Intertemporal Permit Trading for the Control of Greenhouse Gas Emissions

This paper integrates two themes in the intertemporal permitliterature through the construction of an intertemporal bankingsystem for a pollutant that creates both stock and flow damages. A permit banking system for the special case of a pollutant thatonly causes stock damages is also developed. This latter,simpler case corresponds roughly to the greenhouse gas emissionreduction regime proposed by the U.S. Department of State as ameans of fulfilling the U.S. commitment to the FrameworkConvention on Climate Change. This paper shows that environmentalregulators can achieve the socially optimal level of emissionsand output through time by setting the correct total sum ofallowable emissions, and specifying the correct intertemporaltrading ratio for banking and borrowing. For the case ofgreenhouse gases, we show that the optimal growth rate of permitprices, and therefore the optimal intertemporal trading rate, hasthe closed-form solution equal to the ratio of current marginalstock damages to the discounted future value of marginal stockdamages less the decay rate of emissions in the atmosphere. Given a non-optimal negotiated emission path we then derive apermit banking system that has the potential to lower net socialcosts by adjusting the intertemporal trading ratio taking intoaccount the behavior of private agents. We use a simplenumerical simulation model to illustrate the potential gains fromvarious possible banking systems.