This lecture by the instructor covers the comparison of environmental policy instruments, focusing on criteria such as environmental effectiveness, cost-efficiency, equity, and feasibility. It explains the concept of marginal cost and its role in determining optimal abatement levels. The lecture also discusses the cost-efficient allocation of mitigation efforts, the global cost of emissions reduction, and the importance of equal marginal abatement costs. Furthermore, it explores the reallocation of abatement efforts between different sources and presents case studies on the marginal abatement cost in the UK transport sector and world methane emissions. The goal is to provide insights into designing effective and economically efficient environmental policies.