There are more storm losses because insurance companies are writing more policies on more risky property without collecting appropriate premiums.
Moreover, the study Munich Re cites can’t differentiate between natural and manmade climate change:
The study was not able to conclusively differentiate in the climatological forcing of loss changes between the natural and the man-made components of climate change.
Rahmstorf is not quite a wholly-owned subsidiary of Munich Re:
http://www.google.com/search?q=Rahmstorf+%22Munich+Re%22