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.
This is a great little post, Jamais. It demonstrates for me why Americans society seems to have such a hard time with scientific inquiry and analysis: it doesn't easily support beliefs. Beliefs, as Lakeoff suggests, are much more important than facts. Susan Strong, at the Metaphor Project has a recent post to her subscribers that appeals to the progressive camp to leverage the belief of 55% of Americans that global warming was somehow responsible for Katrina's fury:
It is also newly clear to the mainstream public that real homeland security involves energy, food, and water security, as well as social justice, and maybe even a bit more inclination to question THE IRAQI DISASTER.
SO WE PROGRESSIVES CONCERNED ABOUT PEACE, JUSTICE AND ECOLOGICAL - SOCIAL SUSTAINABILITY SHOULD RIGHT NOW BE MAKING UP LISTS OF ALL OF THE NEW POLICIES OUR COUNTRY NEEDS AND REFRAMING THEM AS THE ESSENTIALS OF REAL HOMELAND SECURITY. For example, we could be pointing out that real homeland security means protecting the green belts around our cities where food could be grown if need bethat food security is a big part of real homeland security. REPLACE THE WORD SUSTAINABLE IN YOUR LEXICON WITH REAL HOMELAND SECURITY FOR NOW. (See last section for my answer to objection to this advice.) In conversation, you can begin by asking the question, WHATS REAL HOMELAND SECURITY NOW