Roger Pielke has co-authored a new paper on hurricanes and global warming. The paper itself is here, though it's also worth reading his comments on Prometheus. There's an excerpt below:

. . . claims of linkages between global warming and hurricanes are misguided for three reasons. First, no connection has been established between greenhouse gas emissions and the observed behavior of hurricanes (IPCC 2001; Walsh 2004). Yet such a connection may be made in the future as metrics of tropical cyclone intensity and duration remain to be closely examined. Second, a scientific consensus exists that any future changes in hurricane intensities will likely be small in the context of observed variability (Knutson and Tuleya 2004, Henderson-Sellers et al 1998), while the scientific problem of tropical cyclogenesis is so far from being solved that little can be said about possible changes in frequency. And third, under the assumptions of the IPCC, expected future damages to society of its projected changes in the behavior of hurricanes are dwarfed by the influence of its own projections of growing wealth and population (Pielke at al. 2000). While future research or experience may yet overturn these conclusions, the state of knowledge today is such that while there are good reasons to expect that any connection between global warming and hurricanes is not going to be significant from the perspective of event risk, but particularly so from the perspective of outcome risk as measured by economic impacts.