The Greater Miami Chapter of the AMS presents
Hurricanes and Global Warming

Friday, March 25, 2011 at 10:30 AM.
Refreshments 10:15 AM

AOML 1st floor Conference Room
4301 Rickenbacker CSWY
Miami, FL


Bill Gray
Colorado State University
Ft. Collins, CO

"Hurricanes and Global Warming"

is global warming causing more or stronger hurricanes? Or is the effect of climate change negligible with regard to tropical cyclones? Well, the answer to this question is still being actively debated. No doubt, the link between hurricanes and global warming is of great interest to our society - especially for us here in South Florida!

The Greater Miami Chapter of the AMS is fortunate to have Prof. Bill Gray (Colorado State University) as a guest speaker. He is a pioneer in the science of forecasting hurricanes and one of the world's leading experts on tropical storms. I'm sure many of you will know Dr. Gray from his seasonal hurricane forecasts, which draw considerable media attention upon their release every April.

Minutes of the March 25, 2011 meeting of the
Greater Miami chapter of the
American Meteorological Society
held in the first floor conference room of
NOAA's Atlantic Oceanographic
and Meteorological Laboratory

The meeting began at 10:30 AM with Dr. Frank Marks welcoming the 50 guests present as well as those monitoring the GoToMeeting live webcast of the seminar. He introduced chapter president Falko Judt, who introduced our speaker Dr. William Gray, professor emeritus of Colorado State University. Dr. Gray's talk was entitled "Tropical Cyclones and Global Warming." He began by relating his early experiences as an Air Force forecaster stationed in the Azores in the early 1950s and how prognostications for trans-Atlantic flights had to be based on minimal information and soundings. In the mid-1950s he began graduate studies at the University of Chicago under Dr. Herbert Riehl which led him to become involved with the National Hurricane Research Project and its pioneering research flights into hurricanes.

He then addressed the main topic of his discussion, starting with Dr. Kerry Emanuel's 2005 paper relating sea surface temperature (SST) to the Potential Dissipation Index for tropical cyclones. Dr. Gray showed that there was no relationship between SSTs and the Accumulated Cyclone Energy (ACE) index for the Northwestern Pacific and Atlantic and that Klotzbach (2006) showed that global ACE has decreased from 1990-2000 while SST in the Main Development Region was rising.

Turning to Webster el al (2005) which purported a doubling of Category 4 & 5 tropical cyclones over a 30 year period, Dr. Gray contended that tropical forecast centers around the world lacked adequate satellite capability to categorize these high end storms during the early period of the study causing an upward bias in the number of major storms categorized over the three decades. Despite these deficiencies Webster el al was widely reported and used to support the contention that recent global temperature trends were responsible for increased in Atlantic hurricane activity. Holland and Webster published a second paper in 2007 expressing their confidence in the trend they had illustrated. Trenberth and Shea (2006) said the Atlantic ThermoHaline Circulation (THC) was NOT responsible for record high temperatures. And Sanders et al (2006) held that rises in sea temperatures cannot be due solely to natural climate variations.

Gray sent letters to editors of journals publishing these studies taking exception to them pointing out errors, but they were rejected and not printed. In contrast, Ryan Maue graphed global ACE which demonstrated a decrease over the last decade. And Gray's study of annual tropical weather budgets estimates that the .65 Watts/meter increase attributed to CO2 increases from 1975-2010 is well within the noise level of seasonal changes in these energy budget. Gray then sought to invalidate the assumption that rising SSTs bring about an increase in vertical lapse-rate buoyancy on a climate-scale. But entrainment limits buoyancy so that small increases in atmospheric warming would not lead to increases in overall convective activity.

In the NOAA Climate Workshop in 1996, Gray forecast that changes in Atlantic SST patterns associated with the THC would cause an increase in Atlantic hurricane activity, such as the 1945-1969 period. With increases in global temperature there has been no upward trend in landfalling major hurricanes in the US and the Eastern US coastline. Instead, variations in Atlantic hurricane activity on a decadal-scales follow changes in the THC. This offers a better explanation in changes in hurricanes than CO2 increases or small increases in global temperature.

Submitted by
Neal Dorst
acting chapter secretary

Recorded presentation of Dr. Gray's seminar is available here

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