Indices for comparing greenhouse gas emissions: integrating science and economics

Abatement of greenhouse gases is a key element of possible policy responses to global warming. Comprehensive abatement strategies view the greenhouse abatement issue as one involving multiple gases and not CO₂ alone. These strategies require the formulation of greenhouse gas indices that will allow for an evaluation of the trade offs involved. This paper uses an optimal control methodology to determine greenhouse gas indices. Analytical expressions for the indices are determined using cost-benefit and cost-effectiveness framings. An integrated framework that includes the relevant scientific and economic processes is used to evaluate indices for methane, nitrous oxide and HCFC-22. Additionally, the optimal control problem for a two gas abatement strategy involving methane and carbon dioxide is numerically solved. In the case of methane, indices were calculated for direct as well as indirect radiative forcing effects. In addition to the numerical results, the analysis allows us to make several qualitative observations regarding the dependence of trace gas indices on the scientific and economic uncertainties involved in climate change policy.