The Christian Aid charity has warned that 184 million people in Africa alone could die as a result of climate change before the end of the century.
Christian Aid has demanded greater carbon dioxide emission cuts
Climate-induced floods, famine, drought and conflict could reverse recent gains in reducing poverty, it says.
Its report says rich nations must aid poorer ones to adopt non-fossil-fuel energy sources such as solar power.
The report comes as almost 190 states gather in Bonn, Germany, to discuss climate change.
The Christian Aid report, entitled The Climate of Poverty: Facts, Fears and Hopes, says rich countries must end their dependence on fossil fuels and aid poorer nations to switch to wind, solar and wave energies.
"Climate change is taking place and will inevitably continue," the report says.
"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."
The author of the report, John McGhie, said that for $50bn (£26bn) the whole of sub-Saharan Africa could be turned into a solar-generated economy.
"And $50bn is exactly the same amount as actually the continent would have to pay on extra fuel bills from oil," he said.
The report argues that economic growth can be stimulated through localised renewable energy.
However, critics argue developing countries should be left to concentrate on economic growth in whichever way they see fit.
Although scientists are divided on the impact of global warming, recent calculations suggest global temperatures could rise by three degrees by 2100.
Droughts, floods and infestations could increase, the report says
Christian Aid says effects such as increased floods and droughts and a growth in areas infested by malaria-carrying mosquitoes could cause a huge rise in deaths.
The Kyoto Protocol on cutting carbon dioxide emissions, believed to be the key cause of global warming, expires in 2012 and does not require major developing nations to make reductions. In addition, the US has rejected it.
Christian Aid said developed nations must cut carbon dioxide emissions by two-thirds by 2050.
At the two-day dialogue on climate change in Bonn, developing nations are expected to urge richer countries to take a greater lead.
The poorer countries say the richer ones are mainly responsible for the situation today.
The Kyoto Protocol's supporter nations are supposed to reduce emissions by an average of 5.2% below 1990 levels by 2008-12.
The Bonn meeting is a precursor to talks from 17-25 May that will begin discussions on how to extend Kyoto to beyond 2012. Those talks could take several years.