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.

在评估具有环境影响的长期公共项目时，对未来成本和效益进行贴现是一个至关重要但又颇具争议的做法。标准方法通常忽视了生态系统服务不易被市场商品替代，而且增长率往往要低得多。理论表明，我们应该要么采用差异化的贴现率，例如较低的环境贴现率，要么通过提高环境价值来解释相对稀缺性的增加。一些政府已经将其纳入其指导方针中，但经验证据很少。我们以德国为案例研究，提供了第一个全面的针对具体国家的证据。我们根据对德国 36 项支付意愿研究的荟萃分析，估算了 15 项生态系统服务的增长率和有限替代性程度。我们发现，近几十年来，生态系统服务的相对价格每年增长百分之四以上。异质性分析表明，相对价格变化对于调节生态系统服务最为显着。我们的研究结果强调了在政府项目评估和环境经济核算中考虑相对价格调整的重要性。