Revisting Category 4&5 Tropical Cyclones…Again

A little less than a year ago, I updated my work examining whether there has been any increase in the number of category four and five tropical cyclones, first in the Northern Hemisphere and then, more cautiously, the entire world since 1987 (that is, when aircraft reconnaissance ceased in the Northern West Pacific Basin) (in the case of the Southern Hemisphere, this means the 1987-88 season at the start). Well I figure now is as good a time as any to update to include the year 2011 in the analysis (the 2010-2011 season for the Southern Hemisphere.

First, there is the Northern Hemisphere data:

As you can see, 2011 was a slightly above average year in terms of the number of category four and five storms in the Northern Hemisphere (in terms of overall activity it was still below average). Nevertheless, the trend remains ever so slightly negative which is contrary to the hypothesis that the number of such storms would increase with higher sea surface temperatures. But what about the world? Well, as mentioned before, because the Southern Hemisphere seasons occur during the end of one year and the beginning of the next, it is difficult to combine seasons. So I did it two ways: in one time series I added the Southern Hemisphere seasons to the Northern Hemisphere totals in the year associated with the beginning of their season, while in the other added them to end year time series.

Here they are, in green and red, respectively:

The conclusion with respect to the global data is even stronger now than last year: there are no trends! The slight positive trend in the green time series has vanished, in fact it appears it is now very, very slightly negative; the red trend is still very slightly negative. So I remain confident in my initial assessment of this data: there is no evidence that higher sea surface temperatures are increasing the number of strong tropical cyclones.


2 Responses to “Revisting Category 4&5 Tropical Cyclones…Again”

  1. None Says:

    Well, as I understand it, the surface sea temperature has not been rising over the past 5-10 years, and Pielke frequently requests clarification from the climate community of what has happened to the missing heat (I’d also like to know).

  2. timetochooseagain Says:

    None-These data cover the period from 1987-2011, or 25 years, over which there has been a significant accumulation of ocean heat and sea surface temperature trend, so this period should be sufficient to establish whether there has been any observable effect of warming on the number of intense storms: the answer is pretty unambiguously no. Of course, some effect might emerge eventually. Models suggest the hypothetical increases in intensity might be measurable after several more decades. I intend only to rebut the idea that the effects is already large and observable, which should be clear from my original post.

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