"There is strong evidence that global climate is changing and that the social and economic costs of slowing down global warming and of responding to its impacts will be considerable," said the report by FAO's Committee on World Food Security.

Many scientists fear rising temperatures, blamed mainly on heat-trapping gases from burning fossil fuels, will melt ice caps, raise sea levels by almost a metre (three feet) by the end of this century and bring more floods, droughts and storms.

Global warming would increase the amount of land classified as being either arid or insufficiently moist in the developing world.

In Africa the amount of this type of harsh land could increase by as much as 90 million hectares by 2008, an area nearly four times the size of Britain.

Changes in temperature, rainfall as well as an increase in the number of so-called "extreme weather events" such as floods will bring with them potentially devastating effects.

The world suffered 600 floods in the past two and a half years, which claimed the lives of about 19,000 people and caused $25 billion in damages, excluding December's devastating tsunami in southeast Asia that killed more than 180,000.

FAO said scientific studies showed that global warming would lead to an 11 percent decrease in rain-fed land in developing countries and in turn a serious decline in cereal production.

"Sixty-five developing countries, representing more than half of the developing world's total population in 1995, will lose about 280 million tons of potential cereal production as a result of climate change," FAO said.

The effect of climate change on agriculture could increase the number of people at risk of hunger, particularly in countries already saddled with low economic growth and high malnourishment levels.