Well, I am going to have to eat some crow.
Back in early October, I unwisely predicted there would be 18 Category 4 or 5 hurricanes globally in the year 2007. At the time, there had been 14. Since then there has only been one more the incredibly devastating Cyclone Sidr bringing the global total to 15. And with the year almost out, at this point I don't see any chance of not being wrong in my prediction.
In fact and as we'll see barring some sudden dramatic tropical eruption, 2007 is going to turn out to be a below-average year for overall global intense hurricane activity. That's not to say there weren't some serious hotspots particularly the North and South Indian Ocean basins. But for anyone convinced that global warming is causing an increase in the intensity of the average hurricane, it's hard to make the case that 2007 serves as a data point in your favor.
To see that, though, let's first survey the total storm activity in all the major hurricane basins. My source for this data is Unisys Weather, but I have made a few corrections in places where that data seem incorrect (e.g., Cyclone Indlala is only listed as a tropical storm by Unisys when in fact it was a Category 4).
In the Atlantic and Northeast Pacific, where storms are tracked by the U.S. National Hurricane Center, I counted all storms that were given names (which occurs once the storms reach maximum sustained wind speeds of 35 knots 40 mph or higher, the cutoff for Tropical Storm status). For other basins, where there are multiple measurements used in classifying storms and multiple monitoring agencies, I am counting all storms in the Unisys database that had a maximum sustained wind speed of 35 knots or higher.
That process leaves you with the following numbers, as of Dec. 19, 2007:
Tropical Storm Tracks, 2007 Northwest Pacific Basin Unisys Weather
What can we read into these numbers?
Well, first off, the average total number of storms per year is generally in the 80-90 range, so there's nothing particularly noteworthy about 2007 in that respect.
However, when you come to the total number Category 4 and 5 storms, it's another story entirely. Here, the average per year is 17, and the record in one year is 25. By these lights, 2007 is definitely a below average year.
Granted, 2004, 2005, and 2006 were all above average, with 23, 22, and 19 Category 4 and 5 storms, respectively. So 2007 may just be a quiet anomaly. Moreover, there were a number of borderline Category 3/Category 4 storms this year, which might have been bumped up a category had they occurred in the Atlantic region.
But nevertheless, the official 15 storm total which, to be sure, could increase by the end of the year, but probably not by more than one storm at the absolute most clearly does not help the argument that global warming is intensifying hurricanes.
Next week I will go more in depth, and look in more detail at some of the most remarkable and troubling storms of 2007.
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