That said, a growing number of climate researchers think that such a case is now being made.
MIT's Kerry Emanuel has published a piece in Nature arguing that, although research trying to link hurricane frequency with global warming has yet to find a connection, the same is not true for hurricane intensity:
Here I define an index of the potential destructiveness of hurricanes based on the total dissipation of power, integrated over the lifetime of the cyclone, and show that this index has increased markedly since the mid-1970s. This trend is due to both longer storm lifetimes and greater storm intensities. I find that the record of net hurricane power dissipation is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multi-decadal oscillations in the North Atlantic and North Pacific, and global warming. My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential, and—taking into account an increasing coastal population—a substantial increase in hurricane-related losses in the twenty-first century.
(Although the Nature article is, as usual, behind a subscriber barrier, New Scientist has a good summary.)
Emanuel's work is not the definitive research on the subject; as the New Scientist article notes, there remains some questions about how Emmanuel adjusted historical wind speeds to match current methods. That said, the research fits well with simulations from the National Oceanic and Atmospheric Administration's "Geophysical Fluid Dynamics Laboratory," testing connections between global warming and hurricane strength.
Moreover, NOAA projections for the 2005 hurricane season suggest that this could be among the busiest hurricane seasons on record. They give a 95% likelihood of 18-21 tropical storms (10 is average, 21 the most ever recorded), 9-11 hurricanes (5 is average, 12 the most ever), 5-7 being Category 3 or higher (only 2 Category 3+ is average, 8 is the most ever).
It's important to note that we are in the midst of the high end of the multi-year hurricane cycle, so we would be seeing above average hurricane numbers regardless. Nobody is claiming that global warming has caused us to have more hurricanes than average. But what we need to bear in mind is that global warming can modify the effect of existing climate cycles. So even if climate disruption doesn't cause the number of hurricanes to exceed historical trends, the Emmanuel and GFDL research suggest that the above-average number of storms could, in turn, be stronger than they otherwise would be.
Research such as that done by Kerry Emanuel and NOAA is high on the list of reasons why normally sober and cautious organizations such as banks and insurance companies are often on the forefront of environmental and climate issues. The difference between a Category 2 and a Category 4 hurricane isn't simply wind speeds of 96-110 mph versus 131-155 mph; the bigger difference is the millions of more dollars in damage done by the more powerful storms, the hundreds or thousands of more homes destroyed, and the dozens of more lives lost.
Only one 'm' in Emanuel :-)
We had a sciscoop article on this last week, going into some of the technical issues.
Fixed. Thanks for the link, Arthur.