Using an optimal control model to simulate carbon dioxide-biomass interactions
van Wassenhove, Ross Sherman
Hartley, Peter R.
Doctor of Philosophy
Many studies have proposed expansion of photosynthetic biomass "sinks" as a method of controlling atmospheric carbon dioxide. A defect in most of these studies is that biomass growth is assumed to be linear. In this thesis, optimal control theory is applied to an economic analysis of the interactions between global photosynthetic biomass growth and atmospheric CO2. The model assumes society starts with a fossil fuel resource endowment, which is used to supply energy. One goal is to determine numerically, using a "natural" model of the system, whether a steady state is reached in, the interactions between the biosphere and the atmosphere once the use of fossil fuel ceases. The thesis also determines, through a planet-level numeric simulation, optimal biomass and CO2 levels, and their associated "shadow prices" that would be required to ensure an efficient outcome in the presence of negative externalities associated with atmospheric CO2 (the "global warming problem"). The optimal solution is tested for sensitivities to changes in parameter values, including a "policy variable" of CO2 "tolerance". Biological growth is modeled by the logistic function, and CO2 sequestration is based on a non-linear C3 plant CO2 "fertilization" scheme. Alternative model structures to the logistical function are proposed and discussed. The model structure and numerical analysis derives some of its parameters from previous studies and estimations, but mainly the work of Hirofumi Uzawa.
Agricultural economics; Atmospheric sciences; Environmental science