The current issue of Science has an article about tropical cyclones in a warming world. It can be found on the Science site [LINK], or on Peter Webster's web site [LINK]. Here's the info:
Webster, P.J., G. J. Holland, J. A. Curry, and H.-R. Chang, 2005: Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment, Science, 309 (5742), 1844-1846.
The findings are actually not too surprising given the recent studies reported here and all over the news. The study looks at the last 30+ years of tropical cyclone frequency and intensity and does a statistical analysis of it, comparing it to SST. There is a warming SST throughout the tropics, but there doesn't seem to be a significant relationship to more frequent cyclones, except in the north Atlantic. However, there is a significant trend toward more intense cyclones (category 4 and 5) over the same time and in all parts of the tropics. The maximum intensity isn't increasing, at least as measured by maximum wind speed, but there are more and more big cyclones.
For those of you who don't mind reading technical writing, check out the article. It has lots of references to other relevant work, including the scientific basis for the controversy over this topic.
The authors can't rule out long-term oscillations as the cause of the trend, but their statisitics seem to point to a much longer period than the literature has usually found in cyclone activity. The conclusion is that the number of hurricanes doesn't seem to be related to the warming SSTs (and thus global warming), but the strength of those hurricanes is increasing, and is probably related to global warming. This is important for people because it tells us that we need to prepare for more Katrina-like storms in the future; not just in New Orleans, but across the entire gulf coast and southeastern coast. Other parts of the world also need to prepare for more large hurricanes, like Japan, Taiwan, and Mexico.