Meteorologists have warned that this year's El Nino weather system may have arrived early and could at least match the century's worst, which blighted crops in Indonesia, Australia, the Philippines and southern Africa after a blistering drought in 1982-83.

NASA satellites have found that sea-surface temperatures are up 5C along the Peruvian coast. Concern over the 1997-98 Nino has already driven up tea, coffee and cocoa prices, as the end-of-year rains in east Africa and the monsoons in India and Sri Lanka are tamed by its effects.

El Nino's chief victims are some of the poorer countries of South America, especially Peru. For most of the year, Peru's coast is washed by cold, nutrient-rich waters that sustain a massive fish population. It has been a regular occurrence for these cool waters to be replaced by warmer ones around Christmas, slightly reducing fish stocks, but exceptionally warm currents materialise every two to seven years in the southern Pacific and can remain for months or years at a time. Ninos kill much of the regional fish population and threaten storms, droughts and high winds around the world.

The mechanics of El Nino are well understood, though its origin is still a mystery. Normally, the Pacific is fanned by the constant breath of the trade winds, east-to-west breezes that push warm surface water away from the ocean's eastern side - off Peru and Chile - creating a surge of warmer water along the coasts of Australia and the Philippines.

Off the eastern Pacific coastlines cold water wells up from the Antarctic Humboldt current to replace this surge, like a huge conveyor belt, carrying nitrate and phosphate nutrients, which feed the plankton and hence the fish.

If the winds slacken briefly, warm water begins to slosh back across the Pacific, slowing the upwelling of the Humboldt current.

The warmer the eastern ocean gets, the warmer and lighter the air above it becomes. This reduces the difference in pressure across the ocean. Since the difference in pressure makes the trade winds blow, the easterly winds weaken further, letting the warm water continue its eastward advance.

This reverses the South Pacific's weather system, shifting it 6,000 km to the east. The tropical rainstorms that usually drench Indonesia, the Philippines, India, Thailand and northern Australia are shifted eastwards so that Colombia, Peru and Chile get a soaking.

The last big Nino in 1982-83 - the worst this century - cost some £9 billion in lost livelihood worldwide. It had catastrophic results for Peru; GDP plunged by 12 per cent, agricultural output fell by 8.5 per cent and production in the economically vital fishing industry fell by 40 per cent. The 1997-98 Nino threatens to be at least as destructive.

In Australia, there are fears that Victoria is headed for another "Ash Wednesday"-type bush fire catastrophe if the Nino persists. The Australian Wheat Board warns that serious consequences are feared if the weather pattern does not turn around soon. In the Philippines, the 1982-83 drought destroyed 590,000 tonnes of unmilled rice and devastated 170,000 tonnes of corn. With the 1997-98 drought a foregone conclusion, agriculture experts predict rice harvests will drop by 15 per cent in the first half of 1998. Damage to corn crops in Latin America and sub-Saharan Africa could reduce world supplies by 10 million tonnes, 1.5 per cent of world consumption.

In Indonesia, the Robusta coffee bean harvest is expected to be 25 per cent below normal. In Thailand, the sugar cane crop will be badly affected. The catch of fish along Colombia's Pacific coast is expected to be 20 per cent below normal.

Reservoirs in Colombia are currently down by a fifth, increasing the risks of malaria and cholera.

Named after Jesus, El Nino, "the Christ Child", shows scant mercy.