IMO Short-term Measures: A Review of the Carbon Intensity Indicator (CII)

The Carbon Intensity Indicator (CII) is one of the short-term measures introduced by the International Maritime Organization (IMO) to reduce greenhouse gas emissions from shipping. This policy brief reviews the measure and provides improvement recommendations, focusing on how emission standards at sea and at port should be dealt with.

Key Highlights:

  • CII is currently insufficient for capturing emissions accurately at sea and at port and incentivising emission reduction
  • A range of revision options could be considered such as excluding port emissions, adjustments for time at port, or separate metrics for at sea and at port
  • Other areas that could be considered include allowance for actual cargo, well- to-wake emissions, and pilot fuel

Recommended revision for CII is to use separate metrics for at sea and at port emissions.

This policy briefing is based on research undertaken by Dr Ioannis Moutzouris, Dr Yao Shi, and Dr Claire Copeland.

Scheduling heterogeneous yard cranes for port decarbonization: power constraints, crane interference, and safety distances

“Abstract

Yard equipment upgrades are vital for port decarbonization, yet the coexistence of legacy and new yard cranes creates challenges in coordinating operations and allocating limited electrical power. This paper studies the integrated container allocation and conflict-free scheduling of multiple yard crane types, including slipline rail-mounted gantry crane (RMG), hybrid diesel-electric RMG, cable rubber-tyred gantry crane (RTG), and diesel-powered RTG, under power capacity, interference, and safety-distance constraints. We propose a mixed-integer linear programming (MILP) model that minimizes energy cost, carbon penalty, and makespan penalty. Because general-purpose solvers struggle with large instances, we develop a tailored logic-based Benders decomposition (TLBBD) algorithm with several enhancement strategies. Numerical experiments based on data from a real port demonstrate that TLBBD significantly outperforms Gurobi, an existing LBBD method, and real-world scheduling schemes, obtaining optimal or near-optimal solutions within 15 minutes for instances with five cranes and 100 containers. Sensitivity analyses on cable RTG cable length, yard crane layout, and carbon tax further illustrate the practical applicability of the proposed approach.”

 

Liu, B., Wang, F., Sheng, D., Zhang, X., Zheng, J. and Song, D. (2026). Scheduling heterogeneous yard cranes for port decarbonization: power constraints, crane interference, and safety distances. Transportation Research Part E: Logistics and Transportation Review, 206, p.104581. doi:https://doi.org/10.1016/j.tre.2025.104581.

The full report is accessible via: https://doi.org/10.1016/j.tre.2025.104581

For related publications, please see Resources – UK National Clean Maritime Research Hub

Policy Bulletin 006: Regional Ports – economic and emissions advantages

Maritime policy bulletin 006 covers the economic and emissions advantages of regional ports.

Ports and shipping are subject to increasing pressure to decarbonise. This provides opportunities to reconsider shipping routes and to enhance port competitiveness. This bulletin provides an overview of an economic and environmental impact assessment of rerouting Asia-Europe deep sea container ships via the Port of Liverpool as a case study.

The findings could support a place-based policy strategy to promote the use of regional ports in deep-sea container shipping. This would lead to lower logistics costs and lower emissions contributing to achieving national decarbonisation targets.

This bulletin is based on a recent publication by Prof. Dong-Ping Song titled Rethinking Routes: The Case for Regional Ports in a Decarbonizing World.

To download the full policy bulletin, please click the download button above.

To read other bulletins, please see: Resources – UK National Clean Maritime Research Hub

State of the Art in Wind Assisted Ship Propulsion for Maritime Decarbonisation and Sustainable Shipping: A Systematic Review

“Abstract

The advent of modern wind propulsion systems (WPS) to answer contemporary and forthcoming regulatory requirements to reduce shipping emissions has prompted the development of multiple technologies, ranging from sails to rotating cylinders, to kites. However, as the benefits of WPS for wind-assisted ships are still based on predictions due to the lack of operational, on-water data, the most promising technologies and areas of future research remain unclear. Moreover, the lack of consistent research methodologies and test conditions has led to large reported divergences in the potential of WPS in the literature. Consequently, to ascertain the comparative potential of WPS to reduce shipping emissions and present the state of the art in wind propulsion for ships, a systematic review is undertaken, with the aim to quantify the carbon dioxide (CO2) emission reductions associated with each type of WPS. The systematic literature review methodology ensures unbiased results, while accurately reporting the latest research developments in the field. Here we quantify the benefits of WPS, with an average 17% reduction in CO2 emissions, with an interquartile range from 7.5% to 22.5%. Moreover, we identify Flettner rotors as both the most studied and most commonly installed WPS, and note a discrepancy for suction wings, with a large share of installed WPS, but only very little published research. Additionally, we critically appraise current practices in the analysis of WPS, ranging from true wind and ship speed to the vessel type and size. These findings provide a novel and holistic overview of wind propulsion of ships, as well as the first systematic review on the topic, allowing an unbiased assessment of wind propulsion for ships. It is anticipated that these results may inform future research directions in sustainable shipping, and inform policymakers on the benefits of wind propulsion to meet emission regulations. Moreover, recommendations for more consistent reporting of WPS studies have been provided to support future global research and enable quantitative comparison across all published work.”

 

Huang, J. and Souppez, J.-B. (2025). State of the Art in Wind Assisted Ship Propulsion for Maritime Decarbonisation and Sustainable Shipping: A Systematic Review. Journal of Sailing Technology, 10(01), pp.258–278. doi:https://doi.org/10.5957/jst/2025.10.1.258.

The full report is accessible via: https://doi.org/10.5957/jst/2025.10.1.258 

 

For related publications please see Resources – UK National Clean Maritime Research Hub

Rethinking Routes: The Case for Regional Ports in a Decarbonizing World

“Abstract

Background: Increasing regulatory pressure for maritime decarbonization (e.g., IMO CII, FuelEU) drives adoption of low-carbon fuels and prompts reassessment of regional ports’ competitiveness. This study aims to evaluate the economic and environmental viability of rerouting deep-sea container services to regional ports in a decarbonizing world. Methods: A scenario-based analysis is used to evaluate total costs and CO2 emissions across the entire container shipping supply chain, incorporating deep-sea shipping, port operations, feeder services, and inland rail/road transport. The Port of Liverpool serves as the primary case study for rerouting Asia–Europe services from major ports. Results: Analysis indicates Liverpool’s competitiveness improves with shipping lines’ slow steaming, growth in hinterland shipment volume, reductions in the emission factors of alternative low-carbon fuels, and an increased modal shift to rail matching that of competitor ports (e.g., Southampton). A dual-port strategy, rerouting services to call at both Liverpool and Southampton, shows potential for both economic and environmental benefits. Conclusions: The study concludes that rerouting deep-sea services to regional ports can offer cost and emission advantages under specific operational and market conditions. Findings on factors and conditions influencing competitiveness and the dual-port strategy provide insights for shippers, ports, shipping lines, logistics agents, and policymakers navigating maritime decarbonization.”

 

Song, DP. (2025). Rethinking Routes: The Case for Regional Ports in a Decarbonizing World. Logistics, 9(3), 103.

The full report is accessible via: https://doi.org/10.3390/logistics9030103

 

For related publications please see Resources – UK National Clean Maritime Research Hub

Predicting out-terminals for imported containers at seaports using machine learning: Incorporating unstructured data and measuring operational costs due to misclassifications

“Abstract

Persistent bottlenecks at container ports have significantly disrupted global supply chains, necessitating more efficient operations at seaports to address yard density and port congestion. An untapped but potentially critical approach to mitigating these challenges is to leverage container characteristics and machine learning to predict the out-terminals of containers upon their discharge from vessels. The predicted results can then guide the development of a more effective container storage strategy. To formulate such a strategy, this research developed a data-enabled methodological framework that integrates four key components: 1) Utilization of structured and unstructured data to enhance prediction accuracy. 2) Practice and knowledge-informed feature engineering to construct relevant features for the machine learning models. 3) Explanatory machine learning based classification models to understand the factors influencing terminal predictions. 4) Model-induced cost analysis to capture the monetary value of the prediction model including assessing the cost implications of misclassifications. An empirical study conducted at a seaport shows that our framework yields cost savings ranging from 14.90% to 30.45% compared to the Business-as-Usual scenario. Incorporating unstructured data as an additional feature in the machine learning models improves prediction performance by up to 6%. Moreover, integrating this framework into the existing operational system poses minimal risk and can be seamlessly executed. Additionally, the proposed methodological framework and its four components has broad applications beyond the shipping industry.”

 

Xie, Y., Song, DP, Dong, JX and Feng, YJ (2025). Predicting out-terminals for imported containers at seaports using machine learning: incorporating unstructured data and measuring operational costs due to misclassifications, Transportation Research Part E, (accepted in June 2025).
https://doi.org/10.1016/j.tre.2025.104331.

The full report is accessible via: https://doi.org/10.1016/j.tre.2025.104331

 

For related publications please see Resources – UK National Clean Maritime Research Hub

Policy Bulletin 003: The economics of shipping decarbonisation

Maritime Policy Bulletin 003 explores the economics of shipping decarbonisation, offering financial insights into how effectively the maritime industry is aligning environmental objectives with economic performance.

Drawing on recent research by Dr. Yao Shi and Dr. Ioannis Moutzouris of City St. Georges, University of London, this bulletin presents a summary of allocation efficiency across 14 vessel types. It highlights key findings on carbon efficiency and provides financial perspectives that inform actionable policy recommendations aimed at accelerating the adoption of greener fuels.

To download the full policy bulletin please click the download button above.

To explore other bulletins, visit:  Resources – UK National Clean Maritime Research Hub

Clean Maritime Assembly – Highlights and Headlines Presentations (Day 2)

Lightning-style presentations from industry and academia, showcasing clean maritime activity across the sector.

The following presentations are available for view as part of our Resources Library.

Session 1 – Ports: Chaired by Prof Sarah Sharples, Department for Transport

  • Prof Trung Thanh Nguyen, Liverpool John Moores University: “Efficiency optimisation to make port operations greener”
  • Kirsty Gouck, Connected Places Catapult: “Enabling Net Zero Ports”

Session 2 – Smart Shipping & Operations: Chaired by Prof Ying Xie, Cranfield University

  • Prof Alice Larkin, University of Manchester: “Decarbonising shipping: the case for focusing on the existing system”
  • Tuur Killaars, Foreship: “Smart operations, a net zero enabler”
  • Matthew Napleton, Zizo: “How Does Data & Digitalisation Drive Decarbonisation?”

Session 3 – Finance, Insurance & Law: Chaired by Dr Claire Copeland, Durham University

  • Dr Pia Rebello, City St Georges, University of London: “Legal Aspects of Decarbonising City”
  • Helen Barden, North Standard: “Maritime Decarbonisation – the insurer’s perspective”
  • Andrew Southwood, Siemens Financial Services: “Financing the transition”

The Economics of Decarbonization Regulation: The Case of Shipping Efficiency

“Abstract

Measures towards net-zero transition need to ensure the well-functioning of the market. This paper focuses on shipping where the existing environmental regulations lack considerations for the industry’s economic performance. We apply a stochastic frontier analysis to estimate the carbon, production, cost, and allocative efficiencies for 14 major shipping segments and 664 individual vessels. Our findings suggest that carbon and production efficiencies have increased but cost efficiency has decreased from 2021 to 2024. There is scope for the average vessel to reduce its carbon emissions by 31%. Additionally, fuel is underused by 37% and capital is overused by 58%. Technical and operational inefficiencies increase the total cost by 6%, with market price dynamics increasing it by 17%. The results suggest that, without further policy intervention and clear economic incentivisation, there is limited potential for the industry to follow the energy transition pathway.”

 

Shi, Yao and Moutzouris, Ioannis, The Economics of Decarbonisation Regulation: The Case of Shipping Efficiency (March 31, 2025). Available at SSRN: https://ssrn.com/abstract=5205272 or http://dx.doi.org/10.2139/ssrn.5205272

The full report is also accessible via: Page-48_56-CID-Summer-2025-IM-YS-061925.pdf

 

For related publications please see Resources – UK National Clean Maritime Research Hub

Green Investment Under Market Uncertainty: Scrubber Installation in Shipping

“Abstract

In 2020, the International Maritime Organization implemented a limit to the sulphur content emitted by vessels. To comply with it, a vessel should either incur the capital cost to be retrofitted with a scrubber or burn fuels that emit less sulphur but are more expensive. We examine this dilemma by developing a Vector Error Correction Model that links freight rates, fuel prices, and the green investment decision of scrubber installation. The results, across the tanker and dry bulk sectors from 2021 to 2024, suggest that the freight premium of scrubber-fitted vessels positively depends on the spread between very low-and high-sulphur fuel oil prices and negatively on the size of the scrubberfitted fleet. Scrubber investment, in turn, is determined by the past freight premium and the fuel spread. Being the first to investigate the interplay between green shipping investment and price uncertainty, our findings yield significant industry and policy implications.”

 

Moutzouris, Ioannis and Marchese, Malvina and Papapostolou, Nikos C. and Efstathiou, Angelos and Shi, Yao, Green Investment Under Market Uncertainty: Scrubber Installation in Shipping (February 10, 2025). Available at SSRN: https://ssrn.com/abstract=5130549 or http://dx.doi.org/10.2139/ssrn.5130549

The publication is also available via: https://www.bayes-cid.com/pdf/issues/2025-summer/publications/CID-Summer-2025-Scrubber-040325.pdf

For related publications please see Resources – UK National Clean Maritime Research Hub