The IPCC and others have long pointed out that the number of hurricanes making landfall has not been trending upwards. Regarding the Atlantic in particular, the IPCC said "it is unlikely that annual numbers of tropical storms, hurricanes and major hurricanes counts have increased over the past 100 years in the North Atlantic basin." But will the hurricanes that do form get worse? Climate models project that they will. Er, well, some do. Turns out some project that they will cause hurricanes to get less intense. Which complicates the task of testing predictions against reality.
The available data indicate that the strongest Atlantic hurricanes have gotten more intense since 1970. That result is what scientists want to explain. Al Gore of course claims to know: greenhouse gases cause global warming which causes warmer oceans which causes stronger storms. Simple. But if we want some actual insight into the matter, we have to look at the climate system in all its complexity.
So a group of experts studied how climate models represent hurricane formation conditions and how they might be affected by increased greenhouse gases. They were able to find models that indicated that rising greenhouse gas levels would lead to conditions in which hurricanes get more intense. But greenhouse gases aren't the only things going into the air: other pollutants called aerosols go as well, and the combined effects of both in some models lead to less intense hurricanes.
This complexity not only makes forecasting tricky, it also means you can't explain the past. If your model says historical emissions of greenhouse gases and aerosols should have reduced hurricane intensity, and it instead went up, what does that imply about your model? And if someone else's model says hurricane intensity actually should have gone up, what does that tell you about the state of your science, when both of you claim to be working from the same theory but predict the opposite conclusions?
We don't say so to cast aspersions on the scientists. They're trying their best to figure out very complicated things and are taking data seriously even when it’s not confirming their theories. But feel free to cast aspersions on any politician who claims to know that your SUV is responsible for the next hurricane, whenever it hits, and however strong it turns out to be.