Experts say global warming is likely to affect people living in Africa more than on any other continent and warn that African policymakers must begin to prepare for such an event. An international panel of experts on climate change made the projection Tuesday in its latest report. Correspondent Scott Bobb reports from Johannesburg.

The Intergovernmental Panel on Climate Change, IPCC, says global warming could upset the livelihood of as many as 250 million Africans in the next 13 years by reducing access to water and food, degrading forests, mangroves and coral reefs and causing large migrations of people.

One of the main authors of the report, Guy Midgley, says at the same time Africa is among the regions least able to address such a crisis.

"It's a continent which is most vulnerable to climate change because of its low adaptive capacity," he said. "You have fairly weak institutional control and inputs and at the same time high levels of projected climate impact. Put those two things together and you end up with substantial vulnerability."

The IPCC was formed nearly 20 years ago to assess scientific studies on climate change. The latest report was compiled over the past six years by hundreds of authors from 130 countries. It is meant to serve as a tool for policymakers.

Midgley says that research is growing and increasingly in agreement. It shows that surface temperatures on land and sea have risen by one to two degrees in the past 34 years and are already affecting weather and ecosystems around the world.

He says in Africa, fish populations have declined in major lakes and coastal areas. The amount of land available for agriculture is shrinking and growing seasons are shorter. The report projects that crops from rain-fed agriculture in some countries could be reduced by as much as 50 percent by 2020.

At the same time, rising sea levels could threaten coastal and island communities and affect industries such as tourism. The report says some adaptation has already begun but the cost could amount to as much as 10 percent of gross domestic products.

He says a major concern in Africa is that so many people are living at subsistence levels.

"A lot of people in Africa are not living buffered by insurance, buffered by savings, by credit availability," Midgely said. "So when resources become less available people potentially could be quite mobile. And that's always a problem for social security, for unrest, etc."

He notes that in a major irony, warming temperatures may actually boost agriculture and water supplies in temperate zones such as the northern hemisphere.

Last November, then-U.N. Secretary-General Kofi Annan spoke at the opening of the climate change meeting in Nairobi. He said the impact of climate change will fall disproportionately on the world's poorest countries, many of them here in Africa. He added that these people already live on the front lines of pollution, disaster and the degradation of resources and land.