Introduction

This paper focuses on the decarbonization of international shipping and its role in global climate mitigation strategies. The study uses integrated assessment models (IAMs) to analyze potential futures of maritime shipping under varying carbon budget scenarios. It seeks to align with the global ambition to keep warming below 2°C, emphasizing the use of low-carbon fuels and improvements in energy efficiency.

Current State of Maritime Shipping

Maritime shipping is a significant contributor to global CO2 emissions, accounting for about 2.8% of global totals. Historically, international shipping has focused on improving energy efficiency through regulations such as the Energy Efficiency Design Index (EEDI) and the Energy Efficiency Existing Ship Index (EEXI). In recent updates, the International Maritime Organization (IMO) aims for a 50% reduction in greenhouse gas (GHG) emissions from shipping by 2050 compared to 2008 levels, with newer targets pushing for net-zero life-cycle GHG emissions by 2050.

Challenges and Strategies for Decarbonization

Decarbonizing shipping faces several challenges, mainly due to the sector’s heavy reliance on fossil fuels and the long lifespan of ships, which creates a barrier to rapid changes in the fleet’s fuel use. The paper identifies low-carbon fuels such as biofuels, renewable alcohols, and green ammonia as critical to achieving deeper decarbonization. These fuels, alongside energy efficiency improvements, could reduce shipping emissions significantly, potentially aligning with the IMO’s ambitious 2050 targets.

Model Analysis and Findings

The study uses multiple IAMs to project scenarios from 2020 to 2100 under different carbon budgets. It finds considerable variability in the potential for emission reductions depending on the models’ assumptions about technology and fuel availability. Key findings include:

• High-resolution models, which consider a broader range of technological and fuel options, generally predict greater reductions in shipping emissions.
• Scenarios aiming for stringent carbon budgets (like 600 GtCO2 from 2020 to 2100) show potential for significant emission reductions, aligning with a pathway to keep warming below 1.5°C.
• The transition to alternative fuels is crucial, with different models favoring different fuels based on their underlying assumptions about global energy trends.

Implications for Policy and Future Research

The paper underscores the need for comprehensive strategies that include both immediate and long-term measures to reduce shipping emissions. These include adopting new fuel technologies, improving energy efficiency, and developing infrastructure for new fuel types. The study also highlights the importance of integrated approaches that consider the broader energy system’s evolution, which will influence the availability and viability of various low-carbon fuel options for shipping.

The research points to a need for ongoing evaluation of policy measures, technological advancements, and market developments that could influence the feasibility and effectiveness of proposed strategies to decarbonize shipping. Future research could further explore the economic impacts of decarbonization, such as the effects on shipping costs and competitiveness.

Conclusion

Achieving significant reductions in shipping emissions is feasible but requires a coordinated global effort that embraces technological innovation and stringent climate policies. The transition to low-carbon fuels, alongside continued improvements in energy efficiency, forms the backbone of the strategies needed to align international shipping with global climate goals.