There are three basic claims made by climate alarmists regarding the influence of CO2-induced global warming on ENSO events: (1) that global warming will increase the frequency of ENSO events, (2) that global warming will increase the intensity of ENSO events, and (3) that weather-related disasters are exacerbated under El Niņo conditions. In this summary, we examine the validity of these assertions, beginning with the last of the three claims.
The impacts of ENSO are many and varied. Regionally, each ENSO brings a mix of positive and negative impacts. For the United States, Changnon (1999) estimates that weather events attributable to the El Niņo episode of 1997-98 negatively impacted the economy to the tune of 4.5 billion dollars and contributed to the loss of 189 lives. On the other hand, he concludes that El Niņo-related benefits amounted to approximately 19.5 billion dollars, resulting primarily from reduced energy costs, industry sales, and the lack of normal hurricane damage. In addition, he estimates that a total of 850 lives were saved due to the reduced amount of bad winter weather. Thus, the net economic impact of the 1997-98 El Niņo event, according to Changnon, was "surprisingly positive" for the U.S., in contrast to what was often reported in the media and by the climate alarmists, who tend, in his words, "to focus only on the negative outcomes."
Another one of the "surprisingly positive" consequences of El Niņo-influenced weather events is the moderation of Atlantic hurricanes during El Niņos. Wilson (1999), for example, examined Atlantic basin hurricane frequency over the period 1950 to 1998, finding that the probability of having three or more intense hurricanes during a warmer El Niņo year was approximately 14%, while during a cooler non-El Niņo year this figure jumped to 53%. In a separate study of Atlantic basin hurricanes over the period 1925 to 1997, Pielke and Landsea (1999) reported that average hurricane wind speeds during warmer El Niņo years were about six meters per second lower than during cooler La Niņa years. In addition, they reported that hurricane damage during cooler La Niņa years was twice as great as during warmer El Niņo years. These year-to-year variations thus indicate that, if anything, hurricane frequency and intensity - as well as damage - tend to decrease under warmer El Niņo conditions, which is just the opposite of the impression that is typically conveyed to the public.
The other two claims made by the climate alarmists - that the frequency and intensity of ENSO events will increase as a result of global warming - have their roots in climate model predictions. Timmermann et al. (1999), for example, developed a global climate model that, according to them, operates with sufficient resolution to address the issue of whether "human-induced 'greenhouse' warming affects, or will affect, ENSO." And what did they find? They found that "when the model is forced by a realistic future scenario of increasing greenhouse-gas concentrations, more frequent El-Niņo-like conditions and stronger cold events in the tropical Pacific Ocean result." However, this is not what observational data reveal to be the case. The more frequent strong El Niņo activity of the recent past is in actuality no different from a number of other such episodes of prior centuries, when the CO2 content of the air was considerably lower than it is today, as noted by Allan and D'Arrigo (1999), Eltahir and Wang (1999), Brook et al. (1999) and Rittenour et al. (2000), who instead of conducting a modeling exercise to explore the issue turned their attention to the real world and consulted actual data.
Based upon the instrumental temperature record for the period 1876-1996, Allan and D'Arrigo found four persistent El Niņo sequences similar to that of the 1990s. Then, using tree-ring proxy data covering the period 1706 to 1977, they found several other ENSO events of prolonged duration. In fact, there were four or five persistent El Niņo sequences in each of the eighteenth and nineteenth centuries, leading them to conclude there is "no evidence for an enhanced greenhouse influence in the frequency or duration of 'persistent' ENSO event sequences." Likewise, in the study of Brook et al. (1999), calcite and aragonite layers from two stalagmites in a cave in Madagascar were used as proxies for ENSO events, revealing that "the period 1700-50 possibly witnessed the highest frequency of El Niņo events in the last four and a half centuries while the period 1780-1930 was the longest period of consistently high El Niņo occurrences."
The study of Eltahir and Wang (1999) spanned an even greater time period. Utilizing water-level records of the Nile river as a proxy for El Niņo episodes over the past 14 centuries, they found that although the frequency of El Niņo events over the last two decades was high, it was not without precedent, being similar to trends observed near the start of the century as well as levels of activity that were "experienced during the last three centuries of the first millennium." And in a study of a recently revised New England varve chronology derived from proglacial lakes formed during the recession of the Laurentide ice sheet 17,500 to 13,500 years ago, Rittenour et al. (2000) discovered that "the chronology shows a distinct interannual (3 to 5 years) band of enhanced variability suggestive of El Niņo-Southern Oscillation (ENSO) teleconnections into North America during the late Pleistocene, when the Laurentide ice sheet was near its maximum extent during near-peak glacial conditions."
Thus, on the one hand, we have the prediction of the most sophisticated climate model ever developed to deal with the ENSO phenomenon - the Timmermann et al. model - predicting that global warming will bring more frequent El Niņo-like conditions; while on the other hand, we have several real-world observations demonstrating that El-Niņo-like conditions in the latter portion of the 20th century - which is claimed to be the warmest period of the past millennium - are not unprecedented in terms of their frequency or magnitude and are, in fact, not much different from those that occurred during much colder times. This certainly appears to be a classic case of model inability to simulate the real world, a concern that has been expressed by several authors, particularly in regard to ENSO events (Walsh and Pittock, 1998; Fedorov and Philander, 2000).
A more immediate example of the inability of today's most sophisticated climate models to properly describe El Niņo events is provided by the report of Landsea and Knaff (2000), who employed a simple statistical tool to evaluate the skill of twelve state-of-the-art climate models in real-time predictions of the development of the 1997-98 El Niņo. They found that the models exhibited essentially no skill in forecasting this very strong event at lead times ranging from 0 to 8 months. Indeed, they determined that no models were able to anticipate even one-half of the actual amplitude of the El Niņo's peak at a medium range lead-time of 6 to 11 months. Also, they state that "since no models were able to provide useful predictions at the medium and long ranges, there were no models that provided both useful and skillful forecasts for the entirety of the 1997-98 El Niņo" [authors' italics].
These results do not engender confidence that today's state-of-the-art climate models would do any better at predicting what would happen under future conditions of either warming or cooling. And as is clear from the many studies cited above, they don't. In fact, they fail miserably.
References
Allan, R.J. and D'Arrigo, R.D. 1999. "Persistent" ENSO sequences: How unusual was the 1990-1995 El Niņo? The Holocene 9: 101-118.
Brook, G.A., Rafter, M.A., Railsback, L.B., Sheen, S.-W. and Lundberg, J. 1999. A high-resolution proxy record of rainfall and ENSO since AD 1550 from layering in stalagmites from Anjohibe Cave, Madagascar. The Holocene 9: 695-705.
Changnon, S.A. 1999. Impacts of 1997-98 El Niņo-generated weather in the United States. Bulletin of the American Meteorological Society 80: 1819-1827.
Eltahir, E.A.B. and Wang, G. 1999. Nilometers, El Niņo, and climate variability. Geophysical Research Letters 26: 489-492.
Fedorov, A.V. and Philander, S.G. 2000. Is El Niņo changing? Science 288, 1997-2002.
Kerr, R.A. 1998. Models win big in forecasting El Niņo. Science 280: 522-523.
Landsea, C.W. and Knaff, J.A. 2000. How much skill was there in forecasting the very strong 1997-98 El Niņo? Bulletin of the American Meteorological Society 81: 2107-2119.
Pielke, R.A., Jr. 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.
Rittenour, T.M., Brigham-Grette, J. and Mann, M.E. 2000. El Niņo-like climate teleconnections in New England during the late Pleistocene. Science 288: 1039-1042.
Timmermann, A., Oberhuber, J., Bacher, A., Esch, M., Latif, M. and Roeckner, E. 1999. Increased El Niņo frequency in a climate model forced by future greenhouse warming. Nature 398: 694-696.
Walsh, K. and Pittock, A.B. 1998. Potential changes in tropical storms, hurricanes, and extreme rainfall events as a result of climate change. Climatic Change 39: 199-213.
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.