Revisiting Port Decarbonization for Advancing a Sustainable Maritime Industry: Insights from Bibliometric Review

Abstract

The maritime industry is crucial in mitigating global warming and advancing sustainable maritime development worldwide. As essential nodes in maritime supply chains and key energy hubs, ports must undergo decarbonization to support global sustainability efforts. Research on port decarbonization (PD) has gained increasing attention in recent years, with several reviews revisiting this topic. However, most existing studies have focused on specific aspects such as measures or policies rather than a holistic perspective. This study adopts a comprehensive approach by examining three key perspectives: PD measures, PD facilitation activities, and PD macro-environmental factors. By systematically analyzing 218 articles retrieved from the Scopus database through bibliometric and content analysis, this study identifies trends over time, geographic distribution, key journals, leading authors, prominent themes, research clusters, researched countries, and methodologies. Key findings highlight the following priorities: (i) broadening the focus to include various port types; (ii) more studies on ports in lower-middle-income economies; (iii) promoting cross regional and international research collaboration; (iv) studying alternative fuels and diversified PD measures through theoretical lenses, innovative, practical, and multifaceted perspectives, and within the context of green corridors and global and regional PD efforts; (v) identifying effective governance models, human resources strategies, infrastructure development, and collaboration mechanisms; and (vi) addressing the direct and indirect impacts of political, legal, and macro-environmental factors on PD.

1. Introduction

The maritime industry (shipping and ports) plays a crucial role in mitigating global warming and achieving the ambitious targets of the Paris Agreement and Sustainable Development Goals. The International Maritime Organization (IMO) and its member states are committed to advancing sustainable maritime development worldwide, with the reduction in greenhouse gas (GHG) emissions remaining a critical and urgent priority for both the shipping and port sectors.

In December 2015, a pivotal milestone in addressing climate change was achieved when 196 parties adopted the Paris Agreement (PA), a legally binding international treaty, at the UN Climate Change Conference (COP21). The agreement sets an ambitious goal of limiting the global temperature rise to well below 1.5 °C, serving as a foundation guideline for efforts across all industries, including the maritime sector. Given that over 80% of global merchandise trade by volume is transported by sea [1], the maritime industry plays a crucial role in global trade, while also being a major consumer of energy and a significant source of pollution [2]. Alongside shipping, ports play an equally crucial role [3,4] as essential nodes in the global supply chain [5] and significant hubs of extensive emissions due to the high concentration in fossil fuel consumption [6].

In alignment with the temperature goals of the PA, the IMO adopted the Initial GHG Strategy in 2018 and further reinforced its commitment to combating climate change by adopting the 2023 IMO Strategy on the Reduction of GHG Emissions from Ships. This strategy aims to peak GHG emissions from international shipping as soon as possible and achieve net-zero GHG emissions by or around 2050 [7]. The 2023 IMO Strategy emphasizes the importance of promoting port development initiatives in parallel with activities to reduce GHG emissions from shipping. Such initiatives include providing renewable energy-based ship and shore/onshore power supplies, establishing infrastructure to supply zero or near-zero GHG emission fuels or energy sources, and optimizing the logistic chains, including port operations.

The environmental issues associated with ports have long been a focus of research. Several related concepts have emerged, including sustainable ports, eco-ports, environmental ports, and green ports. Scientific data sources, embracing Scopus, ScienceDirect, Web of Science, and the grey literature contain articles related to these topics dating back to the 1990s [8,9,10]. Although all these concepts prioritize environmental issues [11], “sustainable ports” represent the broadest concept, encompassing the triple bottom line of environmental, economic, and social considerations [12]. In contrast, “green ports” and “eco ports” focus mainly on the environmental or ecological aspects of port operations [11,13]. It should be noted that all these concepts deal with the environment at ports from a broader perspective, including not only air quality, but also noise, water quality, dust, garbage, and land.

Air quality has been a top priority since the 2000s [14]. However, due to their visible harmful impacts on residents and stakeholders in adjacent communities, local air pollutants such as SOx, NOx, PM, and black carbon remain the main concern of port authorities. Meanwhile, reductions in CO₂ and GHG emissions are often considered merely a “nice by-catch” of implemented initiatives [15].

The literature on port decarbonization has expanded significantly in recent years. In addition to numerous reviews on specific activities such as [16,17], there are also several reviews closely related to the subject of this paper, revisiting the state of the art and providing guidance for future research [18,19,20,21,22,23,24,25,26,27]. However, existing reviews rarely provide a comprehensive, up-to-date overview of the literature on port decarbonization due to methodological constraints [18,24,25,27], a lack of direct focus on port decarbonization [19,21], and/or limitations in research scope [20,23]. Most reviews focus solely on measures [20,22,26] or policies [23], which may lead to an incomplete synthesis and hinder valuable suggestions. To address this gap, this study aims to provide a more comprehensive analysis by answering the following questions:

RQ1: What are the foundations of port decarbonization?

RQ2: What is the current status of the port decarbonization literature (volume growth, geographic contribution, influential authors, key journals, mature and emerging themes, research clusters, researched countries, and utilized methodologies)?

RQ3: What are the gaps and future research avenues?

Addressing these questions contributes to the ongoing discourse on port decarbonization by offering a novel and comprehensive analysis that extends beyond specific measures or policies. This approach enables researchers to develop a holistic understanding of how knowledge in this field is systematically structured and provides insights into future research directions. Additionally, the findings support policymakers, port authorities, port operators, and relevant stakeholders in synthesizing port decarbonization practices, from the macro-level to operational measures, thereby facilitating the development of effective and reliable strategies.

This study is structured as follows: Section 1 outlines the research gaps and objectives. Section 2 presents the foundations of port decarbonization, addressing RQ1. Section 3 details the research methodology, while Section 4 discusses the results to answer RQ2 and RQ3. Finally, Section 5 provides the conclusion and the study’s limitations.

2. Foundations of Port Decarbonization

2.1. Definition of Port Decarbonization

Building on the definition of port decarbonization by Alamoush et al. [28] and the United Nations’s definition of offsetting [29], this study adopts and applies the following definition, which directly focuses on reducing carbon emissions at ports.

Port decarbonization (PD) is the process through which a port achieves carbon neutrality. This is accomplished by reducing CO₂ emissions from all port activities, both within and beyond the port’s geographic boundary, to near-zero levels, while any surplus CO₂ should be captured through carbon sinks or sequestration methods.

PD is not only a response to increasing societal pressure on climate issues but also a strategy to gaining competitive advantages and ensuring long-term benefits for ports as part of the greening port initiative [30]. Moreover, like any other process, the decarbonization process is influenced by macro-environmental factors. Therefore, the concepts of the macro-environment in Johnson et al. [31] and competitive advantage in Porter [32] can be adapted to the context of PD, as illustrated in PD’s generic framework (Figure 1). Decarbonization measures are supported by facilitation activities and influenced by PESTEL factors. PESTEL: Johnson et al. [31] introduced six factors in the macro-environment, including political, economic, social, technological, environmental, and legal (PESTEL). Each element is explained in the following sections to support the literature review.

2.2. Port Decarbonization Measures

Emissions are directly correlated to the amount of energy or fuel utilized and the emission factors [33]. Therefore, three main measures can be exploited to reduce emissions: reducing energy consumption; improving emission factors; and implementing carbon capture, utilization, and storage (CCUS) technologies (Figure 2).

This classification enables the systematic organization of existing measures and facilitates the consistent integration of new measures in the future as science and technology advance. Under each of three categories, measures can be further divided into shipside (seaside and ship–port interface) or landside (yard, administration areas, port–land interface). A summary of decarbonization measures together with respective references is provided in Appendix A.

Reducing energy consumption can be achieved through both technical and operational measures. Technical measures aim to enhance engine energy efficiency, reduce resistance forces or unfavorable external factors, minimize and utilize waste energy, and lower the overall energy demand. In contrast, operational measures focus on decreasing engine operation time or improving operational efficiency by optimizing processes and creating an environmentally friendly, efficient, and seamless flow of resources, including ships, cargo-handling equipment (CHE), vehicles, goods, containers, and workforces.

Improving the emission factor primarily involves adopting cleaner fuels and power sources. Consequently, all measures in this category are technical, focusing on electrification, renewable energy, alternative fuels, or hybrid power systems. A prominent solution is the onshore power supply (OPS), also known as cold ironing, where shore-electric power replaces the vessel’s fossil fuel-powered engines while vessels are at berth.

Regarding carbon capture, utilization, and storage (CCUS/CCS), the first commercial CO₂ CCS project, known as Sleipner, was launched in Norway in 1996, and technologies for CO₂ capture and liquefaction are now industrially available. Several initiatives have sought to demonstrate CCS technology on ships, including the CC-Ocean in Japan in 2021 [34] and EverLoNG in 2023, led by a consortium of Germany, the Netherlands, Norway, the UK, and the USA [35]. Ship-based or mobile carbon capture is considered a promising and viable pathway for emission reduction [36]. On the port landside, while CCS projects are being piloted in leading ports such as the Port of Rotterdam to capture CO₂ from the industry activities [37], developing a green buffer zone presents a simpler yet effective solution [22]. With the inclusion of the Copenhagen Malmö Port in the CCS project [38] (the CCS project refers to the Carbon Capture and Storage Project, where the captured CO₂ is stored and distributed to ships that will transport the captured CO₂ to storage in the old oil fields in the North Sea), it is evident that ports can have the potential to serve as hubs for CO₂ storage and distribution in the future.

2.3. Port Decarbonization Facilitation Activities

In the model of competitive advantage, Porter emphasized that primary (value-creating) activities require support from various facilitation activities. Some of these, such as input procurement or technology development, serve specific primary functions, while others, such as governance or human resource management, have broader influence across the entire value chain. Importantly, facilitation activities do not operate in isolation: they reinforce both primary activities and one another. Additionally, information and coalition are also considered facilitation activities [32].

Applying Porter’s perspective in the PD context and based on the existing literature on PD, PD facilitation activities are activities that support PD and can be categorized into five main groups as follows:

Governance, mentioned as “Firm Infrastructure” in Porter’s model, encompasses various activities such as general management, port governance models and planning [23], financial management [39], environmental management systems [40], or energy management systems [41], and reporting and monitoring, among others.

Human Resource Management: Green human resource management is closely linked to the effectiveness of eco-innovations and firms’ environmental performance [42]. Energy management systems, such as ISO 50001 [43], emphasize the importance of having appropriately qualified personnel to carry out sustainability-related activities. In ports, properly training personnel involved in port operations is essential [44]. Additionally, training can be extended to the landside operators (e.g., train and truck drivers) [45] and seaside personnel (e.g., ship crews and port pilots) to enhance their understanding of the operational behaviors and emissions generated by various activities. Effective maritime education and training can significantly reduce ship maneuvering time and emissions at ports by up to 12.5% [46].

Physical and electric infrastructure: The successful implementation of PD is heavily influenced by the quality of infrastructure [47]. For example, to enable ships and land transport vehicles to transition from traditional fossil fuels to cleaner energy sources, ports must develop a supporting infrastructure such as electric charging stations [48,49], alternative fuel tanks, and refueling stations [50]. At both local and national levels, energy infrastructures such as micro grids or smart grids, which can be integrated with the national grid, are expected to play a crucial role in supporting the adoption of renewable energy in ports [51]. Furthermore, infrastructure availability significantly impacts decisions regarding modal shift solutions [52].

Information System, IT infrastructure: An information system that supports data collection, IT infrastructure such as 5G networks [53], and disruptive IT technologies such as the Internet of Things [54], blockchain, and digital twins serve as foundational elements for technology-based decarbonization measures aimed at optimizing operations. For instance, Eom et al. [55] developed a digital twin model to reduce the vessel waiting times near Busan Port.

Collaboration: Collaboration among stakeholders, both vertically and horizontally, is essential for advancing PD initiatives [56,57]. Alamoush [47] emphasized that cooperation across government levels and sectors can facilitate decision-making, mitigate conflicts, and support technology standardization, ultimately enhancing ports’ green transition. Moreover, ports are encouraged to participate in international networks such as the International Association of Ports and Harbors (IAPH), the World Ports Sustainability Program (WPSP), and the European Sea Port Organization (ESPO) to strengthen global collaboration and sustainability efforts.

2.4. Port Decarbonization’s Macro-Environment

The macro-environment represents the overarching external context that influences all industries, sectors, markets, and organizations. It comprises broad environmental factors, including political, economic, social, technological, environmental, and legal aspects (PESTEL) [31]. According to Johnson et al. [31], many of these factors are interdependent; for instance, the political system is closely linked to legal factors [58], while technological advancements are often influenced by political, social, and economic conditions [59].

Several studies have examined decarbonization in the context of macro-environment factors. For instance, Stephenson et al. [60] analyzed the influence of energy cultures on national decarbonization pathways. Rip & Kemp [59] explored technological perspectives on climate change mitigation. Meanwhile, Kuzemko et al. [61] investigated how the domestic political context shapes sustainable transitions in different ways.

In the context of PD, legal factors including policies and regulations have received increasing attention. As summarized in Figure 3, various legal instruments can be categorized based on their level of coerciveness. At the low end of the coerciveness scale, voluntary agreements rely on cooperation between individuals and organizations to achieve their objectives. In contrast, highly coercive regulations impose formal restrictions on activities. Instruments falling within the medium-coerciveness category include corrective fees, charges, or tariffs, which allow polluters to continue undesirable activities but require them to pay fines or taxes [58]. Additionally, electricity pricing serves as a market-based measure, as market value can influence technological innovation in renewable energy [62].

In general, port decarbonization is a broad research area encompassing PD measures, PD facilitation activities, and the PD macro-environment. These three PD elements interact closely with each other. Utilizing existing reviews [20,23,25] but overcoming the inconsistency in the group classification among them, this foundation section lays the groundwork for a comprehensive and integrated review conducted in this study.

3. Materials and Methods

3.1. Methods

To gain insights into the existing literature, a combination of bibliometric and content analysis was employed. Bibliometric analysis, which relies on quantitative methods, offers the advantage of examining the social and structural relationships among various research elements, such as authors, countries, institutions, and topics [64]. Conversely, content analysis provides deeper insights beyond what is typically accessible to regular readers, transforming available information into structured data that retain the potential to address the research questions [65].

In this study, to provide an overview of volume growth, geographic distribution, network research, main authors, key journals, and research themes, bibliometric analysis was conducted using VOS Viewer software (Version 1.6.20) to examine Scopus metadata, including titles, paper sources, author names, year of publication, affiliations, keywords, citations, and references. To increase the precision of the analysis, the careful checking and synchronizing of data (i.e., authors’ names, key words) are performed, checked, and re-checked by researchers. Additionally, to categorize articles and provide insights into research clusters, research countries, and methodology, content analysis was performed on the articles’ full text. The synthesis, visualization, and presentation of findings, mostly based on the respective accumulative total numbers and percentages, were performed using VOS Viewer and Excel.

To avoid bias and enhance the robustness of the findings, in all steps from data collection to data analysis, independent work by individual researchers was first conducted, followed by cross-checking among team members, double-checking by senior researchers, and group discussions where there were disagreements.

3.2. Source for Data Analysis

Various sources can be used for data analysis, including Web of Science (WoS), PubMed, and Scopus [66]. However, Scopus provides broader overall coverage and indexes a greater number of sources compared to WoS and PubMed [19,67]. While it is possible to combine all sources, inconsistencies in statistical indicators, such as citation counts across different databases, may compromise the accuracy of bibliometric analysis. Therefore, Scopus was selected as the primary data source for this study.

3.3. Search and Data Collection

To ensure a comprehensive overview of research on PD, without diverting into broader concepts or exhibiting bias towards specific aspects such as energy, measures, or policy, the following query was used to search within titles, abstracts, and keywords in Scopus on 12 July 2024 and updated on 6 January 2025 for the number of citations.

TITLE-ABS-KEY ((port OR seaport OR “sea port*” OR “harbo*” OR (maritime AND “terminal”)) AND (“zero emission” OR “carbon emission” OR “carbon footprint” OR “GHG emission” OR “greenhouse gas” OR “CO₂” OR “decarboni*” OR “net zero emission” OR “near zero emission” OR “emission control”)).

The data collection and screening process followed the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines [68], as illustrated in Figure 4. This process was conducted with a high level of consensus among researchers regarding the criteria and outcomes.

The initial identification step yielded 5308 documents. A Scopus filter was applied during the screening step using the following criteria:

• Year: Scopus data from the previous year are fully updated by June of the current year. To ensure the reliability of the review, data were limited to the end of 2023;
• Language: English;
• Publication stage: articles in press were excluded;
• Document type: only articles and reviews were included;
• Subject area: all relevant fields within the research scope were considered, including engineering, environmental science, energy, social sciences, computer sciences, mathematics, business, management and accounting, decision sciences, economics, econometrics and finance, and multidisciplinary domains.
• After screening, 3173 documents were excluded.

In the third step of eligibility, the title, abstract, keywords, and content (if necessary) of the remaining 2135 documents were examined. Recognizing that article selection is critical to the validity and reliability of the research, a strict process, as outlined in Section 3.1, was followed. The agreed-upon inclusion and exclusion criteria, as shown in

Table 1. Inclusion and exclusion criteria.

Inclusion	Peer-reviewed articles that have strict methodologies and focus on CO2 reduction (decarbonisation) at ports from operation and management view.
Exclusion	Articles that did not thoroughly discuss the review topic on decarbonisation, such as articles of pure emission inventory, shipping decarbonisation, eco-efficiency assessment, etc.
	Articles focused only on air pollutants such as black carbon, SOx, NOx.
	Measures as engine design and testing, construction engineering.
	Proceeding articles that share repetitive results in included articles.

, were applied. For example, to credit high-quality studies directly involving PD, papers which do not show a clear methodology were removed [69]. To ensure a consistent understanding before proceeding with the full sample of 2135 papers, a pilot screening of twenty articles was conducted. Lastly, to assess the risk of bias and increase the robustness, external researchers were also invited to independently verify the data selection. Although there were certain differences, a high level of agreement was reached on article selection.

After the eligibility check, an additional 1898 documents were removed from the list, resulting in the inclusion of 237 papers—19 reviews and 218 articles. Review papers were not filtered out during the screening phase because some were classified as articles and vice versa. However, consistent with Pham et al. [70], review papers were excluded from the bibliometric analysis to avoid skewed results, as they tend to receive more citations and differ in scope and methodology. Accordingly, only 218 articles were used for bibliometric and content analyses. Nevertheless, to access whether the inclusion of review papers would affect the identification of main authors, a sensitivity analysis was conducted.

4. Results and Discussion

4.1. Volume Growth, Geographic Distribution, and Network

The annual number of research publications on PD reached double digits in 2017. In the past three years alone, 111 articles were published, accounting for more than 50% of all publications to date (Figure 5a). This upward trend highlights the growing academic interest in PD and establishes it as an emerging focal research field. A closer examination of the annual publication trends in the top five territories (Figure 5b) reveals that this growth is strongly influenced by the increasing contributions of Chinese researchers.

Since 2017, there has been a sharp increase in publications, positioning China as the leading country in this research field in terms of both volume and citations. As shown in

Table 2. Top 10 contributors by volume and citation.

Contributors	Number of Documents (Doc.)	Rank	Contributors	Number of Citations (Cit.)
China	92	1	China	2910
United States	21	2	United States	1461
United Kingdom	17	3	United Kingdom	1001
Sweden	13	4	Sweden	769
Taiwan	12	5	Taiwan	645
Italy	11	6	Australia	630
Spain	11	7	Greece	552
Australia	9	8	Spain	543
Greece	9	9	Denmark	368
The Netherlands/Germany	8	10	Germany	350

, other major contributions include the United States, the United Kingdom, and several European countries such as Sweden, Italy, Spain, Greece, the Netherlands, Germany, and Denmark, along with Taiwan and Australia. These regions play a significant role in advancing research on this environmental issue.

The geographic affiliation network mapping of PD articles is also presented in Figure 6, based on the authors’ institutional affiliations. Each country is represented by a circle, with its size reflecting the number of publications associated with that country. Larger circles indicate higher publication volumes. Lines connecting countries represent collaborative relationships in research publications, with thicker lines signifying stronger collaborations (e.g., the higher frequency of co-authored publications) between countries.

A total of 47 contributing territories have been identified; however, the connection network among these entities remains relatively weak. Alongside the increasing number of publications, China has become a central hub in this network, maintaining significant collaboration with the USA, Australia, and the United Kingdom. Notably, many of these connections are driven by collaborations between Chinese researchers affiliated with different institutions. Additionally, Korea has emerged as a key player in this research field, contributing a substantial number of publications. However, no international collaborations involving Korean researchers were recorded in the analyzed studies.

Knowledge sharing and collaboration are necessary for addressing GHG emissions on a global scale [47]. Academic collaboration is considered a key pathway in this effort, and increasing international joint research projects between different regions, especially environmental leading nations and less developed countries, is crucial to accelerate PD efforts by fostering knowledge exchange and contextualized solutions.

4.2. Main Authors

Among the 687 authors of the 218 analyzed articles, the 10 most productive and influential authors are presented in

Table 3. Top 10 main authors. (a) Main authors in 218 articles examined. (b) Main authors in 237 reviews and articles examined.

(a)
Author	Affiliation	Doc	Rank	Author	Affiliation	Cit.
Chen, Jihong	Shenzhen University, Shenzhen, China	7	1	Corbett, James J.	University of Delaware, USA	612
Wang, Wenyuan	Dalian University of Technology, China	6	2	Wang, Haifeng	Newark, USA	532
Peng, Yun	Dalian University of Technology, China	4	3	Winebrake, James J.	Rochester Institute of Technology, USA	532
Wang, Tingsong	Shanghai University, China	4	4	Chen, Jihong	Shenzhen University, China	422
Dai, Lei	Shanghai Jiao Tong University, Shanghai, China	4	5	Styhre, Linda	IVL Swedish Environmental Research Institute, Sweden	373
Hu, Hao	Shanghai Jiao Tong University, Shanghai, China	4	6	Winnes, Hulda	IVL Swedish Environmental Research Institute, Sweden	373
Diaz-ruiz-navamuel, Emma	University of Cantabria, Spain	4	7	Wang, Wenyuan	Dalian University of Technology, China	272
Zhen, Lu	Shanghai University, China	4	8	Giuliano, Genevieve	California State University, USA	206
Teng, Fei	Dalian Maritime University, China	4	9	O’brien, Thomas	University of Southern California, USA	206
Shan, Qihe	Dalian Maritime University, China	4	10	Chang, Ching-Chih	National Cheng Kung University, Taiwan	201
(b)
Author	Affiliation	Doc	Rank	Author	Affiliation	Cit.
Chen, Jihong	Shenzhen University, Shenzhen, China	7	1	Corbett, James J.	University of Delaware, USA	612
Olcer, Aykut	World Maritime University, Sweden	7	2	Wang, Haifeng	Newark, USA	532
Wang, Wenyuan	Dalian University of Technology, China	6	3	Winebrake, James J.	Rochester Institute of Technology, USA	532
Ballini, Fabio	World Maritime University, Sweden	5	4	Olcer, Aykut	World Maritime University, Sweden	461
Peng, Yun	Dalian University of Technology, China	4	5	Chen, Jihong	Shenzhen University, China	422
Alamoush, Anas S.	World Maritime University, Sweden	4	6	Iris, Çağatay	Nanyang Technological University, Singapore	389
Wang, Tingsong	Shanghai University, China	4	7	Lam, Jasmine Siu Lee	Nanyang Technological University, Singapore	389
Dai, Lei	Shanghai Jiao Tong University, Shanghai, China	4	8	Styhre, Linda	Ivl Swedish Environmental Research Institute, Sweden	373
Hu, Hao	Shanghai Jiao Tong University, Shanghai, China	4	9	Winnes, Hulda	Ivl Swedish Environmental Research Institute, Sweden	373
Islam, Samsul	Dalhousie University, Canada	4	10	Wang, Wenyuan	Dalian University of Technology, China	272

a, ranked based on their number of publications and total citations as of January 2025. It is important to note that these two criteria yield different results, as the most-cited authors do not always produce the highest number of documents, and vice versa. Additionally, more established researchers, such as the research group led by Corbett, James J. or Styhre, Linda, tend to accumulate more citations due to their earlier contributions, whereas emerging authors like Chen, Jihong or research groups led by Wang, Wengyuan, may have fewer citations.

Table 3b presents the result of the main author analysis when including 19 review papers in the dataset. This difference arises not only from the nature of review papers, which typically receive more citations, but also from the significant contributions of the research group from the World Maritime University. This group has conducted extensive reviews covering various aspects of port decarbonization, ranging from technical and operational measures to policy discussion, and from shipping to port-related initiatives. A list of review papers is provided in the Supplementary Data (Table S2).

4.3. Key Journals

A total of 218 articles were published in 86 journals. The top ten journals, ranked by the number of publications and citations, are presented in

Table 4. Top main journals on port decarbonization.

Journal	Doc.	Rank	Journal	Cit.
Sustainability	26	1	Transportation Research Part D: Transport and Environment	2242
Transportation Research Part D: Transport and Environment	25	2	Journal of Cleaner Production	1097
Journal of Cleaner Production	22	3	Sustainability	492
Ocean and Coastal Management	9	4	Energy Policy	469
Energies	9	5	Ocean and Coastal Management	400
Journal of Marine Science and Engineering	9	6	Research in Transportation Business and Management	377
Maritime Policy and Management	7	7	Transportation Research Part E: Logistics and Transportation Review	366
Computers and Industrial Engineering	5	8	Transportation Research Part A: Policy and Practice	317
Energy Policy	4	9	Maritime Policy and Management	305
Transportation Research Part E: Logistics and Transportation Review	4	10	Applied Energy	225

. These key journals accounted for 55% of the analyzed articles, highlighting their central role in disseminating research on port decarbonization. Notably, there is a growing tendency to publish in non-maritime journals, indicating that PD is increasingly being recognized as a multidisciplinary issue. To encourage more research in this area, maritime journals should implement incentives such as faster review turnaround times, thereby attracting a greater number of high-quality publications on PD.

4.4. Researched Themes

Using VOS Viewer for the co-occurrence analysis of keywords, key and emerging research themes in PD were identified.

As illustrated in Figure 7, container terminals have been the primary focus of research, with strong associations with key concepts such as carbon emissions, carbon footprint, and carbon emission reduction. However, limited studies have examined cruise terminals, general terminals, and bulk terminals. Future research should expand to these terminal types to identify and adapt best practices across bulk, liquid, Ro-Ro, and multipurpose terminals, contributing to a more comprehensive understanding of port decarbonization. Additionally, given the increasing emphasis on multimodal transport, investigating decarbonization strategies for inland waterway terminals is essential, particularly in regions where inland waterways play a significant role in freight transportation.

Traditional themes in PD studies, ranked by the number of publications, include cold ironing, energy efficiency, optimization, dry ports, renewable energy, and speed reduction. Meanwhile, emerging themes include alternative fuels, berth allocation, carbon tax, multimodal transport, and environmental efficiency, indicating evolving areas of interest in the field.

Although the above analysis identified trends in the research literature, it does not fully capture the overall structure of the research literature. Therefore, content analysis was applied in the following sections to map of the research landscape, identify research gaps, and suggest directions for future studies.

4.5. Research Clusters

This section categorizes the included articles into homogeneous groups, highlighting research subjects along with respective future research areas. Based on content analysis, the 218 Scopus articles were classified into three main clusters: PD measures, PD facilitation activities, and PD macro-environment factors. Figure 8 illustrates these clusters along with the number of studies in each; however, there might be bias and heterogeneity in allocating articles into research clusters due to the overlap of research topics.

4.5.1. PD Measures

In PD measures, the five most frequently studied are cold ironing, renewable energy, berth and quay crane allocation, vehicle or container handling equipment electrification, and alternative fuels (see Figure 9). Among these, alternative fuels have emerged as a key research theme, examined from various perspectives such as bunkering infrastructure [50], impact assessments [71,72], cost–benefit analysis [73], and feasibility evaluation [74]. However, significant research potential remains in exploring other aspects of alternative fuels. Furthermore, the concentration on these five measures suggests substantial opportunities for studying other under-researched operational measures. Notably, no academic research has yet addressed drone-based deliveries at ports, or carbon capture and storage technologies. Carbon capture devices and carbon-captured power plants have been only briefly discussed in three articles [75,76,77], primarily in the context of distributed energy management.

In the future, rather than reiterating research on conventional measures such as cold ironing, future studies should prioritize underexplored strategies, including berth allocation, gate lane allocation, truck sharing, truck appointment systems, and empty container repositioning. Together with traditional strategies as multimodal transport, infrastructure development, truck sharing [78], truck appointment systems [79], buffer stack [80], chassis exchange terminal systems [80], and containers on barge [81] are solutions for solving truck congestion at ports, contributing to emission reduction at landside. There should be more empirical research on these measures. Additionally, a range of energy-saving measures in Appendix A, such as green buildings, green procurement, and emerging technologies like drone-based delivery and carbon capture should be investigated in the future.

For well-researched decarbonization measures, innovative empirical studies are needed. For instance, in the case of alternative fuels like ammonia, there were studies on ammonia’s safety in the bunkering process [82], an efficiency analysis of ammonia-integrated systems [83], risk assessments [84], and compatibility with dual-fuel marine diesel engines [85]. Nevertheless, empirical validation in real-world settings remains limited. Further, risk assessment and mitigation strategies should be expanded to consider extreme events such as earthquakes and tsunamis, given their increasing frequency and severity. Beyond technological maturity, future research may also use the lens of innovation diffusion to offer comprehensive strategies for accelerating alternative fuels’ adoption, including effective communication channels, regulatory preparedness, and infrastructure development, among others. Comparative analyses of alternative fuels have been widely conducted by numerous researchers such as [86,87,88]. Nevertheless, selecting an optimal alternative fuel is a multifaceted challenge, involving factors such as supply chain availability, technological maturity, infrastructure availability, and economic feasibility. Therefore, developing an extensive evaluation framework is a promising research direction. The model may incorporate moderating factors such as region variation. Finally, alternative fuels and shore power should not be considered as isolated decarbonization solutions. Future studies should examine their integration within broader green corridor shipping initiatives, ensuring alignment with regional and international sustainability efforts.

Moreover, future research should re-evaluate existing measures from unconventional perspectives, offering critical insights for a more comprehensive understanding. For example, applying life cycle analysis (LCA) to cargo-handling equipment (CHE) electrification. The authors of [89] (p. 554) argued that “The transition from diesel to electric handling equipment is a step forward, although from the LCA perspective, ‘zero emission’ operations are impossible to achieve”. A similar approach could be extended to alternative fuels, examining their cooling effects, potential trade-offs, and crowding-out effects among different PD measures.

Among the decarbonization measures analyzed in relation to decarbonization policies, cold ironing is the most frequently examined (13 of 19 articles). It has been considered in various policy contexts, including subsidy policies [90], environmental incentives [91], energy pricing [92], and carbon trading schemes [93]. Other policy-related topics include modal shifts and subsidy policies [94]; concession contracts [95]; the cooperative optimization of shore power and berth allocation [96]; berth allocation and quay crane assignment under environmental taxation [97]; and speed reduction strategies in response to regulations impacts and fuel taxation policies [98]. Many policies have been designed or assessed with a narrow focus on the emission reduction effectiveness of a specific measure, while overlooking their broader environmental, economic, and social impacts. Future research should adopt a more integrated approach to better understand the multifaceted implications of policies.

In the measure facilitation sub-cluster, most research focused on micro-grids and smart-grids in supporting renewable energy or fuel cells [99,100]. Other research explores operational coordination practices, such as truck appointment systems [79], truck-sharing programs [78], and empty container repositioning [101]. Many research opportunities remain and are discussed more in Section 4.5.2.

4.5.2. PD Facilitation Activities

Within this research cluster, governance, particularly emission inventory or efficiency-based strategies; energy management systems, electric infrastructure such as micro-grids, smart-grids, and energy storage systems; and collaboration gain the most attention. Research on other topics such as human resources, physical infrastructure, decision supporting tools, or management systems is still very limited (see Figure 10).

(a)

Governance

This is the largest sub-group under the PD facilitation activities cluster. However, it is worth wondering about whether we are reinventing the wheel [24] when many articles fall into the topic of emission inventory or emission efficiency.

Various articles proposed PD strategies based on the calculation and analysis of emission inventories [102,103,104,105]. This approach helps authors to identify major emission sources, suggest mitigation measures, and estimate their potential impact. However, relying solely on emission inventories using a quantitative approach with secondary data keeps most of articles in this sub-group from intensely assessing the feasibility of recommendations. Taking further steps to strengthen suggestions or developing decision-support tools is a pathway for future research. For example, in addition to the inventory results, Styhre et al. [106] considered the frequency of a ship’s return to a port when evaluating potential solutions. In another illustration, Mamatok et al. [107] developed system dynamics modeling to incorporate the operational complexities of ports, such as throughput fluctuations. Nevertheless, making a decarbonization strategy is a complex problem. Future research could further refine existing frameworks to account for realistic matters, including conflicting stakeholder interests and intricate datasets [108]. Moreover, many emission inventories focus on specific areas, leading to strategies derived from emissions analysis that are often tailored to particular ports or terminals rather than a national or global perspective. This leaves space for future research. To date, no global port emission inventory exists [24]. PD is a global challenge, requiring solutions at an international scale [109]; establishing a globally standardized methodology for inventory calculations is necessary to facilitate cross-country comparisons. Such an approach would help identify the best practices and enable the adaptation of successful strategies across different ports.

Another common sub-group within governance comprises studies that propose strategies based on environmental efficiency evaluation [110,111,112], using Data Envelopment Analysis (DEA) and its variants, such as the slacks-based measure. A limitation of these articles is the lack of the deep need to fully explain the underlying causes of efficiency differences, thereby reducing the persuasiveness of the proposed measures. Future research in this cluster may take advantage of mixed methods to produce more insightful solutions.

The port decarbonization process is influenced by certain drivers [15,113] and faces specific challenges [114], barriers [115], and risks [116]. Although each port in each region has its own characteristics, sharing lessons and learning, for example the management system [41], from early adopters who have successfully implemented PD is essential for accelerating global PD.

Moreover, governance plays a pivotal role in any transformation process; however, research on this aspect of PD remains limited. Future research can examine PD from various aspects of firm governance, including but not limited to leadership, organizational culture, organizational learning, management strategies, finance, and accounting. For instance, it is essential to examine how to sustainably leverage financial organizations and NGOs in supporting decarbonization efforts, particularly in lower-middle-income economies. Monios et al. [117] highlighted the evolving nature of port governance in response to climate change. Future empirical work should analyze and compare how governance changes vary across different governance models (e.g., public, private, tool, service) and various national contexts.

(b)

Human resources

Human resource management has been largely underexplored. Among the 218 analyzed articles, only Paulauskas et al. [46] examined the impact of human resources on PD. It was highlighted that enhancing the competency of ships’ crews and port pilots can reduce emissions from ships at port areas by up to 12.5%.

It is essential for future research to explore how PD will impact human resource demand, job descriptions, and job specifications. A comprehensive understanding of these changes will enable the timely adjustment in education and training, ensuring a smooth transition for the workforce. In the latest update, there were studies on seafarers in the age of greening shipping [118], highlighting skills and competencies for balancing environmental objectives with operational safety [119]. There is a need for future empirical studies to validate the skills framework suggested in existing studies and assess the relevance and importance of these specific seafarers’ competencies [120], verifying their effectiveness in emission reduction. Moreover, future research may look at other groups such as on-shore working groups or workers in the logistics sector for better coordination. Additionally, other aspects of human resource management, such as performance evaluation, should be explored.

(c)

Physical and electric infrastructure

With the growing interest in renewable energy, self-sufficient energy hubs, and the increasing electrification of energy intensive-units, energy management systems, including micro-grids, smart-grids, and energy storage systems, have emerged as prominent research topics [121,122,123]. These articles focused on optimizing energy management, from dispatch or distribution to storage and system design, to achieve cost-efficient, low-emission, and reliable port energy operations. Notably, renewable energy is often incorporated into research on energy management systems. However, studies specifically addressing physical infrastructure remain limited. As alternative fuels are increasingly adopted, further studies are needed to address the infrastructure and facilities required for effective storage, safe bunkering, and rapid emergency response in the event of an incident.

(d)

Information systems and IT infrastructure

While digitalization can directly reduce GHG emissions through improving operational efficiency [55], information systems in general can also support the PD process. For example, the emission inventory, one of the pivotal steps of PD, is also strongly influenced by information quality. Cammin et al. [124] found that data confidentiality and weak information systems are major obstacles that hinder the creation of high-quality emission inventories and generate extra costs for ports.

(e)

Collaboration

Collaboration is believed to be a critical enabler of effective decarbonization strategies. The topics of coordination, collaboration, cooperation, and integration have been explored not only in research on decarbonization measures such as truck sharing and container repositioning, which were mentioned in Section 4.5.1, but also in policy-related studies, or other facilitation activities. To understand the mechanism and impacts of collaboration, many models have been developed, namely in conjunction with the subsidy and carbon tax mechanisms [56,125], market-based policies [126], governance [57,127], electrical management systems [128], and energy infrastructure and data management [129].

However, similar to previous research topics, there is a lack of empirical studies on collaboration. Future empirical research is needed to validate the impact. Less-researched topics, such as collaborative planning between ports and cities for the development of renewable energy strategies, are also recommended. Green corridors are increasingly recognized as a means to promote the adoption of alternative fuel and shore power. Future studies should address their broader impacts, including effects on local communities and regional planning [130] and their long-term implications for environmental sustainability and economic factors [131]. Additionally, future research should explore legal frameworks, key drivers of green corridor initiatives, the restructuring of shipping alliances, and the resulting impacts on global shipping networks and green corridors.

4.5.3. Macro-Environment Factors

There is limited recorded research that analyzes macro-environmental factors in relation to PD practices. In their descriptive study, Damman and Steen [127] concluded that the local context, market conditions, and social networks can influence the sustainability transition of a port. Similarly, Christodoulou and Cullinane [41] conducted a PESTEL analysis on two ports in Northern Europe to identify actors that have a positive or negative impact on the adoption of a port energy management plan.

Apart from the two studies mentioned above, the remaining 31 articles deal with legal factors, including policies and regulations. Figure 11 provides a breakdown of the research on port decarbonization policies.

The majority of studies on decarbonization policies (64%) analyzed them in relation to specific decarbonization measures, as discussed in Section 4.5.1. An additional 10% explored policies in the context of competition or cooperation among ports, highlighted in Section 4.5.2. The remaining 26% focused on evaluating specific policies such as ports’ attitudes towards regulations [109], comparisons between unilateral and uniform maritime emission regulations [132], or modeling interactions among government, ports, ships, and port residents under different policy scenarios like the tripartite evolutionary game model [133,134].

Beyond policy considerations, future research should investigate the broader macro-environment factors influencing port decarbonization, particularly political and social dimensions. Lam and Notteboom [63] examined green port policies and highlighted the differences between European and Asian countries; however, their study primarily focused on port governance. Future research should incorporate social and economic aspects, including cost–benefit assessments, to provide a more comprehensive understanding of the overall impact of decarbonization policies [135]. Recognizing that political systems are closely linked to policy design and public tools [58,136], further investigation is needed into how different political systems influence preferred PD policies.

In the context of policy research, aligning with the future of alternative fuels and renewable energy, future studies should focus on policy mechanisms that facilitate their adoption and implementation. Given the evolving role of ports in energy generation, storage, and distribution, future research should also explore the potential for ports to function as energy hubs and the policy frameworks necessary to support this transition.

Generally, a comprehensive review of the port decarbonization (PD) literature reveals that no research to date has fully examined all three key clusters: macro-environment, facilitation, and measures. This gap presents a promising avenue for future research to explore how changes in PD macro-environmental factors influence PD facilitation activities, thereby indirectly advancing PD measures and overall PD achievements.

4.6. Researched Countries

A total of 57 territories were examined in the analyzed studies, as illustrated in Figure 12. The number at each country indicates how many times it was used as a case study in the reviewed publications. Appendix B provides a breakdown of the number of papers per case study.

China emerged as the most extensively researched country, followed by the United States and the Netherlands. This is unsurprising, given that China leads in research outputs in this field, while the United States or the Netherlands are traditionally at the forefront of environmental initiatives. Their ports, such as the Ports of Los Angeles, Long Beach, and Port of Rotterdam, serve as benchmarks and sources of valuable lessons. Other frequently studied countries include Spain, Italy, Sweden, the United Kingdom, Germany, Greece, and Taiwan. Notably, the Port of Singapore contributed only two studies, despite its reputation for both operational and environmental efficiency, as highlighted by Dong et al. [137].

Figure 13a categorizes the researched countries by region, revealing that Europe accounts for the largest share (54.4%), followed by Asia, primarily focused on China, Taiwan, Korea, and Japan, while research on other Asian countries remains limited. North America ranks third, whereas studies in Africa, South America, and Oceania are notably scarce. This finding aligns with findings from recent reviews [20,24]. Additionally, when classifying the researched countries by income based on the World Bank’s country classification 2024, it becomes evident that lower-middle-income economies receive minimal attention in PD research, as illustrated in Figure 13b.

The over-concentration of research in specific geographic regions may limit the generalizability of findings and hinder evidence-based strategies for global PD. Future research should focus on underrepresented areas, particularly ports in Africa, South America, Oceania, and certain parts of Asia, especially those in lower-middle-income economies. These ports often face greater challenges in the transition to decarbonization due to limited financial and technological resources.

4.7. Researched Methodologies

Regarding methodologies, studies are systematically divided into quantitative (using secondary data or primary data), pure simulation (using hypothetical data), qualitative, and mixed methods, with the number of papers per category shown in Figure 14.

Current research on PD primarily relies on quantitative approaches, using secondary data or simulations. Notably, simulations that do not reference specific case studies are predominantly used in optimization studies related to berth, quay crane, or yard crane allocation. There is a lack of empirical studies employing qualitative methods, integrating secondary and primary data, or using mixed methods. Addressing this gap would make the PD literature more insightful and practical.

For instance, in evaluating a port’s emission efficiency, a mixed methods approach would provide a more profound understanding about the best case study. In macro-environment-related articles, incorporating qualitative and primary data collection could also offer a holistic perspective on the societal and economic impacts of PD policies.

Future research on decarbonization strategies should prioritize generating comprehensive and actionable insights for policymakers and port operators. Mixed methods approaches can be particularly valuable in developing tailored and scalable solutions. Additionally, integrating advanced analytical tools, such as machine learning and big data, can significantly enhance the development of innovative and data-driven decarbonization strategies.

5. Conclusions

In conclusion, GHG emission reduction has garnered increasing attention in recent years. This study provides a holistic overview based on foundational elements, including PD measures, PD facilitation activities, and PD macro-environment factors. Through a bibliometric and content analysis of 218 articles retrieved from the Scopus database, we systematically mapped the PD research landscape, identified existing gaps, and proposed future research directions.

The main outcomes are highlighted:

(1)

There has been a sharp increase in the PD literature since 2017. To date, this research field has involved 687 authors from 47 countries worldwide. The majority of contributions originate from China, the USA, the United Kingdom, and European countries, along with Taiwan and Australia, while Korea has emerged as a key player. As a result, key authors and research groups are predominantly based in these countries. There are highly cited papers from established research groups, such as those led by Corbett, James J.; Styhre, Linda; and Giuliano, Genevieve. Additionally, there are increasing publications from strong research groups such as Chen, Jihong, Wang, Wengyuan, and Olcer, Aykut. However, international collaboration among researchers remains limited, highlighting the need for greater cooperation between institutions across regions. Furthermore, the metadata of 218 articles spans 86 journal sources. Notably, among the top ten journals, non-maritime journals constitute the majority.

(2)

The most dominant keyword over the past decade, “carbon emissions”, is strongly linked to “container terminals”, “cold ironing”, and “green ports”, highlighting that other types of terminals and decarbonization measures remain underexplored. Meanwhile, “emission reduction”, “alternative fuels”, “berth allocation”, “carbon tax”, and “multimodal transport” are emerging topics.

(3)

The research clusters are consistently based on the PD’s generic framework, embracing the following:

• PD measures represent the primary research cluster. The five most frequently studied measures include cold ironing, renewable energy, berth and quay crane allocation, vehicle or CHE electrification, and alternative fuels. In contrast, carbon capture and storage have received relatively minimal research attention.
• PD facilitation activities constitute the second-largest research cluster. Within this category, the emission inventory-based strategy takes the highest attention, followed by physical and electronic infrastructure, driven by growing interest in energy management systems. However, research on IT infrastructure and human resource management remains extremely limited.
• The PD macro-environment factor cluster includes articles focusing on legal factors, particularly policies and regulations. Political, economic, social, technological, and environmental factors remain underexplored areas.

(4)

The analysis results of researched countries by geographic region and by income reveal that lower-middle-income economies receive minimal attention in PD research.

(5)

Current research on port decarbonization (PD) primarily employs quantitative methodologies, often utilizing secondary data or simulations. There is a notable lack of empirical research incorporating qualitative approaches, integrating secondary and primary data, or utilizing mixed methods.

From these findings, the following future research directions should be considered:

(1)

Greater academic attention is required for emerging topics such as “emission reduction”, “alternative fuels”, “berth allocation”, “carbon tax”, and “multimodal transport”.

(2)

A broader range of port types should be explored to identify and adopt best practices across bulk, liquid, Ro-Ro, and multipurpose terminals. Given the growing emphasis on multimodal transport, investing in decarbonization strategies for inland waterway terminals is essential.

(3)

Decarbonization at ports in lower-middle-income economies across Africa, South America, Oceania, and certain parts of Asia should be examined in consideration of financial and technological resources.

(4)

Encouraging collaborative research between authors from developed and developing countries, as well as across different regions, could accelerate decarbonization efforts by fostering knowledge exchange and developing context-specific solutions.

(5)

Regarding PD measures, alternative fuels and shore power should be examined within the broader context of green corridor shipping initiatives to ensure alignment with regional and international sustainability efforts. Theoretical lenses such as the diffusion of innovation and the LCA approach should be included in studies of PD measures. Furthermore, a range of energy saving measures, including newly invested measures such as drone-based delivery and carbon capture measures should be prioritized for future research.

(6)

In terms of PD facilitation activities, further studies should address the following: (i) physical infrastructure to support the expanding implementation of alternative fuels; (ii) digitalization and IT infrastructure for optimizing port operations; (iii) PD from a governance perspective, including leadership, organizational culture, organizational learning, management strategies, and financial mechanisms, as well as how governance changes across different models and diverse national contexts; (iii) human resource management and necessary curriculum adjustments to effectively implement PD initiatives; (iv) the impact of collaboration on different decarbonization measures, policies, and strategies, as well as its integration with other facilitation activities; (v) green corridors and their broad impacts on local communities, regional planning, environmental sustainability, and economic factors; and (vi) legal frameworks and key drivers of green corridor initiatives and the impacts of restructuring of shipping alliances on global shipping networks and green corridors.

(7)

Concerning PD macro-environment factors, future research should investigate the political and social factors influencing PD, and how different political systems shape preferred PD policies. Regarding the legal factors, future studies should focus on policies and legal frameworks that facilitate the following: (i) the adoption and implementation of alternative fuels and renewable energy, (ii) the role of ports as energy hubs for generation, storage, and distribution, and (iii) the use of carbon taxes as a market-based measure to incentivize PD.

(8)

Concerning the relationship between three perspectives, further studies could investigate how changes in PD macro-environmental factors influence PD facilitation activities, thereby indirectly advancing PD measures and overall PD achievements.

(9)

Relating to methodologies, future empirical studies should consider qualitative methods and primary data to offer a comprehensive understanding of the societal and economic impacts of PD. Additionally, future research should focus on providing actionable insights for policymakers and port operators, using mixed method approaches to develop tailored, scalable solutions, and incorporating advanced tools like machine learning and big data to enhance innovation in decarbonization strategies.

As with other studies, this research is not without limitations. The research encountered certain constraints in data collection and analysis. While we present a broad synthesis of decarbonization measures, facilitation activities, and policies, we do not conduct in-depth analyses of individual measures, as doing so would have significantly expanded the scope of the paper. Furthermore, we may have overlooked insights from related fields, such as smart ports, green ports, and eco-ports. This expansion may provide a diachronic approach; however, it would also increase the number of studies included, potentially diluting critical insights and limiting the depth of the evaluation of the existing research landscape. Moreover, we excluded the grey literature, such as technical reports and conference proceedings. Lastly, although we have tried our best to minimize bias, reduce missing data, and increase the confidence of data and analysis, these matters may remain. This is partly due to human errors and the fact that external checks were conducted on a random sample only. Furthermore, interpretations of the exclusion criteria may still differ slightly among researchers.

To the best of our knowledge, this is a pioneering study to develop a comprehensive framework that synthesizes all aspects of PD. This approach provides a more holistic perspective on the existing literature. As a result, this study serves as a one-stop reference for researchers, policymakers, port authorities, and port operators, enabling them to navigate the complexities of decarbonization efforts for advancing a sustainable global maritime industry.