It has contributed least to climate change, the experts say, and is least prepared for the consequences, but could mitigate some of the worst effects through cross-border cooperation.

"African governments are not doing enough," said Anthony Nyong, the Nigerian coordinating lead author of the Africa chapter in the UN's latest Intergovernmental Panel on Climate Change (IPCC) report, which was released on Friday in Belgium.

"It is better to face the precipice than park an ambulance at the bottom of the valley," he told a news conference.

"These threats do not respect national boundaries, and we will not stop screaming about this until governments take it on board ... We must go regional and look at what effects us all."

The IPCC report, prepared by 2,500 scientists, was the starkest warning yet of the impact of climate change in Africa.

Under current forecasts, as many as 1.8 billion Africans will not have enough water by 2080, crop revenues could fall by as much as 90 percent by the end of the century and deadly diseases like malaria could spread to currently safe highlands.

HOPE AND PLANNING

Millions of Africans will be threatened by coastal flooding and more than a quarter of wildlife habitats will be at risk.

UN experts say sparse historical data for Africa, coupled with inadequate forecasting centres, were adding to problems.

Another lead author of the chapter, Andrew Githeko, said Kenya's experience with diseases like Rift Valley Fever -- which killed more than 100 people earlier this year -- showed how much the continent had to gain from improving forecasting data.

He worked for a Kenyan government unit studying climatic effects on public health. When meteorologists were able to issue advance warnings of risks, it found, they could often be contained at a fraction of the cost.

Preventing malaria cost around US$2.50 per case if action was taken ahead of an outbreak, Githeko said, but that rose to US$30 if no action was taken and patients were treated in hospital. Kenya had lost about US$5 million by failing to vaccinate in time against its 10-week epidemic of Rift Valley Fever, he said.