I caution against blaming Katrina on global warming, as does Ross Gelbspan (generally a good environmental journalist). Granted, oil and energy policies should change, but Arthur Waskow overplays the Katrina card.
See the analysis, links and debate at RealClimate. Here's a scientific paper on hurricanes and climate change courtesy of Prometheus. Gristmill debates this connection, too. (Cp. enviro law who sees a connection.)
My 2 cents is that there is a macro relationship but we are too prone to articulate a spurious correlation.
For a halakhic argument regarding climate change, see Eliezer Diamond's paper. The Harvard publisher claims:
He convincingly argues that halakhic reasoning about notions of conventionality and equity in environmental matters could be applied meaningfully to the problem of global warming. Such application requires a careful analysis of concrete human situations as well as a creative analysis of Jewish legal sources.
My own tongue-in-check post on energy policy and halakhah here.
While here I've looked the global warming connection, other Jewish bloggers properly compare Katrina to the tsunami (Mystical Politics) and refute Jews who connect hurricane Katrina's refugees to divine punishment for Israel's evacuation of Gaza (DovBear, Hirhurim, Miriam at Bloghead, and Orthomom). Cp. Christians who say that Katrina is divine retribution New Orleans and gays. Hat tip Gristmill.