A new study by NERA Economic Consulting, prepared for the National Association of Manufacturers (NAM), documents the economic dangers of a federal carbon tax. The study is very conservative in its assumptions (as I'll explain below), giving the benefit of the doubt to the proponents of a carbon tax. Even so, there study reaches two conclusions: Either the US government sets a carbon tax low enough so that its economic impacts are simply bad, but not awful, in which case there are few environmental benefits, or the US government sets a carbon tax aggressive enough to meet the emission goals that its proponents want, in which case it is economically devastating.