GW and Hurricanes

A new paper on global warming and hurricanes came out the day of the NAS report, but it got a little lost in the shuffle. From the press release:

Global warming accounted for around half of the extra hurricane-fueling warmth in the waters of the tropical North Atlantic in 2005, while natural cycles were only a minor factor, according to a new analysis by Kevin Trenberth and Dennis Shea of the National Center for Atmospheric Research (NCAR)....

"The global warming influence provides a new background level that increases the risk of future enhancements in hurricane activity," Trenberth says....

The study contradicts recent claims that natural cycles are responsible for the upturn in Atlantic hurricane activity since 1995. It also adds support to the premise that hurricane seasons will become more active as global temperatures rise.

They have some hard data behind them:

By analyzing worldwide data on sea-surface temperatures (SSTs) since the early 20th century, Trenberth and Shea were able to calculate the causes of the increased temperatures in the tropical North Atlantic. Their calculations show that global warming explained about 0.8 degrees F of this rise. Aftereffects from the 2004-05 El Nino accounted for about 0.4 degrees F. The Atlantic multidecadal oscillation (AMO), a 60-to-80-year natural cycle in SSTs, explained less than 0.2 degrees F of the rise, according to Trenberth. The remainder is due to year-to-year variability in temperatures.