I googled for quotes and found these
"The voluminous evidence now strongly suggests that unless we act boldly and quickly to deal with the underlying causes of global warming, our world will undergo a string of terrible catastrophes, including more and stronger storms like Hurricane Katrina, in both the Atlantic and the Pacific."
"For example, when we were first warned that the levees were about to break in New Orleans because of Hurricane Katrina, those warnings were ignored. Later, a bipartisan group of members of Congress chaired by Representative Tom Davis (R-VA.), chairman of the House Government Reform Committee, said in an official report, "The White House failed to act on the massive amounts of information at its disposal," and that a "blinding lack of situational awareness and disjointed decision-making needlessly compounded and prolonged Katrina's horror.""
So what part are you pointing at? I don't see that he actually said "Katrina is a result of global warming" and the idea that warmer oceans leads to more frequent and more intense hurricanes is pretty straightforward.