an unresolved debate in the economics literature revolves around the question of whether discount rates should be positive (descriptive), reflecting actual market rates of, or normative (prescriptive), reflecting ethical considerations. those who argue for the descriptive approach prefer to use market rates of return since expenditures to mitigate climate change are investment expenditures. those who argue for the alternative prescriptive approach argue for including judgments about intergenerational equity. these rates are usually lower than those found in actual markets