Alexandre Bernardes Pezza and Ian Simmonds, Geophysical Research Letters (Vol 32, L15712, doi:10.1029/2005GL023390, 2005).
All this said, I agree that the current rise is (probably) primarily resultant of the tropical multi-decadal signal, and that the media has been irresponsible in
how it has presented the information and floated unsubstantied claims about global warming causing the rise in hurricanes and specifically Katrina.
Scott
Increasing destructiveness of tropical cyclones over the past 30 years by Kerry Emanuel, Nature (Vol 436, 4 August 2005, doi:10.1038/nature03906).
Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment by P. J. Webster et al, Science (16 September 2005, Vol 309, 10.1126/science.1116448).
Uncertainty in Hurricanes and Global Warming by Kevin Trenberth, Science (17 June 2005, Vol 308, 10.1126/science.1112551).
Hurricanes and Global Warming by R. A. Pielke Jr., et al (Bulletin of the American Meteorological Society, November 2005).
