Int. J. Environ. Res. Public Health 2011, 8 1012 four times lower. Similarly, the cost of each degree of mitigation would be at least four times higher since the effect of lowering CO2 levels would be less than one-fourth as much. So the economic benefits of mitigation would be only one-fourth as much while the overall cost of mitigation would remain the same but achieve less than one-fourth the global temperature reduction previously assumed. As a result the benefit-cost ratio of ―conventional‖ reductions in CO2 emissions would be less than one-fourth the levels previously calculated, all other things being equal. Thus the temperature increases to be mitigated would be less than one-quarter those assumed in the benefit studies, so the benefits of most proposed mitigation efforts would be less than one-quarter, but the cost of mitigating these damages would remain the same. Similarly, the much lower and empirically derived residence times for CO2 in the atmosphere greatly reduce the effectiveness of CO2 emissions reductions in decreasing atmospheric CO2 levels and therefore temperatures. There is much less of an increase in temperatures to offset, but the cost of offsetting them would be much the same as has previously been estimated by other analysts. 3.2. The Cost of Reducing Carbon Emissions Are Much Higher than Usually Assumed I have shown elsewhere that using the UN IPCC assumptions the 2 oC EU target is not likely to be achievable even at very high cost [55] (particularly pp. 712–716 and Appendix 1). The acronym ERD means exclusive regulatory decarbonization and is discussed further in Section 3.3 below. The following excerpt summarizes this finding [55] with a reference added: ―Even if climate sensitivity to increased CO2 is what the IPCC says it is, the modeling work by Rive et al. suggests that it would not only be risky but also very expensive to actually achieve the two degrees Celsius limit using ERD [56]. They find that to obtain a mere fifty percent chance of preventing more than a two degrees Celsius increase would require a global cut of eighty percent from current industrial emission levels by 2050 at a marginal cost of $3,500 per ton of carbon equivalent assuming average projections and ―early action‖ to reduce GHGs. $3,500 is roughly an order of magnitude higher than most previous estimates of marginal costs, presumably reflecting the extremely high cost of rapidly replacing most of the energy producing and using capital stock. An eighty percent cut would imply a reduction per person of about eighty-seven percent below current levels because of predicted world population growth. This appears to be of very doubtful practicality, particularly at the extremely high marginal costs estimated by Rive et al., and has a mere fifty percent chance of ―success‖ even in the ―ideal‖ world of modeling. This suggests that in the real world a serious effort to achieve such cuts would be extremely expensive, require worldwide cooperation and an early start, and be much more likely to lead to catastrophe than success….Rive et al. furthermore find that if we wait an additional ten years to implement serious emissions reductions, a fifty percent change would not be achievable at all, again assuming ―average‖ projections….The apparent implication is that even under a two degrees Celsius limit and three degrees Celsius sensitivity ERD is a very long shot with little real hope of meeting the two degrees Celsius limit even before taking into account the wide gap that is almost certain to exist between what is actually achieved and what countries and their citizens may agree to do.‖