Updated: A Universal Hurricane Frequency Function - Ready For Some Hot Climate Action?


Number of storms predicted per year during the period 1854 -- 2006 versus
numbers actually observed for the Atlantic (filled diamonds). The model predictions
(grey curve) have been normalized to the data. A quadratic fit to the model is shown for
the period 1960 -- 2006.
Image and caption credit:Erlich, Atmospheric and Oceanic Physics; arXiv

Robert Ehrlich, a physicist at George Mason University in Washington DC, has published a paper demonstrating that just two variables, surface temperature of the sea and latitude, can account for the probability density of a hurricane or tropical storm forming. 'No other factors need be taken into account' is a fair characterization. The entire paper is available as a pdf file download here. (Those who consider themselves mathematically challenged may not want to bother.)Technology Review has the best money quote I've seen regarding this work.

The exponent of 3.5 in Ehrlich's power law means that numbers of hurricanes should increase sharply as the world warms and much more dramatically than climatologists have been expecting. His prediction is that a 2 degree C increase in average temperature will lead to an 11-fold increase in the number of hurricanes.
Note for aligators and algore haters. Ocean surface temp, a most critical variable, is a function of regional weather on the scale of, say, the Gulf of Mexico - much more than just the 'CO2 blanket.' Important variables which control ocean surface temperature in the Gulf would include:

  • daytime solar radiation at water surface

  • night cloud cover

  • wind and wave generated turbulence (leading to mixing and convective heat loss)

  • turbidity (cloudiness of water)

  • temperature and flow of influent Mississippi River water

  • evaporative heat loss


So the question becomes, would it be worth trying to better measure, model and more accurately project seasonal ocean temps in the Gulf of Mexico? Would people think or behave any differently if the results were shown be within high confidence limits? Would such projections convince the alligators that climate action is a worthy investment? Probably not.

Updates: Atlanta Journal Constitution has a story on a new 'consensus study' by a diverse group of meteorologists and climate scientists that begins: "Top researchers now agree that the world is likely to get stronger but fewer hurricanes in the future because of global warming, seeming to settle a scientific debate on the subject." The story's lead-in obviously contradicts Erlich's work as discussed in this post and elsewhere. I wonder if the the AJC reporter got it right?

One more item. I forgot to add to the list a potentially very important variable affecting ocean surface temperature in the Gulf. Once a tropical storm has entered the Gulf, seiche and wave action will increase overall water turbulence. This added movement could break up thermal stratification which keeps hottest water floating on the top, where it's energy contributes to hurricane formation. In other words, following entrance of a tropical storm into the Gulf, the ocean's surface heat would take longer to build up to the point where subsequent hurricane could be triggered - a possible frequency limiting factor.

More on Hurricanes
Where Do Hurricanes Come From?
Hurricane Destruction... Have We Only Just Begun?
Sewage As Hurricane Protection? New Orleans Could Use It To Regrow Wetlands
Ocean's Color Can Change Hurricane Patterns
How Will Future Hurricanes Respond to Climate Change?

Tags: Atlantic

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