The 80th session of the IMO Maritime Environment Protection Committee (MEPC 80) adopted the 2023 IMO Strategy on the Reduction of GHG Emissions from Ships (2023 IMO GHG Strategy), with enhanced targets to tackle harmful emissions. This study strives to provide an exact interpretation of the target of the 2023 IMO GHG Strategy and reveal the technical requirements therein. Decarbonization targets were expressed in IMO GHG emission scenarios for specifications. Model calculations and parameterizations were in line with IMO GHG reduction principles and decarbonizing practices in the shipping sector to avoid the prejudicial tendency of alternative fuels and the overestimated integral efficiency of short-term measures in existing predictions. IMO DCS data were used for the first time to gain reliable practical efficiencies of newly adopted regulations and further reduce the model uncertainty. The results demonstrated that the decarbonization goals for emission intensity were actually 51.5–62.5% in the IMO GHG reduction scenarios, which was much higher than the IMO recommended value of 40% as the target. Combined with the continuous applications of short-term measures, onshore power and regulations were required to contribute their maximum potential no later than the year 2030. Even so, considerable penetration (15.0–26.0%) of alternative fuels will be required by 2030 to achieve the decarbonization goals in the 90% and 130% scenarios, respectively, both far beyond the expected value in the 2023 IMO GHG Strategy (i.e., 5–10%). Until 2050, decarbonization from alternative fuels is required to achieve ~95%. Sustainable biodiesel and LNG are the necessary choices in all time periods, while the roles of e-methanol and e-ammonia deserve to be considered in the long term. Our findings highlight the intense technical requirements behind the 2023 IMO GHG Strategy and provide a pathway option for a fair and impartial transition to zero GHG emissions in the shipping sector, which might be meaningful to policymakers.

This study aims to predict the economic transition pathway for alternative fuels in accordance with the 2023 IMO GHG Strategy goals. The assessment considers the impact of alternative fuel transition on fuel costs (∆COST_Fuel,t), carbon emission costs (∆COST_{CO2 eq,t}), and ship new/retrofit costs (∆COST_ship). The parameters and boundary conditions were set based on the current status and trends in the international shipping industry, as determined from previous research, to predict the economic transition pathway for alternative fuels. The results show that in 2050, with a standardized economic efficiency of 130%, profit will reach its maximum value, approximately −54,000 million USD. The study standardized fuel ΔCOST_{j, normalized}, and ΔNPV%_{j, normalized} as a basis for adjusting penetration rates. At this time, considering fuel costs and NPV%, the composition of alternative fuels is as follows: bio-LNG, bio-Methanol, e-LNG, e-Methanol, e-Ammonia, BD, and Fossil-LNG, with shares of 18.56%, 4.00%, 25.64%, 6.00%, 10.00%, 28.00%, and 0%, respectively. Compared to conventional marine fuel HFO, the increase ranges from 23.54% to 69.50% in the 2030s, 0.52% to 0.55% in the 2040s, and decreases by 6.88%–14.69% in 2050. Using more LNG and BD in the 2040s and 2050 is an alternative way to achieve a better economic fuel transition. Moreover, the economic penetration rate combination set in this study can achieve sufficiently small ∆COST_T,t and sufficiently large NPV_Δt under specific assumptions and boundary conditions, rather than an absolute minimum ∆COST_T,t or the absolute maximum NPV_Δt. The results revealed that no single alternative fuel has a comprehensive advantage in reducing carbon intensity and economic performance at all times. Given the uncertainties in the supply chain, cost-effectiveness, and infrastructure for Methanol and Ammonia, LNG and BD play a crucial role in the transition of international shipping fuels. Our work provides a fundamental and comprehensive prediction of fuel transition based on the current status and trends in the international shipping industry.

To assess the economic impact of the draft Net-Zero Framework proposed by the International Maritime Organization at the 83rd session of the Marine Environment Protection Committee on shipping fuel transition, an economic assessment model incorporating fuel costs, carbon emission costs and newbuilding or retrofit investment costs was developed. The model compared the unit transition cost and net present value of alternative fuels. Four scenarios combining transport demand and surplus unit (SU) prices were established to analyze fuel transition costs and economic benefits from 2025 to 2050. Results revealed that a positive economic return was achieved only in the early stage under the high-demand and high-SU-price scenario. Under the other three scenarios, fuel transition would introduce additional costs to the shipping sector, up to USD 293.37 billion by 2050. Fuel price and greenhouse gas fuel intensity were identified as key parameters affecting transition costs, while the SU price had a limited impact on net-zero compliance. Biofuels exhibited better economic performance than e-fuels, and investments in all alternative-fuel-powered vessels were unlikely to be recouped. Targeted financial support mechanisms for electro-fuels and a phased flexible compliance framework are suggested.