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Our Affair with El Nino

Natural History, July-August, 2004 by Laurence A. Marschall

Our Affair with El Nino by S. George Philander Princeton University Press, 2004; $26.95

For centuries, residents of Peru's and coast have welcomed a warming of the normally frigid offshore waters, which comes every few years at Christmastime. They called it El Nino, Spanish for the baby Jesus. Fishermen still look to El Nino's arrival as a temporary respite from their work; most of their edible catch thrives best in colder waters. But when the waters of El Nino are particularly warm and linger longer than usual, the effects on local climate can be memorable. "The desert becomes a garden," recalled a visitor in 1891. "The soil is soaked by the heavy downpour, and within a few weeks the whole country is covered by abundant pasture." Residents have reported armies of yellow-and-black water snakes floating in balmy swells, along with bobbing armadas of bananas and coconuts.

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These mysterious effects hinted that El Nino was somehow connected with events far from the shores of Peru, and that, indeed, turned out to be the case. During the International Geophysical Year (actually an eighteen-month period from July 1957 until December 1958), a worldwide collaboration to collect data on the state of the planet, oceanographers first recognized the phenomenon for what it was: Peru's El Nino was just the easternmost edge of a strip of unusually warm water that periodically overspread the equatorial Pacific. What's more, they discovered, El Nino has a sister phenomenon, La Nina, a period of unusually cold waters that seemed to alternate with El Nino.

At the same time, meteorologists recognized characteristic shifts in the patterns of prevailing winds accompanying the seasonal temperature changes. Within a few decades El Nino's influence had been linked to a wide variety of weather and climate changes thousands of miles from its origin: the arrival of monsoons in India, the severity of winters in the United States, the intensity of droughts in southern Africa. Today scores of buoys continuously monitor wind and water conditions across the Pacific, updating El Nino's vital signs (check out www.pmel.noaa.gov/toga-tao).

There's a danger, though, warns S. George Philander, a geoscientist at Princeton University: all the supposed linkages can get pushed too far. In the popular mind El Nino has become the whipping boy for any change in climate that seems out of the ordinary.

The real phenomena, Philander explains, are far more complex. As elaborate as computer models of climate are today, they can only begin to approximate how water temperatures affect winds, how winds affect ocean currents, how increasing carbon dioxide alters baseline ocean temperatures, and how a host of other factors combine. Climatologists are only beginning to turn today's weather data into a reliable guide to the climate of the future.

El Nino is not just an oceanographic and meteorological curiosity. It has also come to prominence at the right time for focusing attention on the complexities of global climate. Environmental science and policy will turn to El Nino both as a starting point for research and as an object lesson on the connectedness of nature.

LAURENCE A. MARSCHALL, author of The Supernova Story, is the W.K.T. Sahm professor of physics at Gettysburg College in Pennsylvania, and director of Project CLEA, which produces widely used simulation software for education in astronomy.

Our Affair with El Nino

Natural History, July-August, 2004 by Laurence A. Marschall

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