For most of the year, Peru's coast is washed by cold, nutrient-rich waters that sustain a mighty fish population. It has been a regular occurrence for these cool waters to be replaced by warmer ones around Christmas, slightly reducing the fish population. Scientists do not know why this phenomenon, El Nino - Spanish for the baby Jesus - develops. But the term has come now to describe a more sinister occurrence - exceptionally warm currents that remain in the Southern Pacific for months or years at a time, occurring every two to seven years, decimating the regional fish population and threatening storms, droughts and high winds around the world.
El Nino coincides with heavy rains in Peru and in the southern United States, with droughts hitting Brazil and eastern Australia; and normal weather patterns becoming more unpre- dictable around the world.
The mechanics of El Nino are understood, though the cause is a mystery. Trade winds blow across the Pacific Ocean from east to west, creating a piling-up effect of water on the coasts of Australia and the Philippines. Like a huge conveyor belt, the oceans pull cold water up from the deep trenches along the coasts of Peru and Equador. If these winds drop, warm water creeps back across the Pacific and halts the upwelling of cold water. This warmer water brings with it the warm wet weather that would normally hit Indonesia, the Philippines and North Australia, instead leaving those areas in drought, and drenching the western coast of South America - the reversal of the south Pacific's weather.
The knock-on effect across the globe is well documented; abnormal warming on the surface of the central Pacific generates huge volumes of warm, moist air. This disrupts the normal flow of the jet streams. California, Israel and its neighbours record higher rainfall at times of El Nino. Man-made global warming, caused by the build-up of greenhouse gases, may be worsening the effect of El Nino.
Nasa satellites recently measured that sea-surface temperatures in the Pacific have risen this year at a faster rate than ever recorded. Concern over the latest El Nino has already driven up tea prices, as the end-of-year rains in east Africa and the monsoons in India and Sri Lanka are tamed by its effects.
Even if Britain escapes the worst effects this winter, experts predict a rise in the price of coffee, cocoa and sugar as tropical crops suffer from droughts or heavy rains.Reuse content