The report, by the United Nations Food and Agriculture Organisation (FAO), which monitors the world's harvest, warns of "serious consequences" for the world's poorest people from the climatic disruption which is expected to peak early next year. Crop yields are expected to be down across the globe, particularly in Southern Africa, Latin America, Indonesia and Australia.
The El Nino disruption - caused by a warm Pacific current - periodically causes chaos in the world's weather, but this one is shaping up to be the worst ever recorded, and its effects are reverberating around the globe. Damage to harvests, which seems inevitable, would come at a time when stockpiles are low. Every year only just enough food is produced. Buffer stocks of grain have for three years been below what the FAO judges "the minimum necessary for world food security".
This year's harvest is again expected to squeak by, leaving nothing to build up stocks. But the FAO warns that "adverse weather", including the effects of El Nino, may yet cut it back.
According to the agency, drought has already cut the Australian wheat crop by a third. The barley harvest is expected to suffer even more, and exports of both crops are likely to fall. Meanwhile, the dry season has started unusually early in central America, and is especially hot, so fewer crops have been planted, and those already in the ground are stunted. The maize harvest is down by 15 per cent in El Salvador, and maize, sorghum and bean crops have been devastated by drought and heat in parts of Honduras. Guatemala, Nicaragua and the Dominican Republic have also been hit.
While central America bakes in unaccustomed heat, heavy rains have reduced harvests in Bolivia and Ecuador, and there has been flooding in Venezuela. Some scientists believe that the drought in North Korea, which has caused widespread famine, is linked to El Nino.
But the real worry is what will happen next year, when the disruption - due to peak between December and March - should be at its height. The FAO is warning against "a serious impact on the 1998 harvests".
Peru, Bolivia and Ecuador have declared states of emergency in anticipation of disaster, and the central American coffee crop, which will be at a critical flowering stage when El Nino is likely to be at its worst, is expected to be badly affected. World coffee prices have already soared on the potential threats to supplies.
Southern Africa, where harvests are slightly down this year, is likely to be hit by severe drought: earlier this month South Africa's Agriculture Minister, Derek Hanekom, said that the onset of El Nino could halve his country's corn crop next year, costing more than $213m (pounds 133m) in lost exports. Farmers in the Philippines have been advised to plant fast-growing varieties of rice this autumn in the hope of getting in their harvests before disaster strikes. Australia, South America, Indonesia and Thailand are also expected to be in trouble and there arefears that the American Midwest, the world's grain basket, may be affected.
The FAO warns that "even a small reduction" in harvests would lead to "sharp price rises", plunging the world's poorest countries into crisis, as they are unable to buy enough food.