Policy interest in the cost of adaptation is growing, but compared to the mitigation literature adaptation cost research is still in its infancy. Global adaptation cost estimates from more recent studies range from around $25 billion a year to well over $100 billion by 2015-2030. The wide range is symptomatic of the poor state of knowledge. Important knowledge gaps remain both in terms of scope (whether all relevant impacts are covered) and depth (whether for a given impact all relevant adaptation options have been considered). The omissions introduce biases in both directions, upward and downward, but it is likely that adaptation costs have been underestimated so far. Adaptation is only one part of the overall response to (and therefore the costs of) climate change. The total burden of climate change consists of three elements: the costs of mitigation (reducing the extent of climate change), the costs of adaptation (reducing the impact of change), and the residual impacts that can be neither mitigated nor adapted to. The annual adaptation cost estimates reviewed here cannot be directly compared with the other two cost elements. Making this comparison would require an integrated model that takes into account the total impact of greenhouse gases over their lifetime in the atmosphere.
