My paper on this subject will finally appear in the Journal of Climate soon. You can see it’s status (temporarily, anyway) at this link.
You can download the paper here.
The gist is that the evidence shows that hurricanes have not increased in either number of intensity in the North Atlantic. I’ve only used data through 2006; which is to say, not this year’s. But if I were to, then, since the number and intensity of storms this past year were nothing special, the evidence would be even more conclusive that not much is going on.
Now, I did find that there were some changes in certain characteristics of North Atlantic storms. There is some evidence that the probability that strong (what are called Category 4 or 5) storms evolving from ordinary hurricanes has increased. But, there has also been an increase in storms not reaching hurricane level. Which is to say, that the only clear signal is that there has been an increase in the variability of intensity of tropical cyclones.
Of course, I do not say why this increase has happened. Well, I suggest why it has: changes in instrumentation quality and frequency since the late 1960s (which is when satellites first went up, allowing us to finally observe better). This is in line with what others, like Chris Landsea at the Hurricane Center, have found.
I also have done the same set of models of global hurricanes. I found the same thing. I’m scheduled to give a talk on this at the American Meteorological Society’s annual meeting in January 2008 in New Orleans. That paper is here.