83rd Annual

Tuesday, 11 February 2003: 1:30 PM
Who Discovered the El Niño-Southern Oscillation?
Gregory T. Cushman, Southwestern University, Georgetown, TX
Two giants of 20th-century meteorology, Gilbert Walker and Jacob Bjerknes, are usually given credit for discovering the El Niño-Southern Oscillation phenomenon. During the early 1920s, Walker empirically identified a periodic variation in atmospheric pressure over the Indo-Pacific which he christened the "Southern Oscillation." During the 1960s, Bjerknes posited a physical mechanism to explain the atmospheric features of this phenomenon over the equatorial Pacific which he christened the "Walker Circulation." Both men deserve recognition since they opened the way for our present understanding of the global climate system.

But meteorology consists of more than brute number crunching and elegant physical reasoning. These two giants should share credit with others who identified important features of this phenomenon--none of whom were meteorologists. Three Americans: Robert Cushman Murphy, T. Wayland Vaughan, and Milner Bailey Schaefer deserve recognition for organizing a trans-Pacific network of interested scientists in the late 1920s and late 1950s. Schaefer, in fact, paid Bjerknes to study the "El Niño" problem in order to predict variations in Pacific tuna distribution. Three German oceanographers: Gerhard Schott, Erwin Schweigger, and Klaus Wyrtki deserve recognition for interpreting oceanic features of this phenomenon.

Credit for any scientific discovery automatically entails a subjective value judgment of what counts as new understanding. The basis for such judgments changes over time. Some scientists deserve credit for "discovering" the El Niño-Southern Oscillation, even though they were motivated by beliefs we now consider wrong-headed.

In 1877, the Chilean Benjamín Vicuña MacKenna immediately recognized the link between climate anomalies all over the Pacific basin--because they corresponded with a powerful tsunami. During the early 1890s, two Peruvian scientists used "rustic astronomy" to interpret anomalies along the arid Peruvian coast. Using information from local fisherfolk, Camilo Carrillo adopted the term "El Niño countercurrent"--the origin of our name for a much larger phenomenon--to describe periodic variations in the Humboldt (Peru) Current. Víctor Eguiguren compiled a rough chronology of rainy seasons in northern Peru to prove this region was becoming wetter over time. Beginning in the 1920s, the Dutch-colonial scientist H. P. Berlage, Jr. turned Walker's Southern Oscillation into a usable, potentially predictive concept. He may have been the first to recognize its direct connection with oceanic features off the coast of Peru. His contribution is often discounted, however, because it was intended to bolster the discarded theory that most interannual atmospheric variation is tied to solar cycles.

The work of these four men is important to scientists working today for another reason. William H. Quinn fundamentally based his famous chronology of the El Niño-Southern Oscillation on their work. Despite his best efforts, Quinn's chronology contains artifacts of the discarded theories these scientists were trying to prove. Historians of science can thus provide a major service to working climatologists, not by deciding which scientists deserve the most credit for a discovery, but by showing how the values of climatologists have changed over time and how this change has itself influenced our current understanding.

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