In Al Gore's Oscar- and Nobel Prize-winning movie, An Inconvenient Truth, he makes (among other things) the assertion that Hurricane Katrina was in part caused by human-induced global warming.
Al's famous graph of carbon dioxide in the atmosphere shows a nice smooth upward trend, as does its accompanying graph of global temperatures. Hurricanes form in warm waters, and gain energy from heat. Therefore, global warming will cause more hurricanes, and of increased intensity, causing untold destruction to low-lying and coastal areas - as in Katrina. Indeed, the official poster for the movie shows a monster hurricane swirling out of a polluting smokestack.
So, we can expect monster hurricane strikes on the United States to become a regular event, eh? Let's take a look at the record. Here we see... almost the exact opposite. Hurricane activity clearly reached a peak in the 40s, and has gone generally down from there. 2005 represented a spike, followed by a trough in 2006. Although the 2007 hurricane season is not yet over, it certainly hasn't been a very active one either.
In fact, the lack of hurricanes is causing significant problems. The USDA's Drought Map shows Exceptional Drought - the highest category - over a tremendous swath of the Southeast, surrounded by large areas of Extreme and Severe drought. Including all the various drought notations, the entire Southeastern region is in drought, except for a small chunk of Georgia and Florida. Atlanta now has less than three month's supply of water left. Georgia as a whole as received only just over half the average rainfall at this point in the year - not even nine inches.
Which is just about what you get from... one hurricane! If we had been receiving hurricanes on schedule, we would not be having a drought. Al Gore's prediction has been entirely wrong, so much so that farmers on TV have been heard almost wishing that a hurricane would come their way. Time to fire up the SUV for a nice long drive?