A few weeks ago I saw Tom Knutson of NOAA’s GFDL lab give an overview talk on the current state of the debate over hurricanes and global warming. His overview slide had the following text, which I also found on his NOAA homepage:

Two frequently asked questions on global warming and Atlantic hurricanes are the following:

i) Have humans already caused a discernible increase in Atlantic hurricane activity?
ii) What changes in Atlantic hurricane activity are expected for the late 21st century, given the pronounced global warming scenarios from current IPCC models?

In this review, I address these questions in the context of published research findings. My conclusions are:

i) It is premature to conclude that human activity–and particularly greenhouse warming–has already had a discernible impact on Atlantic hurricane activity.

ii) It is likely that greenhouse warming will cause hurricanes in the coming century to be more intense on average and have higher rainfall rates than present-day hurricanes.

Here is what we wrote in a 2005 review of the literature (PDF):

To summarize, claims of linkages between global warming and hurricane impacts are premature for three reasons. First, no connection has been established between greenhouse gas emissions and the observed behavior of hurricanes (Houghton et al. 2001; Walsh 2004). Emanuel (2005) is suggestive of such a connection, but is by no means definitive. In the future, such a connection may be established [e.g., in the case of the observations of Emanuel (2005) or the projections of Knutson and Tuleya (2004)] or made in the context of other metrics of tropical cyclone intensity and duration that remain to be closely examined. Second, the peer-reviewed literature reflects that 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 et al. 2000). While future research or experience may yet overturn these conclusions, the state of the peer-reviewed knowledge today is such that there are good reasons to expect that any conclusive connection between global warming and hurricanes or their impacts will not be made in the near term.

Looks like that assessment is holding up quite well.

Reference: Pielke, Jr., R. A., C. Landsea, M. Mayfield, J. Laver and R. Pasch, 2005. Hurricanes and global warming, Bulletin of the American Meteorological Society, 86:1571-1575. (PDF)