Discover, January 31, 1995
Every few years the people of Peru endure a trial. Normally the trade winds blow west across the Pacific, pushing warm surface water toward the Philippines. That allows cool water to well up from the ocean depths off the coast of South America, bringing nutrients that support the Peruvian fishery. But every few years the trade winds collapse, and the warm water sloshes back east in a vast, slow wave that caps the supply of cold water and crushes fish populations. Because it often happens around Christmas, the disturbance has been dubbed El Nino–the Little One, in reference to the infant Jesus–but over the past 15 years researchers have discovered just how inapt that name is.
El Nino alters weather patterns so drastically that it can simultaneously cause droughts in Indonesia and floods in California. There is a silver lining to the storm clouds, though, one that was dramatized by two reports in 1994: to the extent that our weather is controlled by this global machine, it may be more predictable than was thought.
Researchers used to think that at worst an El Nino lasted three years. But Gregg Jacobs and his co-workers at the Naval Research Laboratory at the Stennis Space Center in Mississippi reported this past August that the wave of warm water from the 1982 El Nino, the most powerful one this century, survived for 12 years. Measuring only eight inches high and moving about five miles an hour, the wave is not something you’d notice from a ship; Jacobs and company tracked it on a computer simulation and through satellite measurements of sea levels.
They watched it reach South America in two months and then spread along the coast, raising sea levels as far away as Alaska. Then, like a wave reaching the end of a bathtub, it began to roll slowly back west–all the way back across the Pacific. In 1991 the wave encountered the powerful current of warm water that flows from Japan eastward, known as the Kurishio extension, which is something like the Gulf Stream of the Pacific. Nine years after it was created, the El Nino wave was still powerful enough to push part of the current 200 miles north. There have been two more El Ninos since 1982, but that one is only now fading away in the Bering Sea.
El Nino’s tendrils reach outside the Pacific; through an atmospheric domino effect, the shift in Pacific winds forces shifts in winds and rainfall patterns around the world. Not long ago agricultural experts and El Nino researchers met in Budapest to discuss how it might also be affecting harvests. When Roger Buckland, of the Southern African Development Community (a group of ten governments in the region), showed his records of corn harvests from 1970 to 1993 in Zimbabwe, oceanographer Mark Cane was stunned. Cane, who works at the Lamont-Doherty Earth Observatory in Palisades, New York, saw that Buckland’s sawtooth graph beautifully matched the rise and fall of sea-surface temperatures in the Pacific.
Surprisingly, the link between El Nino and rainfall in Zimbabwe was not nearly as strong–which is probably why no one had noticed the extraordinary connection to the corn harvest. It appears that El Nino must affect other factors, like temperature or perhaps even rodent populations, that also affect corn. In any case, the link to corn was so tight, Cane and Buckland reported last July, that they could accurately (although retrospectively) predict Zimbabwean harvests for the last 20 years using El Nino data for the previous year. “We were wrong for only one year out of 20,” says Cane.
Cane can now forecast the 1995 harvest in Zimbabwe: farmers there should expect normal or slightly lower than normal yields. And while no one can yet do the same for Iowa, Jacobs’s work may help researchers understand how El Nino influences long-term weather across the North Pacific and over North America. Both bits of research suggest, in other words, that though El Nino is a giant, it may not be an unpredictable one. That bodes well for our attempts to live with it.
Copyright 1995 Discover Magazine. Reprinted with permission.