Int. J. Environ. Res. Public Health 2011, 8 1022 effects should become imminent, if they ever do, since unlike CO2 emissions reductions the effects of SRM on global temperatures appear within months rather than decades. If indeed, Krugman is so concerned about the risks posed by such effects, he could have suggested a wait and see approach using these alternative approaches as a safety net, which is clearly the low cost approach to avoiding possible CAGW effects. Although Krugman [65] refers to Weitzman (presumably [81]), Weitzman recognizes the possibility of using a geoengineering approach as a way to avoid the risks from less than likely CAGW effects. The principal costs are some early but much more affordable research to better understand which geoengineering approaches offer the best approaches, how it could best be implemented, and building an institutional structure that would facilitate its use [62]. More generally, Krugman takes an interest in the relevant science, but fails to ask the crucial questions concerning whether his scientific understanding corresponds with the most relevant observational data and the scientific method and whether there may be lower cost mitigation alternatives. 5.2. Lomborg Lomborg [58] takes a somewhat different approach. He believes the climate models and that global warming will occur as they claim it will, but believes that there are other important problems that also need to be addressed in the world. He also has taken an interest in geoengineering and believes that it needs to be explored. So he is a moderate believer in the CAGW science, a strong believer that the costs of mitigation need to be reduced, primarily through a large tax-funded government research program, and that other alternatives need to be explored. So call him a moderate on the benefits of mitigation and a strong believer that costs can and need to be reduced if CO2 emissions are to be effectively reduced. The multidisciplinary approach taken by Lomborg on the cost side is consistent with that advocated here, but it appears that Lomborg did not use and may not have sought the critical climate science inputs on the benefits side such as those described in Section 2 above. He may also have overestimated the effectiveness of large government research efforts that are not very clearly focused on a particular promising technology. Clearly the Manhattan Project was successful in reaching its goals, but the same cannot be said for governmental efforts to carry out research on climate change/global warming [60]. In sum, Lomborg does not appear to question the science advanced by climate alarmists but does examine whether there are lower cost mitigation alternatives. 5.3. Relation between Analysts’ Assumptions and Policy Recommendations Although there have been some economics-only disagreements with regard to the economics of CAGW, principally with regard to the best discount rate to use and how to best value the benefits and costs involved, it appears that the physical science inputs used and other assumptions are at least as important in determining the policy recommendations arrived at. This article has emphasized the importance of the CSF and CO2 residence time in the atmosphere, which in turn determine the extent of the likely CAGW effects of global warming, the cost of improving energy efficiency, and whether geoengineering approaches are regarded as valid alternatives to reductions in GHG emissions as a mitigation approach.