Disease spread by global warming could kill an extra 185 million people in sub-Saharan Africa by the end of the century, a study by a global charity has found.
In addition the report commissioned by Christian Aid said climate change could turn millions more into refugees unless rich nations take action now.
Commenting on its findings the charity called on rich developed countries to end their dependence on fossil fuels and switch to energy sources such as wind, solar and waves.
Governments must also set aside large sums of aid to help poorer nations to adjust to the worst impact of global warming, it said.
"Rich countries must take responsibility for having largely created this problem - and cut CO2 emissions radically," Christian Aid said in its report entitled The Climate of Poverty: Facts, Fears and Hopes.
"Climate change is taking place and will inevitably continue. Poor people will take the brunt, so we are calling on rich countries to help them adjust as the seas rise, the deserts expand, and floods and hurricanes become more frequent and intense."
Most scientists agree that global warming is due to burning fossil fuels for transport and power, and new calculations suggest that having risen by 0.6 degrees Celsius in the 20th century, global temperatures could surge three degrees by 2100.
Melting ice caps
Christian Aid said it based its estimate of 185 million deaths due to disease on figures from the UN and the Inter-governmental Panel on Climate Change. Global warming would allow carriers, including mosquitoes, to expand their ranges.
Melting ice caps and glaciers are eroding coastlines at a rapid rate, raising sea levels and reducing reliable sources of fresh water.
"Poor people will take the brunt, so we are calling on rich countries to help them adjust as the seas rise, the deserts expand, and floods and hurricanes become more frequent and intense"
At the same time, changing weather patterns were increasing the incidence of floods and droughts, with arid regions becoming drier and wet regions getting wetter.
These changes would increase tensions as resources - water and fertile land - became more scarce, the religious charity said, noting the farmers in northern Kenya were fighting over a diminishing number of waterholes to feed their cattle.
"The unfolding disaster in east Africa, where 11 million people have been put at risk of hunger by years of unprecedented drought, is a foretaste of what is to come," the report said.
"In this sense, the environment is too important to be left to the environmentalists," Christian Aid said, declaring that it was switching its campaign goals to focus on the four great effects of global warming - pestilence, floods, famine and war.
The Kyoto Protocol is the only global vehicle for cutting carbon emissions, but it expires in 2012.
The world's worst polluter, the US, rejects it and it does not commit the major developing nations to make any reductions.
As talks get under way to try to find a successor to Kyoto and encourage the US to sign up, Christian Aid said developed nations had to cut carbon dioxide emissions by two-thirds by 2050, and major developing nations India, Brazil and China also had to agree to set tough targets for themselves.