Exploring carbon peak and carbon neutrality pathways for megacities from the perspective of supply and demand synergy: A LEAP simulation of the Beijing case

The transformation of urban energy systems under low-carbon constraints poses profound challenges for megacities, where rapid demand growth and limited local generation capacity often lead to structural imbalances between supply and demand. Using Beijing as a representative case, a refined Low Emission Analysis Platform (LEAP) framework was established to simulate 4 policy and 2 integrated scenarios during 2023–2060, examining how demand growth, supply decarbonization, and systemic resilience co-evolve. This study quantifies the critical supply–demand synergy threshold at the city scale, proposes a staged and temporally explicit decarbonization roadmap, and demonstrates that the energy transition is a dynamic and path-dependent process rather than a linear shift toward carbon neutrality. Specifically, total energy demand peaks around 2030 and then gradually declines, with renewables progressively replacing fossil-based generation to raise the share of non-fossil electricity above 70 % by 2060. The integrated Green Transport–Carbon Capture, Utilization and Storage (GT–CCUS) scenario achieves the earliest and deepest emission reductions, confirming that only the joint advancement of demand-side electrification and supply-side decarbonization—especially through large-scale renewables and CCUS as buffering mechanisms when renewables exceed roughly 50 % of the power mix—produces the most substantive system-wide benefits. Beyond emissions, the findings highlight that decarbonization can advance only upon a stable foundation of energy security and systemic resilience. As electrification accelerates, tensions between expanding demand and constrained supply may evolve from synergy to trade-off, and ultimately to antagonism if not managed adaptively. Ensuring a balanced transition therefore requires reinforcing grid flexibility, local generation reliability, and institutional adaptability to prevent systemic stress from undermining long-term climate goals. Beijing's experience proves that low-carbon development is not merely a technological substitution but a continual process of negotiating stability, efficiency, and sustainability within an increasingly interdependent urban energy system.