The long-range forecasters are in a tizzy. Observations of the temperature of the surface of the sea off the coasts of Peru and Ecuador in recent months have shown it to be rising steadily, so that it is now 2 C to 3C above the normal values. This, it seems, can only mean one thing: El Nino must be coming back.
The term El Nino is used to describe a general warming of the surface waters of large areas of the Pacific Ocean which occurs at irregular intervals of between three and seven years. In normal times, steady easterly trade winds in the equatorial Pacific literally drag the warm surface water with them to the west, causing a rise in sea level in the western Pacific. At the same time, cold water from below wells up in the eastern part of the ocean near the coast of South America. It is when the trade winds relax - as they do periodically as a prelude to El Nino - that the warm surface waters in the western Pacific slosh back eastwards to raise the temperature near Peru and Ecuador.
Warmer water over the vast expanse of the tropical Pacific makes a great amount of extra energy available to the air in contact with it, so the periodic heart-beat of El Nino causes oscillations in the world's climate. At its peak, normally arid areas of western South America are drenched with rain, and other areas in the low latitudes in which rain is normally abundant, experience droughts.
Scientists were reasonably sure some years ago, after predicting the events of 1987 and 1991, that their computer models had unravelled nearly all the mysteries of El Nino. But when the 1991 El Nino persisted for an unprecedented three years, rather than the usual nine months or so, they began to wonder if something unusual might be happening to our global climate. Their fears will be further compounded by this early arrival of yet another El Nino, completely unexpected and several years ahead of schedule.
But it is not just El Nino's premature arrival of that is worrying; it is also its apparent strength. The observed increases in sea surface temperature are similar to those observed in 1957 and 1972 - both years in which an El Nino brought extreme conditions to many countries on the equatorial Pacific rim. This has led the American NASA weather forecasters to predict that Indonesia, India, Australia and East Africa are likely to be drier than normal in the coming months, while a very wet winter, they say, can be expected in central Chile, Uruguay and parts of Argentina.