This set of papers chiefly presents a critique of the IPCC's Special Report on Emissions Scenarios (SRES), which claims to “provide the basis for future assessments of climate change and possible response strategies”. The 40 scenarios are technically unsound in that, contrary to accepted international practice, they convert national GDP data to a common measure using market exchange rates. Because of this procedure and built-in assumptions about the extent to which the gap between rich and poor countries will be closed, the scenarios yield projections of GDP for developing regions which are improbably high: this includes the scenarios which give the lowest figures for projected cumulative emissions in the course of the century. Hence the SRES projections do not, as is claimed for them, encompass the full range of uncertainties about the future. Because of these and some other defects that we have noted, the SRES should not be taken as the accepted basis for the IPPC's coming Fourth Assessment Review. More broadly, the IPCC should try to ensure a more balanced, informed and professional treatment of the economic and statistical aspects of its work. In particular, there should be a greater involvement of economic ministries and statistical agencies.