Over the past several years, a number of analysts have attempted to estimate the costs of adaptation for the developing world. This table summarizes these studies, their findings, and the methods and assumptions behind each. Viewing them together, several observations emerge:
The estimates suggest that tens of billions of dollars per year will be needed. However, specific ranges are broad, and the newest studies suggest that real costs could be substantially higher.
Overall, estimates remain extremely uncertain due to the unknown effects of climate change, and to the broad assumptions that must be made in calculating global costs.
The different estimates are closely related to each other, methodologically. Several are based on the methods presented in World Bank (2006), which focuses on the cost of “climate-proofing” financial flows for development. More recent studies have tended to take a sector-by-sector approach to estimating adaptation costs.
Users of these estimates should recognize that they are all broad international studies aimed at a global audience. None are calculated by aggregating national or regional estimates, and many of their assumptions are necessarily based on limited evidence. For several estimates, the rationale for key assumptions is not made explicit in the relevant reports.