Optimal Discount Rates for Investments in Mitigation and Adaptation

This paper develops a theory of asset pricing in which discount rates for investments in all assets, including adaptation and mitigation, are endogenously determined. Exploiting the characteristics of adaptation and mitigation in terms of climatic risk, I show that adaptation requires a lower discount rate, whereas mitigation does not. Inspection of the Ramsey rule reveals that the social discount rate equals the social rate of return on optimally-invested aggregate wealth minus the risk premium on that wealth. This risk premium compensates investors for bearing market risk and the risk of unfavorable changes in the economy resulting from climate change. This paper functions as an update of <a href="http://www.cpb.nl/en/publication/discounting-investments-mitigation-and-adaptation-dynamic-stochastic-general-equilibrium">Discussion Paper 126</a>.