Global warming caused this? Here's another theory:

This confluence of optimal ocean and atmosphere conditions has been known to produce increased tropical storm activity in multi-decadal (approximately 20-30 year) cycles. Because of this, NOAA expects a continuation of above-normal seasons for another decade or perhaps longer. NOAA's research shows that this reoccurring cycle is the dominant climate factor that controls Atlantic hurricane activity. Any potentially weak signal associated with longer-term climate change appears to be a minor factor.

The multi-decadal signal that has contributed to increased Atlantic activity since 1995 has also produced a marked decrease in hurricanes in the eastern Pacific hurricane region. Similar conditions also produced very active Atlantic hurricane seasons during the 1950s and 1960s. In contrast, the opposite phase of this signal during 1970-1994 resulted in only three above-normal Atlantic hurricane seasons in the entire 25-year period.
http://www.sciencedaily.com/releases...0805064901.htm