By Roger Harrabin
BBC News Environment Correspondent
The poorest people in the world in Asia and Africa will be worst hit by climate change, a UK government report says.
More extreme weather events are forecast
It says droughts and floods fuelled partly by carbon emissions from countries such as the UK will hurt the same people targeted by overseas aid.
The report was obtained by BBC News under the Freedom of Information Act.
It says emissions are making natural disasters worse and warns that rising sea levels could undo more than half the development work in Bangladesh.
The internal report at the Department for International Development (Dfid) reveals the depth of concern shared by officials about climate change.
It forecasts that global warming threatens to reduce India's farm output by as much as a quarter - just as its population is booming. In Africa, the number of people at risk from coastal flooding is likely to rise from one million in 1990 to 70 million by 2080.
The Dfid report will increase pressure on the Prime Minister. Next week, the government publishes its review of Climate Change Strategy. It's committed to cutting emissions by 20% below 1990 levels but under Labour emissions have actually increased by 1.9%.
The report is Dfid's contribution to the UK government's review of climate economics being carried out by Nick Stern, former chief economist of the World Bank.
The Dfid report points that natural disasters cost donors $6bn annually. Seventy-three percent of them are climate related, so the bill will almost certainly soar if, as forecast, extreme weather events get much worse as the climate changes.
Dfid says the world will need to adapt to some degree to an inevitable measure of change fuelled by greenhouse gases already in the atmosphere; but it says all international development policies must be framed with climate change in mind.
It urges a target to stabilise greenhouse gas concentrations (a difficult goal as the US - the main emitter of these gases - refuses to discuss any such target). And it complains that the price of carbon is too low internationally to prompt cleaner development.
"It's crazy for the UK government to be talking a lot about climate change while at the same time our emissions are increasing," Farhana Yamin of the Institute of Development Studies at the University of Sussex, told the BBC.
"A great deal more action is needed domestically to reduce our carbon footprint which is going to have a massive impact on developing countries."
Until recently, the debate over climate change economics tended to have been dominated by industry lobby groups worried about the effect of clean-up measures on growth.
I understand that the Stern review is likely to predict that it will be much cheaper to reduce emissions than to attempt to deal with all the consequences of climate change.