Identifying Urban CO2 Marginal Abatement Costs Under Alternative Reference Technologies: Evidence from 278 Chinese Cities

Urban CO2 marginal abatement costs (MACs) provide important information for designing sustainable low-carbon transition strategies, but their interpretation may be affected by reference technology choices and identification uncertainty. Using 5004 city-year observations from 278 Chinese prefecture-level cities over 2006–2023, this study applies a Global non-radial directional distance function to compare National and four-region Group reference technologies under identical baseline settings. At each fixed frontier projection, we characterize the complete admissible range of supporting shadow prices rather than select a single dual solution and assess sensitivity across seven prespecified modeling dimensions. Under the National benchmark, 87.31% of observations are bounded-set identified. National and Group identified sets overlap in 74.34% of city-years, indicating that strict benchmark ordering is uncommon. Across baseline–alternative comparisons, identification status changes in 9.87% of cases, whereas National–Group direction reversals occur in 0.84%; temporal technology generates the largest identification response (25.92%). Baseline numerical diagnostics show successful primal–dual solutions, unique projections, and no nesting violations. The results support more transparent sustainability-oriented assessments of urban decarbonization by reporting MACs together with identification status, benchmark choice, and specification sensitivity rather than as unconditional scalar values.