Developing countries may need as much as $250-500 billion (203-406 billion euros) per year by 2050 to deal with the fallout from climate change, a UN report warned Friday.
The projected costs for adaptation were several times higher than previous estimates, said the United Nations Environmental Programme (UNEP), warning of a "significant funding gap after 2020."
"The impacts of climate change are already beginning to be factored into the budgets of national and local authorities," UNEP executive director Achim Steiner said in a statement.
"The escalating cost implications on communities, cities, business, taxpayers and national budgets merit closer attention as they translate into real economic consequences," he added.
Financing of developing country adaptation programs is a key sticking point at UN negotiations under way in Lima to hammer out the broad outlines of a new world pact to curb global warming.
Poor countries most vulnerable to climate change-induced impacts -- like extreme weather events, floods, droughts and sea-level rise -- are demanding that a rich nation commitment to adaptation and finance be written into the pact.
But many developed countries insist that the deal, due to be signed in Paris in December 2015 and to enter into force by 2020, should focus on mitigation -- meaning efforts to curb planet-warming greenhouse gas emissions.
Steiner said the new UNEP report "underlines the importance of including comprehensive adaptation plans in the agreement."
"Adaptation costs could climb as high as $150 billion by 2025/2030 and $250-500 billion per year by 2050," the report found.