Lord May of Oxford, the president of the Royal Society, said the cost of dealing with the adverse effects of climate change could soak up all the aid to African countries.
In an open letter to G8 environment ministers who are to meet in London on 1 November, Lord May warns that the Gleneagles agreement on aid and debt relief to Africa could amount to nothing.
"As long as greenhouse gas concentrations continue to rise, there is the very real prospect that the increase in aid agreed at Gleneagles will be entirely consumed by the mounting cost of dealing with the added burden of adverse effects of climate change in Africa," Lord May said.
"In effect, the Gleneagles communiqué gave hope to Africa with one hand, through a promise of more aid but took that hope away with the other hand through its failure to address adequately the threat of climate change," he said.
At the Gleneagles summit in July, G8 leaders agreed on a package of measures to help to lift Africa out of poverty but kept that separate from an action plan on climate change.
"But the action plan on climate change fell far short of a strategy to stop the rise in greenhouse gas levels in the atmosphere," he added.
At the Gleneagles summit, President George Bush, an arch-sceptic of global warming, did not want climate change to be connected with aid to Africa and managed to separate it from the joint communiqué.
However, Lord May, a former chief scientific adviser to the Government, warned that there is mounting scientific evidence to show that global warming is the biggest single threat to the world today - especially developing countries.
The latest study, published today ,reveals for instance that the rise in man-made greenhouse gases may already be responsible for an increase in drought conditions and risk of famine in eastern Africa.
Lord May cites the results of research by James Verdin of the US Geological Survey who found that rainfall has decreased steadily since 1996 in Ethiopia and neighbouring countries which coincides with a corresponding increase in surface-water temperatures in the southern Indian Ocean.
"The researchers point out that this reduction in rainfall is adversely affecting the growth of crops and increasing the number of people who require food aid," Lord May said.
"This finding has particular resonance, coming as it does 20 years after a severe famine in Ethiopia attracted worldwide attention through Live Aid and other events that pricked the collective conscience of richer developed countries," he added.
"In short, the scientific evidence now presents a more compelling case than ever before for tackling the threat from climate change by stopping the rise of greenhouse gas levels in the atmosphere."
Richer countries have a responsibility to do something about climate change by stabilising the rise in greenhouse gas emissions that they are primarily responsible for, he said.
"Therefore, if the increase in aid and other measures outlined in the Gleneagles action plan on Africa are to create the maximum benefit, they must be accompanied by effective action on climate change by stopping the inexorable rise in greenhouse gas levels in the atmosphere," Lord May said.
A major failing in the communiqué was that it did not acknowledge the importance of securing an agreement on stabilising levels of carbon dioxide in the atmosphere.
Lord May warns G8 environment ministers that without a definition of target concentrations of greenhouse gases, discussions about national emissions targets are nothing more than an academic dispute.