Prompted by the proofs of my review of AIT for Met Apps (oh, the fame!) I looked at the site again and found The Science. What they list there is very thin and with no useful links. I would have hoped for something better.
Anyway, their first point is "The number of Category 4 and 5 hurricanes has almost doubled in the last 30 years." and they source this to Emanuel, K. 2005. Increasing destructiveness of tropical cyclones over the past 30 years. Nature 436: 686-688. Now E does say This combined PDI has nearly doubled over the past 30 yr, but never uses the word "category". And this is not surprising, because it starts Theory and modelling predict that hurricane intensity should increase with increasing global mean temperatures, but work on the detection of trends in hurricane activity has focused mostly on their frequency and shows no trend. The paper is about the destructiveness index, not the number of storms. Has Gore... simply misinterpreted the paper? Found something in it my quick skim missed? Or wot?
So... anyone know a good source for hurricane numbers, and how they have changed?
[Update: OK... I think I have to largely forgive them this. Their reference is wrong (it should be Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment, P. J. Webster, G. J. Holland, J. A. Curry, H.-R. Chang but it does say: "hurricanes in the strongest categories (4 + 5) have almost doubled in number (50 per pentad in the 1970s to near 90 per pentad during the past decade) and in proportion (from around 20% to around 35% during the same period). These changes occur in all of the ocean basins". Thanks to SB for pointing this out -W]
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Somebody's confused "number" and "percent" perhaps?
I tried searching on the tiny scrap of science info you found somewhere deep in there
(thank you, I'd never have found that --- haven't those people heard of the Americans with Disabilities Act requirement for accessible text? almost the whole dadratted website appears to be flash animation, it's defeated me completely in past tries.)
The search led me to text:
http://www.ucsusa.org/global_warming/science/hurricanes-and-climate-cha…
and this illustration here:
http://www.ucsusa.org/assets/images/global_warming/graph_hurricaneinten…
".... initial findings suggest that over the period 1970 to 2004 warmer sea surface temperature is the major factor in the increase in category 4 to 5 hurricanes globally.(19, 20)
Footnotes (they're hot links there, they do understand HTML, if not text) are:
(19) Hoyos, C.D., P.A. Agudelo, P.J. Webster, and J.A. Curry. 2006. Deconvolution of the factors contributing to the increase in global hurricane intensity. Science 312:94-97.
(20) Santer B.D., T.M.L. Wigley, P.J. Geckler, C. Bonfils, M.F. Wehner, K. AchutaRao, T.P. Barnett, J.S. Boyle, W. Brüggemann, M. Fiorino, N. Gillett, J.E. Hansen, P.D. Jones, S.A. Klein, G.A. Meehl, S.C.B. Raper, R.W. Reynolds, K.E. Taylor, and W.M. Washington. 2006. Forced and unforced ocean temperature changes in Atlantic and Pacific tropical cyclogenesis regions. Proceedings of the National Academy of Sciences.
Conclusion --- the science page they put up is being done by some trendy web designer who doesn't think reading is very important and doesn't do it well.
Grumble.
Oh, did I forget my coffee again? That might help ....
It's hard to define a "good source." The so-called best track data has serious problems, in part because of the inconsistencies in its creation. It has been used (the UCS site uses a figure that used it to argue for a large global increase in Cat 4 and 5 storms), but the results are plagued by the problems in the datasets. The Kossin et al. (2007) paper is the only globally-consistent analysis, using satellite data.
http://www.ssec.wisc.edu/~kossin/articles/Kossin_2006GL028836.pdf
The ACE index has some interesting numbers, but it appears SST is only marginally significant to the numbers.
The reference about doubling of cat 4/5s is from the original Webster team paper (although Hoyos may have repeated the information): "(H)urricanes in the strongest categories (4 + 5) have almost doubled in number (50 per pentad in the 1970s to near 90 per pentad during the past decade) and in proportion (from around 20% to around 35% during the same period). These changes occur in all of the ocean basins."
Regarding the Kossin paper, I seem to recall knives being sharpened the moment it became available. As the Wabbit says, pass the popcorn.