By Richard Black
Environment correspondent, BBC News website
African countries are likely to need help in adapting to drier conditions
Adapting to impacts of climate change will cost $75-100bn (£47-63bn) per year in the developing world from 2010, a World Bank study concludes.
The bank released preliminary findings from its new global study at the latest round of UN climate talks in Bangkok.
The figures assume that temperatures rise by 2C (3.6F) in the next 40 years.
How to finance adaptation, and how much money will be available, is a major theme in the talks that are supposed to produce a new global treaty this year.
The major costs would come from improving coastal protection and protecting transport links, the bank says.
The figures are more precise than previous estimates by UN agencies and development charities.
"One of the ways our analysis differs is that it's the first to establish a baseline that includes economic growth," Warren Evans, director of the bank's environment department, told BBC News.
"Most of the previous studies assumed that Bangladesh in 2050, for example, would be the same as it is today, and obviously it's not going to be like that - hopefully there'll be less poverty and more growth and so on - and that has major impacts on the costs of adaptation."
The bank found that costs would differ according to rainfall in a world that has warmed 2C from pre-industrial times, with wetter conditions implying a higher overall pricetag.
Developing countries say that as western nations grew prosperous largely through burning fossil fuels, they have a duty to finance protection around the world.
The principle is accepted by some developed countries, and a number of proposals are on the table.
UK Prime Minister Gordon Brown has proposed setting up a $100bn fund for adaptation money, and last month the European Commission published suggestions on how the burden might be shared between funding nations, and between the public and private sectors.
The costs of staple foods such as rice are projected to rise
But consensus has yet to be reached between governments trying to negotiate the new UN climate treaty.
The World Bank notes that the $75-100bn sum is roughly equivalent to existing levels of overseas aid.
"This study makes plain that taking action in favour of adaptation now can result in future savings and reduce unacceptable risks," said Bert Koenders, the Dutch Minister for Development Co-operation.
"For poor countries, [the costs] are unacceptably high. International public financial support for adaptation in the poorest developing countries should be new and additional, so as not to jeopardise the Millennium Development Goals."
The Dutch government is co-funding the World Bank study, along with Switzerland and the UK.
One analysis that departed dramatically from the $100bn per year ballpark emerged last month from the International Institute for Environment and Development (IIED) and the Grantham Institute.
It suggested the true costs would be double or even treble that amount.
It cited examples such as a Chinese study showing that the cost of adapting a single watershed would come in at $1bn per year.
Professor Martin Parry, who led the IIED report, said the World Bank appeared to have omitted some significant elements from its analysis.
"The biggest of these is the cost of adapting ecosystems, which could cost as much again, even if it were possible," he said.
"And then there are other sectors that are not included, such as manufacturing, mining, energy and tourism, each of which would have an adaptation cost."
The overall cost would also be higher if temperatures rose by more than 2C.
Earlier this week, a new UK projection suggested that if the world's energy use continued along its current trajectory, a rise of 4C was likely by 2070.
The World Bank will release further details before December's UN climate summit in Copenhagen, with the full report due out in March.