STERKFONTEIN CAVES, South Africa: Climate change in Africa gave rise to modern humans.

Now experts fear that global warming linked to carbon emissions will have its worst impact on humanity's cradle.

"Africa is the most vulnerable continent to climate change," said Jennifer Morgan, director of the Global Climate Change Programme at conservation group World Wildlife Fund (WWF).

"Most African livelihoods depend on rain-based agriculture so droughts and floods will have a serious impact on the workforce," she said, adding that the continent's extreme poverty reduced its ability to cope. Africa's plight will be high on the agenda of a Scottish summit of the Group of Eight (G8) industrialized nations next month which could herald increased aid flows to the region.

British Prime Minister Tony Blair has also made climate change a priority of Britain's year-long presidency of the G8.

Global warming is widely blamed on emissions of heat-trapping gases from cars, factories and power plants gases mostly spewed from the world's richest nations.

"If leaders don't deal with climate change effectively they won't be doing all they can for Africa," said Morgan.

Apocalypse now

Climate change in Africa prodded mankind's distant ancestors along their evolutionary path as forests gave way to grasslands, forcing early humans into an open environment where it appears stone tools and long strides first developed.

But while most past changes in weather patterns were gradual giving our pre-historic ancestors a chance to adapt the pace of global warming today could overwhelm modern Africa.

The United Nations projects that temperatures may rise by 1.4 - 5.8 C by the year 2100.

Desertification threatens to drive millions of Africans from their homes, said a recent international report drawing on the work of 1,360 scientists in 95 nations.

The problem is illustrated by gullies of eroded, barren earth scarring the shoreline of Lake Victoria, which borders Kenya, Uganda and Tanzania. The Kenya-based World Agroforestry Centre says one of them, the Katuk-Odeyo gully, now extends to a remarkable 45 kilometres.

Global warming may already be a source of violence in central Nigeria, where nomadic cattle herders and peasant farmers have been locked in conflict over scarce land for decades as the desert creeps southwards.

Deforestation, dwindling water supplies and rising sea levels could spark mass migrations.

"Regions that are already least secure in food production, like sub-Saharan Africa, stand to be worst affected by global warming as wet areas become wetter and dry areas become drier," says a recent global report on climate change.

Uganda's climate has become hotter and its rains more erratic in the last decade, researchers and the government say, posing a threat to its key coffee crop.

Rising sea temperatures are also among the threats seen to the coral reefs off Africa's lush east coast, the life-blood of poor coastal communities dependent upon fisheries and tourism.

Humanity's cradle

And this tragedy of the weather is unfolding across the continent where climate change gave birth to modern humans.

The evidence for this is embedded in the Sterkfontein caves, 30 kilometres northwest of Johannesburg, where hominid fossils dating back over 4 million years have been unearthed.

"There was a drying up of Africa around 2.5 million years ago... There was a change from forest to grasslands," said Doctor Ron Clarke, who heads excavations at Sterkfontein.

Intriguingly, it was in this period that the Sterkfontein fossil record reveals our ancestors first making stone tools.