Kerry Emmanuel, one of the most prominent of researchers into the connection between climate change and hurricanes, edited a just-released study of hurricanes in PNAS that looks at hurricane magnitude and risk in a new way, by storm surge instead of wind speed or reported damaged, and finds that "Statisically downscaling 21st century warming patterns from six climate models results in a twofold to sevenfold increase in the frequency of Katrina magnitude events for a 1 degree Celsius rise in global temperature."
It's a complicated study, that looks at various measures of "skill" relating to hurricanes, including teleconnections such as ENSO, but concludes that "With a few notable exceptions, global average surface temperature is a better predictor of Atlantic cyclone activity (as measured by the surge index) than grid cell temperatures from almost anywhere else on Earth."
Most alarming:
The response to a 1 degree Celsius warming is consistently an increase by a factor of 2-7. [] All tests indicate confidence in the factor 2-7 increase in the number of Katrina magnitude surges for each degree of global warming. This increase does not include the additional increasing surge threat from sea level rise.
The study concludes by saying, in effect, we have crossed the climate Rubicon:
We find that .4 degree Celsius global average warming results in a halving of the return period of Katrina magnitude events. This is less than the warming over the 20th century. Therefore, we have probably crossed the threshold where Katrina magnitude surges are more likely caused by global warming than not.
The study, by Grinsted et al, also mentions the previous questions that arose regarding global warming and hurricanes, in particular the possibility that even if physics tells us that a warming world will produce stronger tropical cyclones, that increased wind shear might mean fewer hurricanes, period.
But the projections don't bear that theory out.
Quite the contrary. The denier crowd tries to wave it off here.
Kit Stolz 