Starting with the Atmosphere

The first pieces to the El Niño puzzle came from atmospheric studies. In the early part of the twentieth century, British mathematician Sir Gilbert Walker, director general of meteorological observatories in India, took advantage of existing weather data to make a substantial breakthrough in atmospheric science. In 1899 the monsoon rains on which Indian farmers depend failed to come, triggering a devastating famine. Asked to find a way to predict such weather vagaries in the future, Walker began sifting through some 40 years’ worth of temperature, atmospheric pressure, and rainfall data culled from a worldwide network of weather stations. He noticed a kind of seesaw relationship between atmospheric pressure in the eastern South Pacific (east of Tahiti) and the Indian Ocean (west of Darwin, Australia)--that is, if pressure was high in one region, it was usually low in the other and vice versa.

In a 1928 paper presented to the Royal Meteorological Society, Walker named this seesaw pattern the Southern Oscillation and devised a yardstick that measured pressure differences between the two regions. He observed that, when pressure was very high in the east and low in the west, the monsoon rains in India were heavy. When the pressure difference was small, the rains failed and drought often ensued. Moreover, Walker's research showed that drought conditions hit not only Australia, Indonesia, and India but also parts of sub-Saharan Africa, and at the same time there would be mild winters in Canada. Because he had plotted certain time-lag correlations between these pressure differences at different times of the year, Walker also believed the measurements could be used for long-range forecasting for some locations.

Gilbert Thomas Walker. (Photo courtesy of E. M. Rasmussen, University of Maryland)

Despite his insight and vision, Walker was unable to identify the physical processes responsible for the Southern Oscillation, and for the next three decades numerous factors conspired to dampen further research on the phenomenon. Chief among them was that from 1930 to 1950 the climate signals marking the Southern Oscillation and El Niño were much less pronounced than they had been, and interest in the subject dropped off. Then in 1957 a confluence of events in climate, science, and international politics brought a resurgence of interest.

That year the Soviet Union launched Sputnik, the first artificial satellite, spurring a dramatic increase in support for scientific research of all kinds throughout the West. As it happened, the year also ushered in a large El Niño. Although this was a strong event, it might have passed unnoticed, except that 1957 had been designated as an International Geophysical Year, a year when scientists from all countries cooperate to improve existing understanding of the solid Earth, the oceans, and the atmosphere. As a result, scientists around the world were conducting intensive measurements of the planet. Among the data they gathered were not only atmospheric measurements but also sea surface temperatures throughout the Pacific--information that had not been available in Gilbert Walker's time. Some researchers in the 1950s noted that high sea surface temperatures off the coast of Peru seemed to correlate with a small difference in pressure across the tropical Pacific. Indeed, scientists at the Scripps Institution of Oceanography convened a group of scientists in 1959 to discuss the phenomenon. However, it wasn't until the late 1960s that meteorologist Jacob Bjerknes, of the University of California, Los Angeles, described a mechanism that linked Walker's observations of the Southern Oscillation to El Niño.

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