How does the frequency of occurrence of Atlantic basin hurricanes respond to increases in temperature? In exploring this important question within the context of the warming that occurs in going from La Niņa conditions to El Niņo conditions, Wilson (1999) utilized data from the last half of the 20th century in determining that the probability of having three or more intense hurricanes was only 14% during an El Niņo year, but fully 53% during a La Niņa year. Hence, the probability of experiencing three or more intense Atlantic basin hurricanes when going from a cooler La Niņa year to a warmer El Niņo year actually drops, from a hefty 53% to a mere 14%, or to only about a quarter of what the probability of occurrence was before the temperature increase occurred.
Muller and Stone (2001) conducted a similar study of tropical storm and hurricane strikes along the southeast U.S. coast from South Padre Island (Texas) to Cape Hatteras (North Carolina), using data from the entire past century. For tropical storms and hurricanes together, they found an average of 3.3 strikes per La Niņa season, 2.6 strikes per neutral season, and 1.7 strikes per El Niņo season. For hurricanes alone, the average rate of strike occurrence ranged from 1.7 per La Niņa season to 0.5 per El Niņo season, which represents a frequency-of-occurrence decline of fully 70% in going from cooler La Niņa conditions to warmer El Niņo conditions. Likewise, Elsner et al. (2001) - who also worked with data from the entire past century - found that when there are below normal sea surface temperatures in the equatorial Pacific, "the probability of a U.S. hurricane increases."
Lyons (2004) also conducted a number of analyses of U.S. landfalling tropical storms and hurricanes, dividing them into three different groupings: the 10 highest storm and hurricane landfall years, the 9 lowest such years, and all other years. These groupings revealed, in Lyons' words, that "La Niņa conditions occurred 19% more often during high U.S. landfall years than during remaining years," and that "El Niņo conditions occurred 10% more often during low U.S. landfall years than during remaining years." In addition, it was determined that "La Niņa (El Niņo) conditions were 18% (25%) more frequent during high (low) U.S. landfall years than during low (high) U.S. landfall years."
An analogous approach was used by Pielke and Landsea (1999) to study the effect of warming on the intensity of Atlantic basin hurricanes, using data from the period 1925 to 1997. In their analysis, they first determined that 22 years of this period were El Niņo years, 22 were La Niņa years, and 29 were neither El Niņo nor La Niņa years. Then, they compared the average hurricane wind speed of the cooler La Niņa years with that of the warmer El Niņo years, finding that in going from the cooler climatic state to the warmer climatic state, average hurricane wind speed dropped by about 6 meters per second.
Independent confirmation of these findings was provided by Pielke and Landsea's assessment of concurrent hurricane damage in the United States: El Niņo years experienced only half the damage of La Niņa years. And in a ten-year study of a Mediterranean waterbird (Cory's Shearwater) carried out on the other side of the Atlantic, Brichetti et al. (2000) determined - contrary to their own expectation - that survival rates during warmer El Niņo years were actually greater than during cooler La Niņa years.
In another pertinent study, Landsea et al. (1998) analyzed the meteorological circumstances associated with the development of the 1995 Atlantic hurricane season, which was characterized by near-record tropical storm and hurricane activity after four years (1991-94) that had exhibited the lowest such activity since the keeping of reliable records began. They determined that the most important factor behind this dramatic transition from extreme low to extreme high tropical storm and hurricane activity was what they called the "dramatic transition from the prolonged late 1991-early 1995 warm episode (El Niņo) to cold episode (La Niņa) conditions."
Last of all, in a 20th century changepoint analysis of time series of major North Atlantic and U.S. annual hurricane counts, which in the words of its authors, "quantitatively identifies temporal shifts in the mean value of the observations," Elsner et al. (2004) found that "El Niņo events tend to suppress hurricane activity along the entire coast with the most pronounced effects over Florida."
The obvious conclusion to be drawn from the results of these several studies, which is clearly contrary to that espoused by the majority of the world's climate alarmists, is that global warming does not lead to either more frequent or more intense Atlantic basin hurricanes. In fact, it generally does just the opposite. Nevertheless, some scientists continue to ignore these real-world facts, content instead to place their faith in the tenuous output of theoretical climate models (see, for example, our Editorials of 24 Apr 2002 and 1 May 2002).
References
Brichetti, P., Foschi, U.F. and Boano, G. 2000. Does El Niņo affect survival rate of Mediterranean populations of Cory's Shearwater? Waterbirds 23: 147-154.
Elsner, J.B. Bossak, B.H. and Niu, X.F. 2001. Secular changes to the ENSO-U.S. hurricane relationship. Geophysical Research Letters 28: 4123-4126.
Elsner, J.B., Niu, X. and Jagger, T.H. 2004. Detecting shifts in hurricane rates using a Markov Chain Monte Carlo approach. Journal of Climate 17: 2652-2666.
Landsea, C.W, Bell, G.D., Gray, W.M. and Goldenberg, S.B. 1998. The extremely active 1995 Atlantic hurricane season: environmental conditions and verification of seasonal forecasts. Monthly Weather Review 126: 1174-1193.
Lyons, S.W. 2004. U.S. tropical cyclone landfall variability: 1950-2002. Weather and Forecasting 19: 473-480.
Muller, R.A. and Stone, G.W. 2001. A climatology of tropical storm and hurricane strikes to enhance vulnerability prediction for the southeast U.S. coast. Journal of Coastal Research 17: 949-956.
Pielke Jr., R.A. and Landsea, C.N. 1999. La Niņa, El Niņo, and Atlantic hurricane damages in the United States. Bulletin of the American Meteorological Society 80: 2027-2033.
Wilson, R.M. 1999. Statistical aspects of major (intense) hurricanes in the Atlantic basin during the past 49 hurricane seasons (1950-1998): Implications for the current season. Geophysical Research Letters 26: 2957-2960.