PRETORIA - Africa will suffer the most if the world fails to reduce global warming, with parts of the impoverished continent becoming uncultivable or uninhabitable, top British government scientists said on Wednesday.

In a presentation in Pretoria, David King, the British government's chief scientific adviser, warned climate change, if unchecked, would lead to worsening drought in Africa as well as flooding along much of its coastline.

He said an additional 70 million Africans could be at risk of hunger by the 2080s as a result of continued global warming -- temperatures in Africa have risen by about 0.7 degrees Celsius during the last century.

"This is the continent that will come under the most severe pressure from climate change," King told academics and media.

Gordon Conway, the chief scientific adviser for Britain's department for international development, said the current trend in Africa's climate was characterised by polarised change. "It's going to get wetter and drier," Conway told the group.

They urged Africa to make climate change a top priority and the international community to do a better job of sharing technology and skills with what they described as a key battleground in the global warming debate.

Britain has taken a leading role in pushing for a global agreement by 2009 to cut carbon dioxide emissions, the so-called greenhouse gases that are the biggest contributor to the warming of the planet.

Although consensus is building on the need for action, the United States, the top emitter, is among those that have expressed reservations about how a global agreement would be implemented.

U.S. President George W. Bush agreed at the Group of Eight summit in June that substantial cuts in greenhouse gas emissions were warranted but stopped short of defining what the United States considered an appropriate reduction.

The European Union, Japan and Canada have all talked about a need to halve world emissions by 2050 to slow warming.

"We have managed to push the point along, but without American leadership it is going to be a struggle," King said.

There is growing support for the "Bali road map," a two-year plan agreed in Indonesia that aims to follow up on the United Nations' Kyoto Protocol, which obliges 35 industrial nations to cut emissions by 5 percent below 1990 levels by 2008-2012.

Among the proposals likely to spark intense debate is one by developing nations with large areas of forest to have wealthy nations that have contributed the most to climate change compensate them for keeping their forests intact.