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 Nino is an established fact. Some can be severe, with major winter storms in the western U.S., heavy rains and snow elsewhere, drought in other areas, colder winters in some areas, warmer winters in others.

Other El Ninos – 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 Ninos, 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 Nino 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 in Arlington.

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 Nino, 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 spring in the Northern Hemisphere.”

While some of this winter’s extremes in the U.S. have been attributable to the El Nino, 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 dryer-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 Nino phenomenon in terms of weather impact is “a work in progress,” Laver says.

And says Gail Martell, president of martelcropprojections.com, because El Nino projections don’t always hold true, “it’s hazardous to make crop production estimates based on ‘typical’ El Nino weather – especially in the Southern Hemisphere, where midsummer weather changes can reverse crop potential.”

Typically, El Nino’s weather extremes are strongest December-February, she notes, but the current warm episode peaked in December and has been declining ever since. As it has weakened, its “signature weather” disappeared and was replaced by opposite weather extremes – changes that were felt simultaneously in widely separated areas of the globe.

“This erratic behavior proves El Nino can’t be used to predict crop production,” Martell says. “In some instances, El Nino created predictable weather; for example, the drought in Indonesia. But it failed the test in the American Great Plains, where serious drought, not wetness, developed this winter.”

El Nino produced “both excellent and poor soybean crops in Argentina,” she says. “What’s surprising is that both bad and good harvests occurred in strong El Nino years. And another conundrum: El Nino winters should be wet in the Great Plains, but instead this winter has been very dry – indeed, the November-January period was one of the driest on record in Kansas, and winter wheat deteriorated badly with the worsening drought.”

e-mail: hbrandon@primediabusiness.com