Often, numbers are derived from other processes, e.g. costed low carbon development strategies, yet it is difficult to ascertain whether the numbers were derived from a detailed cost analysis or based on broader extrapolations. In general, the methodological challenges associated with the economic assessment of mitigation and adaptation seem to be widely underestimated. A robust estimation of finance needs requires deep understanding and analysis of the specific policy and market context, in particular on barriers to the implementation of climate compatible alternative technologies or processes, and the elaboration of corresponding and sound investment plans.