Carbon intensity diagnostics for global crude oil ports: Linking AIS trajectories and economic contributions

Crude oil shipping is constrained by the significant geographical separation of production from consumption, necessitating extensive non-revenue-generating ballast voyages that contribute substantially to maritime emissions. However, existing decarbonization regulations treat all transport activities uniformly, overlooking the misalignment between carbon liabilities and economic value generation. To bridge this gap, this study identifies ports as the critical nexus and constructs an integrated framework by coupling Automatic Identification System (AIS) data with an Inter-Country Input-Output (ICIO) model to evaluate the carbon-economic intensity of 405 ports. Ballast voyage emissions are back-allocated to subsequent laden voyages, explicitly aligning carbon accounting with standard charter-party arrangements. Based on this approach, three indicators are proposed: the Port Carbon Intensity Index (PCII), Port Emission–Output Tradeoff (PEOT), and Port Demand Emission Multiplier (PDEM). Results indicate that: (i) high-income economies exhibit the highest median PCII, indicating a misalignment between economic scale and logistical carbon-economic performance; (ii) ballast voyages are a critical factor, accounting for 28–40% of port-associated emissions; and (iii) Middle Eastern hubs function as high-cost bottlenecks driven by East Asian demand, whereas high-leverage nodes like Singapore demonstrate higher mitigation efficiency. The framework facilitates the internalization of carbon costs into commercial contracting, providing actionable benchmarks for decision-making under common sales contracts and chartering agreements.