So here we go!
Essentially, he resigned because another scientist on IPCC spoke at a Harvard conference and said "experts to warn global warming likely to continue spurring more outbreaks of intense hurricane activity". This after Dr. Landsea was asked to analyse recent hurricane activity in the Atlantic, which he did, and where his conclusion was that "no reliable, long-term trend up in the frequency or intensity of tropical cyclones" can be extrapolated from the data.
IPCC's own previous assesments in 1995 and 2001 also concluded that there was no global warming signal found in the hurricane record.
So he is resigning because the political corectness requires that one "believes" in global warming existing and causing all sorts of havoc in weather patterns. Even if results of scientific research have to be misstated or ignored, some people will do that. So he quit. Good for him.