Several recent studies have reported adaptation costs for climate change, including for developing countries. They have similar-sized estimates and have been influential in discussions on this issue.

However, the studies have a number of deficiencies which need to be transparent and addressed more systematically in the future. A re-assessment of the UNFCCC estimates for 2030 suggests
that they are likely to be substantial under-estimates. The purpose of this report is to illustrate the uncertainties in these estimates rather than to develop new cost estimates, which is a much larger task than can be accomplished here. The main reasons for under-estimation are that: (i) some sectors have not been included in an assessment of cost (e.g. ecosystems, energy, manufacturing, retailing, and tourism); (ii) some of those sectors which have been included have been only partially covered; and (iii) the additional costs of adaptation have sometimes been calculated as