抄録
This study quantitatively assesses the adoption of carbon-offset city gas and its institutional, accounting-based greenhouse gas (GHG) offsetting effects in Japan’s city gas sector. As of October 2025, 55 of 190 city gas companies (29%) have adopted carbon-offset city gas, covering approximately 93% of national gas demand, with particularly high coverage in the Kanto, Chubu, and Kinki regions. Applying a CO₂ emission factor of 2.10 t-CO₂ per thousand m³ to an annual supply of 32.2 billion m³ (46 MJ/m³), combustion-stage emissions are estimated at 67.47 Mt-CO₂eq. Offsetting potentials are evaluated using three cases (1%, 5%, and 10%). Under the high-level 10% case, corresponding to the institutional upper limit of credit usage, approximately 6.75 Mt-CO₂eq can be offset, equivalent, under a consistent accounting framework, to about 40% of the Japan Gas Association’s 2030 reduction target. While these offsets represent accounting measures rather than physical emission reductions, they function as transitional tools that should be integrated with technologies such as CCUS, e-methane, and hydrogen for long-term decarbonization.
