Tham khảo tài liệu 'integrated waste management volume i part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Cost-Benefit Analysis of the Clean-Up of Hazardous Waste Sites 411 Time adjustment for environmental benefits and costs The cost and the benefit of a hazardous waste site cleanup especially in the case of permanent cleanup materialise over lengthy periods. Thus discounting plays a crucial role in the estimation of the value of future costs and benefits. Where different types of interventions are compared discounting future costs and benefits to present values renders them more easily comparable. Discounting implies that the further in the future the benefits and the costs occur the lower the weight that should be attached to them. Thus the general formula of discounting is the following Pearce et al. 2006 W 1 t 1 s t Where wt is the discount factor for time t and s is the discount rate. Thus the conversion of future benefits to a present value can be estimated with the following formula Presentvalue 2FutureValuet Xwt Where economists use discounting to adjust the value of costs and benefits occurring in the future the standard approach is to assume a constant discount rate common to both costs and benefits. For example since 1992 the US discount rate suggested as base case for costbenefit analyses was a fixed at 7 for both cost and benefit estimates. A 3 discount rate was also suggested for sensitivity analysis. The European Commission 2001 recommends for environmental cost benefit analyses the use of a discount rate of 4 and to perform sensitivity analyses using a discount rate of 2 and 4 . However there has been extensive discussion of whether the discount rate for health benefits should be lower than that applied to monetary costs. Also where the effects under consideration are long-lived the case for discount rates declining over time has been made. Mainly due to the lack of empirical studies there is uncertainty regarding the discount rate to be adopted in the economic evaluation of toxic waste cleanup interventions. A recent study conducted by Alberini et
