The connection between climate disruption and Katrina is a complex issue, one that is ill-served by either bald assertions that global warming "caused" the hurricane or talking point-driven claims that any suggestion of a link amounts to "politicizing" the disaster.
As we've noted here, the connection between global warming and hurricanes looks to be one of increased average intensity -- but not something allowing simple, "if-then" logic for any single event. But we're not climate professionals; you're better off hearing from people who are experts in the field. I mean, of course, the scientists at the RealClimate website.
In Hurricanes and Global Warming -- Is There A Consensus? the RealClimate authors give a painstaking breakdown of the factors that could contribute to increased hurricane intensity. Their conclusion won't satisfy partisans, but gives a good read on where the science is these days: Thus, we can conclude that both a natural cycle (the AMO [Atlantic Multidecadal Oscillation, or Hurricane Cycle]) and anthropogenic forcing could have made roughly equally large contributions to the warming of the tropical Atlantic over the past decades, with an exact attribution impossible so far.








