A multiperiod model of an emissions trading system

Emissions trading systems (ETS) constitute a widely used tool to control greenhouse gas emissions and thus are vital to the global efforts to mitigate climate change. As most ETS' are divided into separate phases, this raises the policy question whether emissions allowances can be banked, that is, transferred to subsequent phases for later use. We provide a continuous-time stochastic ETS model in a multiperiod setting that can allow for banking across phases. In particular, we are able to represent the influence of emissions development on the value of banked allowances. We introduce two distinct approaches to the multiperiod model: A basic approach delivers a model that is analytically more tractable and computationally less costly, while our more complex two-dimensional approach entails a more realistic representation of the system. Numerical results show that banking decreases the mean emissions and increases allowance prices; at the same time, it increases the probability of complying with the emissions cap. In combination with the current penalty of the EU ETS at 100 Euro per ton, banking essentially guarantees compliance. We therefore conclude that banking is a crucial policy choice to improve the effectiveness and the reliability of an ETS.