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In this paper I offer a fairly complete account of the idea of social discount rates as applied to public policy analysis. I show that those rates are neither ethical primitives nor observables as market rates of return on investment, but that they ought instead to be derived from economic forecasts and society's conception of distributive justice concerning the allocation of goods and services across personal identities, time, and events. However, I also show that if future uncertainties are large, the formulation of intergenerational well-being we economists have grown used to could lead to ethical paradoxes even if the uncertainties are thin-tailed. Various modelling avenues that offer a way out of the dilemma are discussed. None is entirely satisfactory.

Our knowledge of discount rates plays an important role both in the discounted cash flow decision-making process and in the later phases of a project’s lifetime. It is useful than both for management and cash-flow monitoring purposes at operating stages. Investors putting money into power generation projects expect an appropriate rate of return to compensate them for a minimum acceptable real return available in the market (risk-free rate of interest) and the project’s specific risk. Due to its essential nature in the financial and economic evaluation of projects (it is the only parameter that reflects the risk), it is reasonable to assume that investors would also be interested in constituent components of that indicator. The discount rate is one parameter in the discounted cash flow analysis that takes into account the risk of a venture. Further, the previous research in this area has focused mainly on the dimension of this variable, and the structure of this parameter has not been dealt with any other studies. The proposed idea of this study met the expectations of the industry—it aimed to present a typical project implemented in the energy industry, a relatively simple methodology that allowed estimating the components within the cost of equity capital of the enterprise. In the power generation sector, one can find various types of discount rates—assessed for multiple technologies, at different development stages, and expressed differently. Owing to the know-how and decades-long experience, coal-fired power projects’ remarks may be a good benchmark for alternative low carbon technologies. That is why, in this work, a discount rate for valuing investment in new coal-fired power projects was evaluated. This assessment was made on the “bare-bones” assumption, meaning evaluations at 100% equity, after-tax, in constant (real) currency units. The analysis of the discount rate structure was performed by applying the procedure of the classical sensitivity analysis having the accuracy of key input parameters. Finally, the risk factors within the risk-adjusted discount rate were calculated. The obtained results showed the importance of individual risk factors within the risk-adjusted discount rate used in coal energy projects, which would enable a more pragmatic approach to controlling this parameter by decision-makers and understanding the risk.

The economic values of investing in long-term public projects are highly sensitive to the social discount rate (SDR). We surveyed over 200 experts to disentangle disagreement on the risk-free SDR into its component parts, including pure time preference, the wealth effect, and return to capital. We show that the majority of experts do not follow the simple Ramsey Rule, a widely used theoretical discounting framework, when recommending SDRs. Despite disagreement on discounting procedures and point values, we obtain a surprising degree of consensus among experts, with more than three-quarters finding the median risk-free SDR of 2 percent acceptable.

This paper provides novel empirical evidence on the value of the elasticity of marginal utility, \\[ \\eta \\], for the United Kingdom. \\[ \\eta \\] is a crucial component of the social discount rate (SDR), which determines the inter-temporal trade-offs that are acceptable to society. Using contemporaneous and historical data, new estimates are obtained using four revealed-preference techniques: the equal-sacrifice income tax approach, the Euler-equation approach, the Frisch additive-preferences approach and risk aversion in insurance markets. A meta-analysis indicates parameter homogeneity across approaches, and a central estimate of 1.5 for \\[ \\eta \\]. The confidence interval excludes unity, the value used in official guidance by the UK government. The term structure of the SDR is then estimated. The result is a short-run SDR of 4.5% declining to 4.2% in the very long-run. This is higher and flatter than the UK official guidance. The difference stems from incorrect calibration of social welfare and estimation of the diffusion of growth. Other things equal, the results suggest that current UK guidance might need to be updated.

The concept of risk is well known in the energy sector. It is normally recognized when it comes to price and cost forecasting, annual production calculation, or evaluating project lifetime. Nevertheless, it should be pointed out that the quantitative evaluation of risk is usually difficult. The discount rate is the only parameter reflecting risk in the discounted cash flow analysis. Therefore, knowledge of the discount rate along with the major components affecting its level is of fundamental significance for making investment decisions, capital budgeting, and project management. By referring to the standard coal-fired power generation projects the authors of the paper tackle the analysis of the composition of discount rate for onshore wind farm technologies in the Polish conditions. The study was carried out on the basis of a typical (hypothetical) onshore wind farm project assessed at the feasibility stage. To enable comparisons and discussions, it was assumed that the best reference point for such purposes is the real risk-adjusted discount rate, RADR, after-tax, in all equity evaluations (the ‘bare bones’ assumption); that is because such a rate reflects the inherent characteristics of the project risk. The study methodology involves the a priori application of the discount rate level and subsequently—in an analytical way—calculation of its individual components. The starting point for the analysis of the RADR’s composition was the definition of risk, understood as the product of uncertainty and consequences. Then, the risk factors were adopted and level of uncertainty assessed. Subsequently, using the classical sensitivity analysis of IRR, the consequences (as slopes of sensitivity lines) were calculated. Consequently, risk portions in percentage forms were received. Eventually, relative risks and risk components within cost of equity were assessed. Apart from the characteristics of the discount rate at the feasibility stage, in the discussion section the study was supplemented with an analogous analysis of the project’s cost of equity at the operating stage.

Energy policy investments are usually evaluated using a cost-benefit analysis (CBA), which requires an estimation of the social discount rate (SDR). The choice of SDR can be crucial for the outcome of the appraisal, as energy-related investments generate long-term impacts affecting climate change. Once discounted, these impacts are highly sensitive to slight changes in the value of the SDR. Some countries (the UK and France) switched from a constant SDR to the declining rate scheme—a solution that limits the impact sensitivity. To our knowledge, none of the CEE countries apply DDR in CBA. While a constant SDR is a relatively well-established approach, declining SDRs are estimated to be used much less frequently, particularly for CEE EU member countries and energy policies. The rationale for the decline can rest on uncertainty over future discount rates, as shown by the approach developed by Weitzman and Gollier, which extends the classical Ramsey model. We applied this approach in our paper, as the Ramsey formula is the prevailing formula for EU countries’ SDR estimates. We estimated a flat SDR via the Ramsey formula with Gollier’s “precautionary term”, and next, we calculated Weitzman’s certainty equivalent rates for the 500-year horizon. Ramsey’s SDRs, obtained using consumption growth rates dating back to 1996, varied between 6.77% for Lithuania and 2.95% for Czechia and declined by 0.15% on average (Gollier’s term). Declining SDRs for the longest horizon dropped to approx. 0.5% (from 0.35% for Bulgaria to 0.67% for Poland), and the descent is deeper and faster when forward SDRs (following the UK Green Book approach) were considered (0.01% to 0.04%). The results are important for long-term policies regarding energy and climate change in CEE EU member countries, but they are still dependent on fossil fuels and experience an investment gap to fulfil EU climate goals.

Evaluating the benefits of investment projects related to climate change is complicated by disagreements surrounding the discount rate. It is widely known that greater discount-rate heterogeneity increases the weighted-average present value of investing if the weighted-average discount rate is held constant, which therefore reduces the minimum internal rate of return needed to justify now-or-never investment. A larger adjustment is appropriate for projects with longer lives. I extend this analysis in two directions, first by giving the decision-maker the option to delay investment. Greater discount-rate heterogeneity also increases the weighted-average present value of the option to wait and reevaluate investment in the future. This weakens the relationship between discount-rate heterogeneity and the optimal investment threshold—and in some cases actually reverses it. When discount rates are low and the project’s lifetime is short, increases in discount-rate heterogeneity can lead to tougher (not easier) optimal investment tests. The second extension examines the effect on these results of using different approaches to aggregate opinions about the discount rate, including the α-maxmin, minimax-regret, and multi-utilitarian criteria.

The importance of the discount rate in cost-benefit analysis of long term problems, such as climate change, has been widely acknowledged. However, the choice of the discount rate is hardly discussed when translating policy targets-such as 1.5 °C and 2 °C-into emission reduction strategies with the possibility of overshoot. Integrated assessment models (IAMs) have quantified the sensitivity of low carbon pathways to a series of factors, including economic and population growth, national and international climate policies, and the availability of low carbon technologies, including negative emissions. In this paper we show how and to what extent emission pathways are also influenced by the discount rate. Using both an analytical and a numerical IAM, we demonstrate how discounting affects key mitigation indicators, such as the time when net global emissions reach zero, the amount of carbon budget overshoot, and the carbon price profile. To ensure inter-generational equity and be coherent with cost-benefit analysis normative choices, we suggest that IAMs should use lower discount rates than the ones currently adopted. For a 1000 GtCO2 carbon budget, reducing the discount rate from 5% to 2% would more than double today's carbon price (from 21 to 55 $/tCO2) and more than halve the carbon budget overshoot (from 46% to 16%), corresponding to a reduction of about 300 GtCO2 of net negative emissions over the century.

Discounting future costs and benefits is a crucial yet contentious practice in the appraisal of long-term public projects with environmental consequences. The standard approach typically neglects that ecosystem services are not easily substitutable with market goods and often exhibit considerably lower growth rates. Theory has shown that we should either apply differentiated discount rates, such as a lower environmental discount rate, or account for increases in relative scarcity by uplifting environmental values. Some governments already integrate this into their guidance, but empirical evidence is scarce. We provide first comprehensive country-specific evidence, taking Germany as a case study. We estimate growth rates of 15 ecosystem services and the degree of limited substitutability based on a meta-analysis of 36 willingness to pay studies in Germany. We find that the relative price of ecosystem services has increased by more than four percent per year in recent decades. Heterogeneity analyses suggest that relative price changes are most substantial for regulating ecosystem services. Our findings underscore the importance of considering relative price adjustments in governmental project appraisal and environmental-economic accounting.

The growing environmental concerns require the characterization of decision support methods that can guide analysts towards more sustainable investment choices. Therefore, in the ex-ante economic evaluations of investments with environmental repercussions, it is of rising interest to give the “right” value to the non-monetary effects in the long term. In this regard, conventional discounting procedures—based on constant rates—are inadequate to evaluate intergenerational environmental effects. With this research we propose an innovative model for estimating discount rates to be used in the Cost–Benefit Analysis (CBA) of projects with long-term environmental effects. The model is based on a two-goods extension of the Ramsey formula, according to which the rate at which environmental impacts are discounted is different from the rate at which monetary benefits are discounted. Compared to the Ramsey model, we propose time-declining functions of the two discount rates to assess the long-run effects of investment projects. To characterize the model, we consider the macroeconomic risk, or we assume that the variable “GDP growth rate” is a stochastic variable. Furthermore, since we propose discount rates to evaluate public projects in line with sustainable development goals, we express environmental quality as a function of the Environmental Performance Index (EPI). Based on the proposed model, we estimate for the first time declining consumption discount rates and declining environmental discount rates for Italy based on empirical data. The estimates of the two discount rates for Italy shows that the environmental discount rate is lower than the consumption one: in fact, the first one starts from a value of 3.0% and arrives at 0.4% after 300 years; while the second one starts from 0.7% and reaches 0.3% at the end of the considered time horizon. The result highlights the importance of estimating country-specific dual and declining discount rates. These discount rates allow appropriate weights to be given to all investment impacts, and therefore also to environmental impacts, compared to conventional discounting.