Katrina allowed the general public to make the link between global warming and the possible consequences for individuals-- to (tele)visualise the problem

Yeap, and for the same reason after we got one year without hurricanes, for the American public GW no longer exists.

Indeed.  The thinking from the lab is that humans over-focus on 'recency'-- see Amos Tversky, Daniel Kahneman and Kahneman's Nobel Prize, also humans focus on what is 'representative' and then over-generalise.  Which makes taking on a long term problem very, very difficult.

http://www.realclimate.org/index.php/archives/2006/07/its-different-in-europe/

if you follow the link and go to the middle of the page on that link, there is a fascinating discussion

http://www.sej.org/pub/index4.htm

of why European and American views of GW are so different.
The bottom line, our media just doesn't treat the climate change sceptics with the same level of respect.

( http://environment.guardian.co.uk/climatechange/story/0,,1875762,00.html might be a reason why ;-)

  Here in the UK, we have just had the right wing political party spend 2 days at its conference discussing green taxes.  Now in practice they voted not to have them and I am sceptical anything that really affected our freedom to go on weekend flights to Europe, etc., is really on the table.

But still, it is unimaginable that 'Republicans against Global Warming' would emerge and be a vibrant voice in the party.

(except your mayor Bloomberg.  Since Republicans arguably invented the environmental movement in the USA (Theodore Roosevelt), there might be a buried momentum there).