Life-cycle energy and environmental emissions of cargo ships

Maritime shipping is under increasing pressure to alleviate its environmental impact. To this end, life-cycle footprint accounting provides a foundation for taking targeted measures in the green transition of shipping. This study used the process-based hybrid life-cycle inventory (LCI) modeling approach to estimate the "cradle-to-propeller" footprint of ships, including primary energy consumption, carbon dioxide emissions, and sulfur dioxide emissions. We used the input-output LCI model to calculate the embodied energy and emissions associated with the material and fuel use of ship manufacturing. We used a bottom-up emission model and global marine traffic data to estimate the operational footprint of different types of ships. Based on 382 cargo ships (including bulk carriers, container ships, and general cargo ships) constructed in mainland China between 2011 and 2015, we estimated that the embodied footprint accounted for <10% of the cradle-to-propeller footprint under the pre-2019 policy scenario. In terms of life-cycle energy intensity (MJ/nm/1000 deadweight tonnage [DWT]), the large bulk carrier (>100,000 DWT) establishes the lowest value (46), followed by the small (0-100,000 DWT) bulk carrier (96), the large container ship (133), the small container ship (196), and the small general cargo (238). The bulk carrier was identified as the most energy efficient among the three ship types, and ships with larger capacities (i.e., DWT) had higher energy efficiencies than ships with lower capacities. Our study provides a comprehensive understanding of the life-cycle footprints of cargo ships, thus enabling better evidence-based policymaking to transition the global marine-shipping industry to a future of greener energy.