Managing El Nino

Although researchers have improved on their skills to predict extreme climate changes like the El Nio, they still have a long way to go

Published: Monday 31 May 1999

there have been several scientific reports this year in which researchers have stated the lessons learnt from the record-breaking 1997-98 El Nio. Though opinions differ, everyone agrees that climatologists did better than during the last big El Nio in 1982-83. Ants Leemta, director of the us National Weather Service's Climate Prediction Centre, says no one forecasted the 1982-83 event: "We did not know what was happening then and we had no idea about the regional and international impact of El Nio." Fifteen years later, new forecasting techniques enabled meteorologists to predict at the beginning of 1997 that the tropical Pacific was about to heat up after two years in which the water had been slightly cooler than normal, and then to give three to six months warning to consequent weather changes in the most vulnerable parts of the world.

Leetma says forecasters should take credit for their success. "We came out and announced that we thought that this El Nio would be one of the top three events in the century, and we identified regions such as California that would be at particular risk." Others were more modest. Reviewing all the evidence in the journal Science , Michael McPhaden of the us National Oceanic and Atmospheric Administration concluded, "The 1997-98 El Nio event caught the scientific community by surprise." Although several computer models had predicted that the tropical Pacific would become warmer in 1997, "warming in almost every case were much too weak and developed too slowly", Mcphaden said. Once El Nio was underway, the forecasters quickly adjusted their computers to take account of its unexpected severity.

They were then very good at predicting its impact for different parts of the world over the next few months. But just as they had missed El Nio's rapid onset, all the computer models failed to predict the abruptness of its departure in May-June 1998. If they are to do better next time and offer reliable predictions of global weather patterns years ahead, forecasters need to understand better the extremely complex changes in ocean currents and atmospheric circulation that underline the southern oscillation (the technical name for the cycle between El Nio and La Nia).

Successful global forecasting requires not only a computer model of the complex interplay between wind and waves but also an understanding of the way the southern oscillation interacts with other, less obvious climatic cycles in the Pacific ocean and elsewhere. These include the Pacific decadal cycle, which operates north of the equator, and the North Atlantic oscillations.

There is some evidence that the latest El Nio was so strong because several other cycles were close to their peak. But it is unclear whether this was the result of the natural fluctuation, in which case the next El Nio is likely to be weaker, or whether global warming caused by human activity is enhancing the natural cycles, in which case there may be worse to come. What is important is that scientists are beginning to realise that the long-term climatic fluctuations, as opposed to specific weather systems, are not entirely random and unpredictable.

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