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 \(\alpha\)-maxmin, minimax-regret, and multi-utilitarian criteria.

由于围绕贴现率的分歧，评估与气候变化相关的投资项目的收益变得复杂。众所周知，如果加权平均贴现率保持不变，更大的贴现率异质性会增加投资的加权平均现值，从而降低证明现在或永远不投资所需的最低内部收益率。较大的调整适用于寿命较长的项目。我将这个分析扩展到两个方向，首先是让决策者可以选择推迟投资。更大的贴现率异质性也增加了等待和重新评估未来投资的期权的加权平均现值。这削弱了贴现率异质性与最佳投资门槛之间的关系——并且在某些情况下实际上逆转了这种关系。当贴现率较低且项目的生命周期较短时，贴现率异质性的增加会导致更严格（而不是更容易）的最佳投资测试。第二个扩展检查了使用不同方法汇总有关贴现率的意见对这些结果的影响，包括\(\alpha\) -maxmin、minimax-regret 和多功利标准。