A review on carbon emissions of global shipping

Abstract

Carbon dioxide (CO2) emissions from shipping account for about 3% of total annual anthropogenic CO2 emissions and are assumed to increase markedly without mitigation measures. Following the introduction of the net-zero emissions target, the large uncertainties and challenges of a low-carbon transition in the shipping industry have raised concerns in the scientific community. This study presents a compressive review of CO2 emission inventories for the shipping industry, examines the historical CO2 emission trends and associated estimation uncertainties due to different methodologies, and further discusses the CO2 reduction measures and potential published in the literature. We aim to answer what has happened and what will happen in the shipping industry to identify potential challenges in realizing a roadmap to net-zero emissions. Here we show that there is a 20% variation in CO2 emissions reported by the reviewed inventories due to differences in estimation methodology and study scope, with top-down approaches (e.g., IEA) advancing the timeliness of emission estimation and bottom-up approaches (e.g., CAMS-GLOB-SHIP and EDGAR) facilitating the availability of geospatial information. The rebound in CO2 emissions by 2021 underscores the urgency of decoupling growth in seaborne trade from carbon emissions, and source and process control measures will provide most of the abatement potential, leaving the remaining abatement burden to be borne by carbon capture and out-of-industry transfers by 2050. However, secondary emissions, navigational safety, crew welfare, international cooperation, and economic and technical feasibility pose challenges to current low-carbon development. There remains a long way to go towards realizing the goal of the net-zero target, it requires the coordination and cooperation of all operators along the entire value chain of the shipping industry.