How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

ENSO (Relationship to Extreme Weather) -- Summary
The anti-CO2 crowd typically makes three different claims about the likely influence of potential global warming on El Niņo-Southern Oscillation or ENSO events: (1) global warming will increase the frequency of ENSO events, (2) global warming will increase the intensity of ENSO events, and (3) weather-related disasters will be exacerbated under El Niņo conditions. In this summary, we explore the validity of the last of these three assertions, starting with a review of studies that characterized the state of our knowledge of the matter at the turn of the past century.

Changnon (1999) determined that adverse weather events attributed to the El Niņo of 1997-98 negatively impacted the United States economy to the tune of 4.5 billion dollars and contributed to the loss of 189 lives, which is serious indeed. On the other hand, he determined that El Niņo-related benefits amounted to approximately 19.5 billion dollars -- resulting primarily from reduced energy costs, industry sales, and lack of normal hurricane damage -- and that a total of 850 lives were saved, due to the reduced amount of bad winter weather. Thus, the net impact of the 1997-98 El Niņo on the United States, according to Changnon, was "surprisingly positive," in stark contrast to what was often reported in the media and by climate alarmists, who tended, in his words, "to focus only on the negative outcomes."

Another of the "surprisingly positive" consequences of El Niņos is their tendency to moderate Atlantic hurricane frequencies and intensities. Working with data from 1950 to 1998, Wilson (1999) determined 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 the probability jumped to 53%. Similarly, in a study of tropical storm and hurricane strikes along the southeast coast of the United States over the entire last century, Muller and Stone (2001) determined that "more tropical storm and hurricane events can be anticipated during La Niņa seasons [3.3 per season] and fewer during El Niņo seasons [1.7 per season]." And in yet another study of Atlantic basin hurricanes, this one 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 decline under warmer El Niņo conditions, which is just the opposite of the impression that is typically conveyed to the public by climate alarmists.

Much the same story has filtered out of other parts of the world. In the North Indian Ocean, for example, Singh et al. (2000) studied tropical cyclone data pertaining to the period 1877-1998, finding that tropical cyclone frequency declined there during the months of most severe cyclone formation (November and May), when ENSO was in a warm phase. Similarly, in New Zealand, De Lange and Gibb (2000) studied storm surges recorded by several tide gauges in Tauranga Harbor over the period 1960-1998, finding a considerable decline in both the annual number of such events and their magnitude in the latter (warmer) half of the nearly four-decade-long record, while noting that La Niņa seasons typically experienced more storm surge days than El Niņo seasons. And in Australia, Kuhnel and Coates (2000) found that over the period 1876-1991, yearly fatality event-days due to floods, bushfires and heatwaves were actually greater in cooler La Niņa years than in warmer El Niņo years.

Even tiny-brained birds seemed to know more than climate alarmists about the relative dangers of La Niņa and El Niņo conditions back in the 20th century. In a study of breeding populations of Cory's Shearwaters on the Tremiti Islands of Italy, for example, Brichetti et al. (2000) found that survival rates of the birds during El Niņo years were greater than during La Niņa years, which fact they ultimately attributed to the soothing influence of El Niņo on Atlantic hurricanes.

So what's happened subsequently? Have things stayed pretty much the same, or have they changed?

Just into the start of the new century, Elsner et al. (2001) used data for annual U.S. hurricane numbers that they obtained from the U.S. National Oceanic and Atmospheric Administration, plus data for average sea surface temperature (SST) anomalies for the region bounded by 6°N to 6°S latitude and 90°W to 180°W longitude (called the "cold tongue index" or CTI, which they obtained from the Joint Institute for the Study of the Atmosphere and the Oceans) to see if there was a connection between the number of hurricanes that hit the eastern coast of the United States each year and the presence or absence of El Niņo conditions. Based on data for the period 1901-2000, they found that "when CTI values indicate below normal equatorial SSTs, the probability of a U.S. hurricane increases." Or as they describe the relationship in another place, "the annual count of hurricanes is higher when values of the CTI are lower (La Niņa events)." Thus, the entire past century of real-world hurricane experience indicates that the yearly number of U.S. land-falling hurricanes has generally tended to decrease during El Niņo conditions, as has the overall occurrence of hurricanes in the entire Atlantic basin.

One year later, Schwartz and Schmidlin (2002) examined past issues of Storm Data -- a publication of the U.S. National Weather Service (NWS) -- to compile a blizzard database for the years 1959-2000 for the conterminous United States. Once completed, they performed a series of analyses on the data to determine temporal trends and spatial patters of U.S. blizzards, as well as their relationship to ENSO. Over the 41-year period of their study, they identified 438 blizzards, which yielded an average of 10.7 blizzards per year. Year-to-year blizzard variability was significant, however, with the number of annual blizzards ranging from a low of one in the winter of 1980/81 to a high of twenty-seven during the 1996/97 winter. In addition, a weak but marginally significant relationship with ENSO was noted, with a tendency for two to three more blizzards to occur during La Niņa winters than during El Niņo winters.

Contemporaneously, Hudak and Young (2002) utilized an objective method of identifying fall (Jun-Nov) storms in the southern Beaufort Sea based on a knowledge of surface wind speed over the period 1970-1995; and by these means they found there was considerable year-to-year variation in the number of storms, but no discernable trend. They also observed a small increase in the number of storms during El Niņo vs. La Niņa years; but they reported that "due to the relatively small number of cases, no statistical significance can be associated with this difference." Thus, in a region of the world where climate models predict the effects of CO2-induced global warming should be most evident, the past quarter-century has seen no change in the number of June-November storms.

Also in the same year, Higgins et al. (2002) examined the influence of two important sources of Northern Hemispheric climate variability -- ENSO and the Arctic Oscillation (AO) -- on winter (Jan-Mar) daily temperature extremes throughout the conterminous United States over the 50-year period 1950-1999. This work revealed there was considerable decadal variability in surface air temperatures. Nevertheless, during El Niņo years the number of extreme temperature days was found to decrease by around 10%, while during La Niņa years they increased by around 5%. With respect to the AO, however, there was basically no difference in the number of extreme temperature days between its positive and negative phases.

Three years later, Goddard and Dilley (2005) wrote that the huge reported "cost" of El Niņo events "contributes greatly to misconceptions about the global climate effects and socioeconomic impacts of El Niņo and La Niņa." For one thing, they report that the monetary figures typically bandied about represent a gross estimate of all hydrometeorological impacts worldwide in specific El Niņo years; but they note that "how these losses compare with those during ENSO-neutral periods has not been established," adding that "during El Niņo events, El Niņo is implicitly assumed to be associated with all climate-related losses." Thus, they decided to rectify this less-than-perfect situation with a more rational approach to the subject.

At the end of their many analyses of different types of data, Goddard and Dilley arrived at three major conclusions. First, they concluded that "perturbation to precipitation over land areas is only weakly affected by ENSO extremes," as they found that "the risk of widespread extreme precipitation anomalies during ENSO extremes is comparable to that during neutral conditions," and that "the highest values of integrated rainfall perturbation are not greater during ENSO extremes than during neutral conditions." Second, they found that "the frequency of reported climate-related disasters does not increase during El Niņo/La Niņa years relative to neutral years." And third, they found that seasonal rainfall forecast skill increases "in magnitude and coverage, during ENSO extremes," such that "the prudent use of climate forecasts could mitigate adverse impacts and lead instead to increased beneficial impacts, which could transform years of ENSO extremes into the least costly to life and property," in a radical reversal of the prevailing climate-alarmist view of the subject.

So what are some of the beneficial impacts of ENSO extremes that Goddard and Dilley say could yield a more complete appreciation of the socioeconomic impacts of El Niņo and La Niņa events? One example, in their words, is the well-established fact that "tropical Atlantic hurricanes that threaten the southeastern United States, the Caribbean, and eastern Central America occur less frequently during El Niņo years (Gray, 1984)," while another is that "warmer winter temperatures commonly are observed in the northern United States during El Niņo, leading to less energy use and, therefore, lower energy prices (Chagnon, 1999)."

Considering these several observations in their totality, Goddard and Dilley concluded that "between mitigating adverse climate effects and taking advantage of beneficial ones through the prudent use of climate forecasts, El Niņo and La Niņa years may eventually result in substantially lower socioeconomic losses, globally, than are realized in other years." Yet even in the absence of such actions, their work (and that of many other researchers) reveals that, averaged over the globe, the people of the earth currently have nothing more to fear during extreme ENSO years than they do in ENSO-neutral years.

And that's about where the state of our knowledge of the subject resides today: ENSO events, which climate alarmists wrongly claim are more frequent in times of greater warmth, do not lead to more frequent and more severe extreme weather events.

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.

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.

De Lange, W.P. and Gibb, J.G. 2000. Seasonal, interannual, and decadal variability of storm surges at Tauranga, New Zealand. New Zealand Journal of Marine and Freshwater Research 34: 419-434.

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.

Goddard, L. and Dilley, M. 2005. El Niņo: catastrophe or opportunity. Journal of Climate 18: 651-665.

Gray, W.M. 1984. Atlantic seasonal hurricane frequency. Part I: El Niņo and 30 mb quasi-biennial oscillation influences. Monthly Weather Review 112: 1649-1668.

Higgins, R.W., Leetmaa, A. and Kousky, V.E. 2002. Relationships between climate variability and winter temperature extremes in the United States. Journal of Climate 15: 1555-1572.

Hudak, D.R. and Young, J.M.C. 2002. Storm climatology of the southern Beaufort Sea. Atmosphere-Ocean 40: 145-158.

Kuhnel, I. and Coates, L. 2000. El Niņo-Southern Oscillation: Related probabilities of fatalities from natural perils in Australia. Natural Hazards 22: 117-138.

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.

Schwartz, R.M. and Schmidlin, T.W. 2002. Climatology of blizzards in the conterminous United States, 1959-2000. Journal of Climate 15: 1765-1772.

Singh, O.P., Ali Khan, T.M. and Rahman, M.S. 2000. Changes in the frequency of tropical cyclones over the North Indian Ocean. Meteorology and Atmospheric Physics 75: 11-20.

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.

Last updated 2 December 2009