The link between events such as Typhoons Haiyan and Katrina and climate change is clearly explained by Dr Peter Stott, lead author on IPCC report, on Radio 4 Today programme,12/11/13 (6.53.39 am). His conclusion: events are directly affected by climate change which causes increases in force and severity.
The iPlayer link is http://www.bbc.co.uk/iplayer/episode/b03h2nqw/Today_12_11_2013/