Ports play a crucial role in cities’ and urban areas’ economic, environmental, and social sustainability, with the impact they have extending well beyond the waterfront. They are vital nodes in the urban logistics network, enabling the movement of products and commodities into and out of towns and cities. Ports considerably boost urban economies by creating employment opportunities, bolstering trade-related industries, and increasing local tax revenues. According to a plethora of research that highlighted ports’ role in cities and urban areas, including energy transition and decarbonisation, e.g., Refs. ^[1][2][3][4][1,2,3,4], ports play a vital role in freight transportation, serving as crucial transfer and consolidation nodes that optimize supply chains and reduce transportation costs for urban businesses. Additionally, the strategic location and role of ports in integrating global supply chains makes them indispensable elements of urban logistics, ensuring that cities remain economically robust and well-connected to the international markets.

Ports are entering a new stage that requires them to expand beyond their typical role in cargo handling and value-added logistics. This is attributed to pressing environmental concerns, particularly the decarbonisation and energy transition of the transport sector, including the associated strict regulations and scrutiny. Maritime transport is dependent on fossil fuels [5]. Thus, its decarbonisation, in line with Paris Agreement goal to limit global warming, is at the top of countries’ and industries’ agenda, considering that not meeting the decarbonisation goal intensifies the climate change threats to the environment and humanity [6]. This is manifested by provisions, directives, and guidelines from intergovernmental and non-governmental organisations, e.g., International Maritime Organisation (IMO) ^{[7][8][9][10]}[7,8,9,10], International Association of Ports and Harbours (IAPH), and the World Port Sustainability Programme (WPSP) ^[11][12][13][11,12,13], as well as the European Commission’s Climate Law, the European Seaport Organisation (ESPO) [14], and the Association for Waterborne Transport Infrastructure (PIANC) [15].

Today, ports are urged to decarbonise more than ever due to several fundamental drivers and motivations. Decarbonisation meets the global and regional regulations (compliance) [16], e.g., Paris Agreement, European Union (EU) green deal, and climate law, including the Onshore Power Supply (OPS), alternative fuels bunkering (Directive 2014/94/EU), and Emission Trading Scheme (EU ETS). Similarly, taking environmental actions reduces the pressure from surrounding communities, NGOs, logistics chains (customers, shippers, consignees, liners, and carriers), insurers, politicians, and city officials ^[17][18][19][17,18,19]. It also greens the port and expands its sustainable performance ^[20][21][20,21], which ultimately improve economic competitiveness [22]. Furthermore, it is argued that decarbonisation contributes to meeting the ports’ corporate social responsibility (CSR) ^[23][24][23,24], improves energy efficiency and security (through renewable energy and energy efficiency) [25], and decreases energy costs [26]. These in turn fortify the ports’ green image and attract young and talented professionals who meet the requirements of the technological revolution. Also, port decarbonisation contributes to achievement of the environmental dimensions of the United Nations Sustainable Development Goals (UN SDGs, 2030 agenda), i.e., Goal 7 (access to renewable energy), Goal 12 (sustainable consumption and production), and Goal 13 (actions to mitigate climate change), among others [27]. Similarly, port decarbonisation strengthens the commitment to IMO’s GHG strategy for shipping decarbonisation ^[10][28][10,28].

Several studies have addressed port decarbonisation (GHG emissions), though in a fragmented way and from different perspectives, i.e., technical [29], operational [30], management and policies [31], energy efficiency [32], ship side operations ^[19][26][19,26]), and land transport [33]. Additionally, numerous reviews have focused on port decarbonisation and energy efficiency, resulting in a collection of various measures and solution including policies ^{[28][34][35][36][37][38]}[28,34,35,36,37,38].

The problem, from a practice and technical perspective, is that, despite the visible impact of climate change and pressing regulations, industries, including shipping ^[39][40][39,40], ports ^[34][36][38][34,36,38] and land transport [41], have not yet achieved their target to decarbonise and reach zero emissions. Maritime transport is thus moving at a snail’s pace in the decarbonisation process, although its share in global GHG emissions is high, i.e., ships emit around 3% [40] and ports around 2% [5] of global CO₂ emissions. This slow uptake of decarbonisation technologies and measures, exacerbated by the expected increase in freight transport and its emissions ^[40][42][40,42], is attributed to various barriers that restrict adoption of technologies, i.e., organizational, institutional, economic, political, regulatory, managerial, and technical barriers, among others ^[37][43][44][37,43,44]. Academically, a broad overview of port decarbonisation studies indicates that barriers were referred to generically and no specific study investigated the barriers from a port perspective, in particular decarbonisation and energy transition. No study has defined port decarbonisation and linked it to the Paris Agreement. Another academic gap is that, despite the barriers problem, no study thus far has provided sound solutions and suggestions to break down and mitigate their effects. Based on the identified problems and gaps, while considering the environmental pressure on ports, this researchtudy, via a thorough literature review, aims to define the port decarbonisation concept and pathways and provide unified categorisation of the barriers and solutions to port decarbonisation while identifying opportunities arising for ports from riding the track of decarbonisation.

2. Decarbonisation Concept and Definitions

The primary greenhouse gases (GHGs) that have impact on the climate are water vapor, carbon dioxide (CO₂), nitrous oxide (N₂O), methane (CH₄), and ozone (O₃). Their increase intensifies the greenhouse effect that warms the surface of the troposphere. When infrared radiation is emitted by the Earth’s surface, GHGs absorb and re-emit them back to earth rather than permitting them to pass through into space. Thus, global warming occurs, which trigger climate hazards that cause severe impacts, e.g., warming, precipitation, floods, drought, heatwaves, fires, sea level rise, storms, diseases such as global cholera, and water supply contamination ^[45][46]. These hazards influence six key aspects of human life, i.e., health, food, water, infrastructure, economy, and security ^[45][46]. To stop the future climate change impacts, the Paris Agreement aims to limit global warming, preferably to 1.5 °C and significantly below 2 °C by 2100, compared to the pre-industrial level ^[46][47]. This requires global sectors to decarbonise on average by 2050 ^[47][48]. In the Paris Agreement, COP26, more than 140 countries, covering 90% of global GHG emissions, put forward the net zero goals (climate neutral) by 2050, with ambitious commitments by 2030 ^[46][48][47,49]. The commitment is to be achieved through short- and long-term sustainability measures, although there are slightly different timeframes and benchmarks between countries and sectors as they start from different baselines. Because all sectors need to decarbonise by 2050, the 2050 benchmarks are similar across all countries, whereas the 2030 benchmarks provide an interim step on the pathway towards 2050 ^[47][48]. This means that GHG emissions must be reduced considerably by 2030 (low and near zero), while achieving net zero emissions (climate neutral) is by 2040 or 2050 at latest. In this sense, decarbonisation is the achievement of net zero GHG emissions by 2050. Net zero (In net zero, actors need to reduce their absolute GHG emissions across its whole supply chain (i.e., stakeholders in scope 3, such as suppliers, investments, employees), directly or indirectly, in order to support the target to limit global temperature increases to 1.5 °C), as underlined by the Paris Agreement, is to “achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century (2050)” ^[49][50]. In other words, to reach net zero, countries need to reduce GHG emissions as much as possible by mitigation measures, and the surplus emissions should be balanced by removals, such as removal of CO₂ emissions from the atmosphere by carbon sequestration processes. Decarbonisation has become a worldwide imperative and a top priority for governments, businesses, and society as a whole due to its vital role in reducing global warming. Mitigation measures include the switch from fossil fuels such as coal, natural gas, or oil to carbon free renewable energy technologies and energy sources such as low carbon fuels. The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) provided warnings with regard to the increase of anthropogenic CO₂ emissions; the report called for urgent global actions to combat climate change ^[50][51]. According to the report, it is evident that other GHGs and air pollutants may impact the climate, but carbon dioxide (CO₂) remains the primary cause of global warming, and thus carbon emission is a worldwide issue in the twenty-first century and should be restrained and controlled. On this basis, the term used to achieve net zero carbon emissions is “carbon neutral”. Derived from ^[51][52][52,53], carbon neutrality is achieved when a polluter’s net contribution to global CO₂ emissions is zero, meaning that complete decarbonisation is reached, mainly with direct or indirect reduction of CO₂. In other words, the CO₂ emissions from the polluter’s activities need to be fully compensated by reducing the CO₂ or removals entirely claimed by polluter, irrespective of the of the time period or the relative magnitude of emissions and removals involved. The term carbon offset is also used in climate policy which refers to a unit of CO₂e (Carbon dioxide equivalent (CO₂e): A way to place emissions of various radiative forcing agents on a common footing by accounting for their effect on the climate. It describes, for a given mixture and amount GHGs, the amount of CO₂ that would have the same global warming ability, when measured over a specified time period”. Thus the CO₂e is the GHG emissions assuming a 100-year global warming potential ^[51][52]) emissions that is reduced, avoided, or sequestered to compensate for emissions occurring elsewhere. Additionally, “carbon positive” can be defined as “residual emissions will need to be offset or inset, i.e., cross-sectoral offsetting, or insetting in the same sector”, while “carbon negative” can be defined as “net reduction in CO₂ through generation of surplus of renewable energy or carbon sequestration” ^[52][53]. Based on this section discussion and a comprehensive literature review, this line of research has built definitions for decarbonisation of maritime transport (shipping and ports), which are as follows:

• Decarbonisation is defined in this researchtudy as achievement of net zero CO₂ emission by 2050 by using mitigation measures and/or through the balance of surplus emissions by removal (e.g., carbon sinks and sequestration). “Mitigation measures” indicates the switch from fossil fuels such as coal, natural gas, or oil to carbon free renewable energy technologies and energy sources such as low carbon fuels.
• Maritime transport decarbonisation can be defined as the process of eliminating ships’ CO₂ and other GHG emissions through mitigation measures or balance of surplus emissions by removal leading eventually to net zero CO₂ emission by 2050. The IMO, based on the recently adopted GHG strategy [10], pledged to reduce the total annual GHG emissions from international shipping by at least 20%, striving for 30%, by 2030, and 70%, striving for 80%, by 2040, respectively, compared to 2008; that is to say that the industry aims to reach net zero emissions by or around, i.e., close to, 2050.

• Port Decarbonisation
• is defined as the utilization of mitigation measures (technical and operational emission reduction measures) to reduce, neutralise, and offset CO₂ emissions from various port emission sources (port operation, ships, and land transport), while surplus CO₂ emissions are offset by sinks or sequestration; that is to say that the industry aims to reach net zero emissions by 2050 in line with Article 2 of Paris Agreement.

Technical and Operational Measures for Port Decarbonisation

Measures to decarbonise emission sources in the port (GHG emission reduction) have been reviewed and analysed, e.g., review of the tools for port sustainability [21], port energy efficiency measures [34], European ports’ energy efficiency best practices [35], ports’ technical and operational measures to reduce GHG emissions [36], port polices for decarbonisation [37], ports’ measures for shipping decarbonisation [28], and solutions for planning the zero emission port through energy efficiency [38]. As can be seen in Table 1, there are various decarbonisation measures. The list of port decarbonisation measures is as per the categorisation in [36], which includes measures to decarbonise port operation (i.e., cargo handling equipment, e.g., cranes, derricks, forklifts, port trucks, and vehicles, etc.) and infrastructure and other marine service activities (e.g., tugs, tow and pilot boats). For in-depth details, readers are instructed to read the same study [36]. Additionally, there are measures ports can take up to reduce carbon emissions from land transport, as well as from ships at the ship-port interface. It should be noted that decarbonization measures are not a silver bullet to achieve zero emission ports. However, they can assist in the transition through combinations of measures in order to achieve the maximum abatement potential. In addition, the measures have challenges (technical issues, costs, and varying abatement potential, space requirement (high density of alternative fuels), high upfront cost, environmental benefits (the case of electrification based on fossil fuels grids), life cycle issues, methane and CO₂ slip, the long lead time for infrastructure upgrading and renovations, etc.). Consequently, ports should carefully evaluate the measures and consider the advantages and disadvantages through feasibility and cost benefit ratio studies.

3. Barriers to Decarbonisation

Although ports can reach their climate targets due to availability of technologies (see Table 1), they are lagging behind due to different barriers that result in an implementation gap. An implementation gap, or paradox, appears once what is expected (objective of a policy) and the outcome are compared and the result leads to the observation that there is an implementation gap (failure) ^[56][57]. Sorrell et al. described the barriers as inhibitors that restrain investments in environmentally and economically efficient technologies and measures ^[57][58][58,59]. Barriers influence proper implementation despite existing stringent requirements (regulations). Most of the barriers, particularly to energy efficiency, have been investigated from the perspective of neoclassical economic theory, such as agency theory and contract theory, e.g., Refs. ^[57][58][59][58,59,60], though there were some investigations from the perspective of shipping energy efficiency ^[43][60][61][43,61,62], including decarbonisation ^[62][63]. Sorrell et al. built a framework to investigate the barriers, i.e., organisational (power and culture), behavioural (bounded rationality, form of information, credibility and trust, inertia, values and priority accorded), economic market failures (principal agent problem, split incentives, moral hazard, imperfect/asymmetric information), and non-market barriers (market heterogeneity, hidden cost, access to capital and risks) ^[57][58][58,59]. Thus, this researchtudy has adopted these categories to investigate the barriers to port decarbonisation, in addition to including some new categories identified in the researchview (see Figure 1). In the following section, thwe researchers provide a systematic analysis of barriers (Figure 1) from the perspective of port decarbonisation following the framework of Sorrell et al. ^[57][58][58,59] and augmented by research that has studied barriers from theory and practice, i.e., ^{[59][63][64][65][66][67][68][69][70][71][72][73]}[60,64,65,66,67,68,69,70,71,72,73,74].

3.1. Economic Market Failure

Imperfect information This barrier refers to the lack of right and proper information about decarbonisation technologies (e.g., abatement potential, fuel saving, cost benefit ratio). Consequently, while such asymmetric information increases uncertainty, it also leads to loss of opportunities to adopt cost-effective technologies owing to such distorted information. The information on decarbonisation measures may be subject to sellers’ opportunism: they may provide right information (or misinformation/biased information) about their technologies; thus, the cost of acquiring the right information becomes higher. Ports, therefore, become wary about the information on technologies even though they fit in properly. If ports have the right information on measures, the risk of not adopting technologies may be reduced. Adverse selection Selection of technologies (measures) by investors (ports) may happen on the basis of visible aspects such as price rather than performance (e.g., abatement potential), owing to the fact that the supplier of technology (vendor) knows more about the technology than the buyer (port). Additionally, the supplier may not relay the information to the other side accurately. Thus, adverse selection is a moral hazard in that actors (ports) may behave opportunistically ^[74][75]. This hinders investment or makes the investor select non-beneficial technology or services. Principle agent relationship (problem) The principal agent contractual relationship is not always efficient. The principal (port authority/landlord) may invest in decarbonisation but cannot see what the agent (port operator/energy provider) is doing. Thus, the principal strictly controls and monitors the agent’s decarbonisation management (i.e., check out the value of investment, requiring short payback rates or high hurdle rates, etc.). This leads to missing opportunities for implementation of better measures in that the agent avoids implementation and even further investment. It is thus important that the agent provides the principal with reliable, accurate, and publicly available information on decarbonisation measures implementation, while the principal needs to streamline and simplify the relationship to improve sustainable performance. Split incentive Split incentive occurs when two parties have different goals (goal conflict) and information (asymmetric information), in addition to the risk bearing costs (cost not shared) such as the case in a landlord-tenant relationship. So, if the costs of investment in decarbonisation measures do not yield benefit to the investor, i.e., measures’ cost is borne by one party while the other enjoys the benefit, this demotivates and decelerates the adoption of the measures. Ports may invest in decarbonisation technologies, but those who run the technology may benefit through energy efficiency or avoiding paying emission tax (regulation compliance) while not bearing the costs or sharing the benefits. This happens between the port authority (landlord) and tenants (private terminal operators, industries), concessionaires, lessees, and other parties under contracts. From another angle, this also includes land transport and ships, as they are the customers of the port. Decarbonization costs ports a fortune, particularly in technologies for decarbonising the ship port interface, such as onshore power supply (OPS), alternative fuel bunkering, pre-booking, just in time (JIT), and virtual arrival ^[75][76][77][76,77,78]. While ship owners, charterers, and even cargo owners gain benefits, i.e., profit by less turnaround time and improving their green image by less carbon foot printing, this leaves ports distanced in implementation. The same is true regarding ports and other subcontractors, for instance the difficulties of energy efficiency management. The landlord, who is legally bound by the government’s regulation to decarbonise, manages his own limited operation and superstructure contrary to subcontractors that have no incentives to manage their operation (energy efficiently) due to their focus on profit, besides the high cost of management (costs of lights and generators renovation and retrofitting including heating and cooling systems, etc.). If ports implement decarbonization measures, the cost is born by ports while subcontractors are free riders (beneficiaries with no costs).

3.2. Economic Non-Market Failure

High costs and access capital issues The costs of decarbonisation technologies are high, including those for port operation (electrification of cargo handling equipment) or ships (OPS). Retrofitting one berth with OPS costs USD 1 million ^[77][78]. The same is true regarding the high cost of investing in LNG and alternative fuel bunkering infrastructure. There is an imbalance between environmental quality and economic feasibility ^[78][79]. Port authorities are aware that an environmental policy generates additional costs and expenses; while they recognise the necessity of it, they attempt to reduce the level of policy intensity or delay its enforcement as much as they can [23]. While the costs are extremely high, lack of capital was also identified as a factor that restricts port sustainability implementation ^[79][80], exacerbated by the lack of subsidies and fiscal regimes that vary too much from country to country. Therefore, restricted access to capital and its high cost (interest rate) is considered to be a key barrier to investment in decarbonisation technologies. The latter is worse in developing countries, where the cost of capital for renewable energy is still very high. Hidden costs The life cycle costs, transactional costs, and commissioning, operation, and maintenance or disruption and other overhead costs (e.g., research, consultancy, feasibility and appraisal studies, procurement, monitoring, data handling, retrofitting, training, commissioning and decommissioning (e.g., large wind generators) may increase the hidden costs and thus hold back deployment of technologies. Risks Investment may be seen as a risk, by risk avert ports, particularly if the payback period is long whilst the technology depreciates fast, and subsidies or grants are unavailable. As such, implementation does not achieve an appropriate return on investment. Another business risk may be seen from the perspective of energy supply (LNG) and security (sanctions) that was compromised during the recent crises in Ukraine/Russia and the Pandemic. On the other hand, the risk of stranded assets and asset specificity are also barriers ^[74][75]. Specificity means that assets are specific for maritime operation and cannot be used outside this domain (port). For example, in relation to the OPS for cruise terminals, not only does seasonality affect this, but also no other ships can use it including other freight transport modes (trains and trucks). On the other hand, stranded assets emerge when a technology becomes non- operational, yielding no benefit, due to its non-usability. For example, LNG bunkering and equipment that is run on LNG will not be used in the future as other zero or near zero emission alternative fuels should be used to reach the climate goal. Heterogeneity Decarbonisation technologies and measures may not be cost effective (efficient) for some ports, including some other polluters (ships, land transport), due to heterogeneity in ports, and its operations and customers. This is to say that ports have different conditions, including governance, business models, geography, throughput, cargo specialisation (container, passenger, RoRo, dry and liquid bulk, and general cargo ships), trade, geographical location, and energy supply and utility. It is worth noting that multi-port stakeholders (government, city, service providers, customers, suppliers, etc.) involved in decarbonisation are also heterogeneous with varying interest and stakes. Satisfying and meeting the expectations of all stakeholders is a complex issue. Generally, what can be applied successfully in one port may not necessarily be successful if implemented in another port. On the other hand, port heterogeneity generates nonuniform responses and complicates the whole implementation process. Furthermore, many ports are considered small vis a vis large ports that have the potential to implement sustainability, such as port differentiated port dues ^[80][81]. Small ports find it difficult to sustain profitability once large costs are incurred in decarbonisation implementation (e.g., the case of ISO certifications ^[81][82]).

3.3. Behavioural Barriers

Form of information The information on decarbonisation’s benefits, abatement potential, return on investment (ROI), and costs is vital to mitigate barriers to implementation. Many ports avoid implementation if they doubt the benefits of technologies. Furthermore, the exchange of requested information among stakeholders, e.g., between ships and ports or port authorities and terminal operators (the case of energy consumption, or carbon foot printing), is not optimal or accurate. This is attributed to confidentiality and reluctancy in data sharing, or just to avoid the high cost of carbon reduction ^[82][83][83,84]. Therefore, the form of information provided should be Specific, Vivid, Simple, and Personal (SVSP). Credibility and trust The lack of credibility and trustworthiness in the technology and service provider (supplier, seller, or vendor) and their information may lead to improper and inefficient choice of decarbonisation measures (technologies). Values Implementation of decarbonisation measures is influenced by norms and values of polluting companies/organisation (ports) [24]. Not having concerns and moral commitment to the environment and society, in addition to lack of real ambition, particularly from top management, influences the adoption of decarbonisation measures. Lack of commitment and disposition of port managers was identified as a barrier to decarbonisation implementation ^[84][85]. Inertia In general, psychological and cultural aspects can also represent challenges for industries’ energy transition ^[85][86]. Resistance, not welcoming change in the work environment, leads to avoiding and ignoring the efforts to decarbonise the port even when cost-effective measures can be implemented. As decarbonisation is an emerging concept, implementation may face strict inertia, particularly by top port management, including other stakeholders, because it is costly and may divert them from conducting profitable business simply and with no complications, i.e., implementation is an extra burden ^[86][87]. Inertia also includes port labour that may favour old Cargo Handling Equipment (CHE) and operations over new equipment that requires new knowledge and training. Another source of inertia may emerge from port surroundings (communities), city boards, NGOs, and other stakeholders who contest (socially acceptance issue) decarbonisation technologies that compromise city safety (e.g., ammonia and hydrogen storage and regasification platforms) and energy intensive technologies (e.g., electrification). Bounded rationality Instead of making rational decisions based on correct information, ports (decision makers) are hooked by bounded rationality; thus, they use the rule of thumb (non-rational decisions) in their selection of decarbonisation measures ^[74][75]. This is attributed to their lack of expertise and the inability to assess the life cycle costs of measures and conduct proper investment appraisals, while also needing to shorten and decrease the time and cost of technology implementation.

3.4. Organizational Barriers

Power When environmental managers in ports lack power and status, the decarbonisation issue has less priority in decision making. This is linked with port institutional power, which is different based on their governance ^[87][88]. Depending on the role of the port authority, implementation of environmental measures differs. In the Hanseatic tradition, e.g., in North Baltic countries, ports are decentralized, and the local government or municipality consequently has strong control over the port. Hence, the port authority has more power and autonomy to implement environmental measures without complications. In contrast, in the Latin tradition, national government has strong control over the port, and thus the port authority has less power and autonomy in taking environmental actions ^[44][88][44,89]. Culture When the culture of the ports (polluters’ organisation) is developed based on respect and appreciation of the environment and effective Corporate Social Responsibility (CSR), decarbonisation issues are always promoted, and thus managers are encouraged to invest in decarbonisation, while individuals (employees) also take actions to decarbonise. This is not the case in many ports though.

3.5. Institutional Barriers

Institutional barriers are issues caused by political institutions, i.e., state government and local authorities ^[67][68]. Major institutional barriers for seaport sustainability are related to supply chain issues that require intersectoral and interjurisdictional collaboration and multimodal integration ^[78][87][79,88]. The institutional structures of firms form their responses to technological opportunities and policies ^[66][67]. The following are various institutional barriers: Political roles Overlapping port governance may undermine the port’s political role in making decisions toward decarbonisation. Overlapping governance is linked to institutional forces ^[87][88]. The unnecessary fragmentation, complexity, and red tape of the multi-level port governance scene definitely decelerates the implementation of environmental measures ^[89][90][90,91]. Zooming out, different political systems between countries and regions may influence the transportation of electricity or fuels, which in turn influence safety and security ^[85][86]. Governmental regulations There is a lack of strict decarbonisation regulations, making ports uncertain about investing in technologies. Absence of regulation, policy, and managerial key performance indicators limits port sustainability performance ^[91][92], which leads to uncertainty in investment ^[85][86]. Even if some regulations are in place, they are not strictly enforced by national and local government or port authorities ^[83][92][84,93]. With no effective regulations, ports may not implement technologies because there is no accountability, and the cost benefit ratio is therefore not above unity. This being so, implementation of strict regulation yields an unlevel playing field that favours ports that do not implement regulation. Overall, existing regulatory and fiscal systems are not helpful; for example, tariff structure do not reward ports for investment in renewable energy. Some regulations may even hinder port investment if they do not allow operation of certain technologies. For example, ports that want to invest in renewable energy (wind or solar) may be hampered by regulations that ban electricity trading (dumping of access energy to the national grid for later reclamation). Similarly, some municipalities may ban the storage of alternative fuels (ammonia, hydrogen) that risk port and city safety. Some cities may even ban the OPS due to the high load on the already weak local grids. This is attributed to lack of codes, standards, local or international regulations, and guidelines for alternative fuels bunkering (e.g., LNG and methanol, hydrogen, and ammonia) or the carriage of alternative fuels by ships. Industrial norms and mimetic actions The norms of ports, for example in training and improving their managers and employee’s awareness and technical skills, are important for better implementation of decarbonisation. Neighbouring ports also play critical roles in port decarbonisation through mimetic and normative forces. Ports that have limited norms pay less attention to environmental issues. Thus, neighbouring ports can mimic such norms leading to similar approaches that do not improve decarbonisation implementation.

3.6. Technological Barriers

Incompatibility There is incompatibility between decarbonisation technologies and port types and operations. Some technologies suit container terminals, whereas bulk or general cargo terminals may have difficulties in implementing the same technology. An example is the OPS barriers (see ^[93][94]) in that bulk ships are rarely fitted with OPS vis a vis liners (passenger or containers) that visit ports very often and may take advantage of ports’ OPS. Additionally, some technologies are not compatible with existing systems, which need separate systems (fuels, and hybrid, electrified, automated and non-automated equipment, etc.). Similarly, there is an issue concerning port OPS and charging stations when their voltage and frequency is not compatible with ships ^[94][95]. Many ports lack physical spaces for new technologies. For example, bunkering storage with safety zones, OPS, charging stations, and new maintenance stations, require new and large expansions that many ports do not have space for. Interference with ports’ main processes Some technologies may interfere with port operations and create issues. For instance, a fault in a smart grid may lead to corruption of perishables or logistics inefficiency, making the port accountable. Additionally, port decarbonisation may depend highly on electrification. Thus, peak load may demand more electricity than is available or based on renewables. On the other hand, digitalisation (information communication technology) triggers cyber security issues, which may leak port information, compromising privacy and competitiveness. The complexity of measures There are various complexities in technology implementation, which result in reluctance in its initiation. Some technologies require new infrastructure or long renovation or construction times, such as large fuel storage facilities, OPS infrastructure, and large batteries that take space and thus may hinder some operation. OPS is generally influenced by the source of port electricity (green or otherwise), type and frequency of calling ships, and distance to the city grids. The time taken to connect and disconnect the OPS, or charging, is another issue, particularly for ships with limited berth windows (RoRo, container, passenger and ferries); connection and disconnection of OPS may take up to one hour, which may increase a ship’s turnaround time ^[77][78]. The same is true regarding limited national grid capacity that cannot feed the port OPS. Technology readiness and abatement potential While some decarbonisation technologies are available, some may not give high outputs (e.g., renewable energy generation through tide or wave energy) or abatement potential (e.g., pre and after treatment technologies for cargo handling equipment). Ports that are not sure about the abatement (not being at least verified) would not invest in the technology. On the other hand, although some alternative fuels, including biofuels, are being used in the market, the availability in large scale is still limited ^[95][96]. Ports may need to compete with other industries and sectors to get access to such fuels. Furthermore, some technologies, such as carbon capture and storage or utilisation, are not yet mature. The latter does not even have a potential market thus far.

3.7. Time Barriers

Generally, decision making takes time and deploying measures also takes time. Also, some technology implementation decisions may need to go up to local, national, and federal governments and diverse ministries and organisations at different hierarchy levels ^[86][87]. This behaviour leads to long lead times for taking decisions (or to outdated decisions being made). On the other hand, some ports may already have long-term agendas and strategic plans that do not count decarbonisation as a priority.

3.8. Administrative Barriers

The administrative barrier occurs when a port lacks the awareness, guidelines, resources, experienced staff, and technical skills to analyse, make decisions, and oversee the implementation of decarbonisation solutions ^{[83][96][97][98]}[84,97,98,99]. Additionally, there is a large number of diverse small ports (companies) that may not have the management expertise needed to evaluate and implement decarbonisation solutions. This is further complicated when ports use third-party services to conduct some business (such as operators, 3PL, etc.). In this case, ports as landlords may be removed from day-to-day operational issues leading to lack of ability to administrate decarbonisation. On the other hand, there exist administrative conflicts inside the port different department. For example, a finance department may favour low capital cost, procurement may favour heavy duty and operationally efficient technologies, while environment and energy departments may focus on lower abatement potential and greater energy efficient technologies.