Int. J. Environ. Res. Public Health 2011, 8 990 articles are published, but does not guarantee that the assumptions and hypotheses used represent valid science since the primary requirement for successful peer review is that other experts agree with the author. Particularly if enough experts agree on one particular viewpoint or if experts who do not agree are excluded from the peer review, peer-review does not guarantee scientific validity, the primary criterion used in this article. Unfortunately, the only useful way to deal with the inevitable application uncertainties is on a case-by-case basis. General rules such as only peer-reviewed, published research should be judged as valid may simplify decision-making, but impose substantial costs in terms of delays and the discouragement of new ideas, and in no way guarantee that all such research represents valid science. In the end, reasonable judgments have to be made. Much as economists might like to avoid these ―scientific‖ issues or may even feel unsuited to judge them, economists run the risk of grossly misleading their readers if they fail to deal with the major scientific (as well as economic) uncertainties and their economic implications. Where these uncertainties are very large, a reasonable conclusion may be that detailed benefit-cost analysis cannot play a useful role. But in most cases a careful analysis of the major scientific uncertainties will avoid the most serious risks of misinforming readers. At the very least, the approach used here provides a framework for deciding which physical science assumptions and hypotheses to accept and which to reject. This general approach has too often been lacking in discussions of climate change issues by economists as well as non-economists. In all too many cases these discussions have centered on prejudicial denigration of what the opposition is saying or the motives of the individuals saying it. It is only by using the most relevant observationally derived data and applying the scientific method that progress can be made on this and many other environmental and public policy interdisciplinary issues involving the physical sciences. The discussion should be centered on what the most relevant evidence shows, not who is making the argument. This paper can be viewed primarily as an attempt to apply the most relevant observational data and the scientific method to determine whether a few of the most economically critical assumptions and hypotheses are scientifically valid in the climate change case and what the economic implications of using other, more valid assumptions and hypotheses would be. Secondarily, it examines what the effects of ignoring lower cost mitigation alternatives are. As such, it has important methodological implications even if readers should disagree with the judgments reached as to the validity of some of the physical science assumptions and hypotheses central to the debate or with the validity of using lower cost alternatives. Some may argue that physical science decisions should be left to physical scientists and that economists should not get involved in the physical science aspects of policy choices they are evaluating; I argue, on the contrary, that there is no escape from making such judgments since using the scientific judgments of one side in a scientific argument assumes that that side is valid and the opposition side is invalid. The result is that the casual reader may not even realize that there is a difference of opinion and what effects that difference has on the economic analysis. All this will be illustrated by the case of climate change mitigation. Even if the reader should disagree with the particular judgments made in this article concerning the scientific validity or invalidity of various assumptions and hypotheses, I believe I have at least demonstrated the importance of explicitly explaining the effects of the major scientific uncertainties in any economic analysis with major interdisciplinary characteristics such as climate change mitigation. At the very least, I believe this