Optimal greenhouse gas emission pathways for South Korea from 2031 to 2049: An optimal control theory perspective

On August 29, 2024, the Constitutional Court of Korea issued a decision of nonconformity regarding Article 8, Paragraph 1 of the Carbon Neutrality Act, mandating a quantitative specification of the emissions pathway between the 2030 Nationally Determined Contribution and the 2050 net-zero target. This ruling is expected to stimulate extensive academic and policy discussions on the necessary pathway. While the exact shape of the emissions pathway may vary according to philosophical approach, three primary forms can be considered: concave, linear, and convex. This study employs optimal control theory to clarify the form and characteristics of an optimal emissions pathway. Cost minimization is the preferred criterion, acknowledging that the optimal pathway may differ depending on the selected criterion. The resulting emissions pathway is convex and downward-sloping, indicating that greenhouse gas reductions should be implemented as early as feasible. The pace of reduction is dependent on the relative magnitude of the social cost of carbon and mitigation costs: a larger social cost of carbon results in a more pronounced convex emissions pathway. Determining the exact shape of the optimal emissions path requires knowledge of the values of both the social cost of carbon and mitigation costs, which are still subjects of ongoing debate. Consequently, this study suggests that the government should establish a plausible range for these two costs, rather than seeking scientifically exact values, to determine the emissions path for the period 2031 ~ 2049.