Ten years or so ago, I attended a seminar where a distinguished climatologist was virtually hooted by the audience for his discussion of the then-obscure El Niño phenomenon.

Little more than witchcraft or black magic, the scoffers said of the observation by South American fishermen that cyclically abnormal water temperatures around Christmastime heralded adverse weather patterns.

Now, El Niño is an established fact. Some can be severe, with major winter storms in the western United States, heavy rains and snow elsewhere, drought in other areas, colder winters in some areas, warmer winters in others.

Other El Niños — including the current one now in the process of winding down — are more moderate.

As computer power has increased and weather data generation has become more extensive and sophisticated, climatologists are refining their knowledge of the El Niños, which are birthed when (for reasons unknown) sea surface temperatures in a section of the tropical Pacific Ocean become slightly warmer than normal. This sets up a global circulation pattern that moves the warmer water eastward, in the process changing jet stream patterns that affect U.S. winters and weather elsewhere in the world.

The 2002-03 El Niño has had varied effects around the globe, according to Chester Ropelewski, director of monitoring and dissemination at the International Research Institute for Climate Prediction at Columbia University, who spoke at Agricultural Outlook Forum 2003 at Washington, D.C.

India had its first major monsoon failure since 1987 and the driest July on record; southeast South America had a prolonged wet spell (photos were circulated of people fishing in wheat fields); drought in Australia saw rainfall in the lowest 5 percent to 10 percent amounts in history (causing, among other things, severe cotton yield losses).

Despite its devastation in some areas of the world, this El Niño, was “kind of in the middle of the pack, a moderate episode,” and “not a big deal elsewhere,” Ropelewski says. Current indications are that “it is dying more quickly than we thought, and is expected to be over by late in the Northern Hemisphere spring.”

While some of this winter's extremes in the United States have been attributable to the El Niño, other factors such as the “Arctic Oscillation” have been a stronger influence in the colder-than-normal temperatures in the northeast states, says Jim Laver of the National Weather Service's Climate Prediction Center. But it has had “some of the classic impacts,” including more storms and precipitation across California, a milder-than-normal winter across the northern states and western Canada, and drier-than-normal conditions in the Dakotas and along the Canadian border. “We believe it played a role in the big snowstorm in the Northeast, but we had no way of knowing it would be a super-cold winter.”

Defining the El Niño phenomenon in terms of weather impact is “a work in progress,” Laver says. And says Gail Martell, president of martelcropprojections.com, because El Niño projections don't always hold true, “it's hazardous to make crop production estimates based on ‘typical’ El Niño weather — especially in the Southern Hemisphere, where mid-summer weather changes can reverse crop potential.”

e-mail: hbrandon@primediabusiness.com