Energy Consumption and Carbon Footprint of the Port of Sines: Contribution to Maritime Transport Sustainability

Abstract

Calculating the energy consumption and carbon footprint is essential for maritime industry sustainability, driving informed decisions and innovation. This study assesses the energy consumption and carbon footprint of the Port of Sines in Portugal to support its decarbonization and energy transition, based on the scopes defined by the Greenhouse Gas Protocol. The proposed calculation model is detailed using different data sources for the 2018–2022 period. For each terminal, the monthly and annual energy consumption and carbon footprint are calculated, considering land and maritime activities into the port jurisdiction area. The results show that more than 99% of the port’s total energy consumption and carbon footprint are due to the operations and activities of the different terminals. On average, the Port of Sines consumes 422,378.45 MWh/year and has a carbon footprint of 224.63185 tCO₂eq/year. The analysis reveals a non-linear relationship between energy and carbon footprint, due to the different port activities, emphasizing the need for tailored decarbonization strategies for each terminal.

1. Introduction

In light of the global nature of maritime transportation, several countries and regions bear responsibility for initiatives aimed at reducing risks, enhancing safety, and preventing pollution [1,2,3]. This diversity of interests fosters the coordination of efforts on a global scale, leading to the adoption of standards and practices for the entire sector. These standards and practices encompass not only activities on the high seas but also those conducted within the maritime ports [1,2,3].

The year 1950 marked a turning point with the transportation of a substantial volume of hydrocarbons by sea, prompting heightened awareness of the potential dangers to marine ecosystems from oil spills. In response to this growing concern, the first International Convention for the Prevention of Pollution of the Sea by Oil (OILPOL) was established in 1954. Subsequent to this, in 1973, the International Convention for the Prevention of Pollution from Ships (MARPOL) was endorsed, thereby expanding the scope of the original convention and replacing it [1]. Nevertheless, OILPOL remains the foundational document for those nations that have not adhered to MARPOL [2]. MARPOL [1] and its protocols comprise the international treaty that aims to further mitigate marine pollution [3,4].

The establishment of the Marine Environment Protection Committee (MEPC) in 1973 marked a significant development in this regard [5]. The MEPC, functioning as the senior technical body within the aim of the International Maritime Organization (IMO), plays a pivotal role in addressing the challenges posed by ship-based pollution. This encompasses the mitigation of emissions that pose a threat to human health and contribute to environmental degradation and climate change.

A primary objective of MARPOL is to safeguard the well-being of both humans and the marine environment [1,6]. The MEPC is structured into six annexes, among which is Annex VI, Prevention of Air Pollution in Ships (1997), which entered into force in 2005 and deals with emissions. This annex establishes the policies regarding the regulation of emissions and includes mandatory procedures to prevent atmospheric pollution. Chapters 3 and 4 include the policy established to achieve the reduction in emissions in maritime transport activity [1,6]:

• Regulation 12: The Montreal Protocol on Substances that Deplete the Ozone Layer [7] and its amendments.
• Regulation 13: Nitrogen oxides (NOx).
• Regulation 14: Sulphur oxides (SOx) and particulate matter (PM).
• Regulation 15: Volatile Organic Compounds (VOC).
• Regulation 18: Fuel oil availability and quality.
• Regulation 22: Energy Efficiency Design Index (EEDI).
• Regulation 23: Energy Efficiency Existing Ship Index (EEXI).
• Regulation 24: Required EEDI.
• Regulation 25: Required EEXI.
• Regulation 26: Ship Energy Efficiency Management Plan (SEEMP).
• Regulation 27: Collection and Reporting of Ship Fuel Oil Consumption Data.
• Regulation 28: Carbon Intensity Indicator (CII).

In 2018, the MECP.304 (72) [8] established the Initial IMO Strategy on Reduction of GHG Emissions from Ships including targets for emission reduction in the entire maritime industry in the Roadmap. This strategy includes steps for the carbon intensity of the ship, carbon intensity of international shipping, and greenhouse gas (GHG) emissions from international shipping to peak and decline by 2030 and 2050.

In 2023, the MECP.377 (80) [9] revised the Initial IMO Strategy [8] and established the IMO Strategy on Reduction of GHG Emissions from Ships, which includes indicative checkpoints to reach net-zero GHG emissions from international shipping:

• To reduce the total annual GHG emissions from international shipping by at least 20%, striving for 30%, by 2030, compared to 2008.
• To reduce the total annual GHG emissions from international shipping by at least 70%, striving for 80%, by 2040, compared to 2008.

The MECP.377 (80) [9] includes the following measures: “consider and analyze measures to encourage port developments and activities globally to facilitate reduction of GHG emissions from shipping, including provision of ship and shoreside/onshore power supply from renewable sources, infrastructure to support supply of zero or near-zero GHG emission fuels and/or energy sources, and to further optimize the logistics chain and its planning, including ports”.

Maritime ports play a crucial role in the loading and unloading of cargo, as well as in the provision of logistical services. However, this activity faces the challenge of reducing the emissions originating from ships, port authorities [10], and port operations [4,11,12]. The development of a decarbonization plan for port activity, based on the quantification of emissions, is identified as a pivotal task for managers, users [11], and researchers in this domain [4,11,12,13,14,15].

The calculation of the energy consumption and carbon footprint contributes to the sustainability of maritime transport by providing a basis for informed decision-making. Quantifying these metrics enables the identification of opportunities for enhancement, such as the implementation of strategies to improve energy efficiency [16] and reduce fossil fuel consumption [17] and emissions [12]. The continuous monitoring of these metrics enables the assessment of progress toward established emissions reduction targets and the demonstration of commitment to complying with regulatory obligations [9,18,19]. This comprehensive approach is instrumental in catalyzing innovation, fostering collaboration within the supply chain, and promoting the development of more sustainable and resilient maritime transportation systems [9,18,19].

As the accuracy of the calculation of the carbon footprint increases, the methodological complexity and information requirements also rise. The involvement of external agents to the organization itself considerably expands the complexity of the calculation, due to the amount of information required and the difficulty of making it available [20]. However, the greater detail and the comprehensive nature of the calculation make it a suitable tool for the establishment of emission reduction policies and thus for achieving carbon neutrality [21,22,23].

Maritime transport contributes as a fundamental pillar of the Portuguese economy, which increases its responsibility for the sustainable use of marine and coastal resources, while it stimulates economic development. In 2018, the broad spectrum of maritime activities contributed 5.1% to the gross domestic product (GDP) and 4% to national employment. Notably, the port sector accounted for 5% of the country’s total exports in the same year [24], surpassing the European Union (EU) average in terms of cargo volume. This transition presents a significant opportunity to enhance Portugal’s standing on the global stage. In this context, it is imperative to address the global challenges related to climate change, decarbonization of the maritime industry, and the enhancement of long-term sustainability in this sector [11,13,25,26].

Due to its localization and characteristics, the Port of Sines has a strategic importance in Europe, and it is considered its Atlantic Gate [25]. The present study aims to provide a comprehensive energy consumption characterization and carbon footprint analysis of the Port of Sines during the period of 2018 to 2022 as a contribution to maritime transport sustainability.

This study involves the definition of a calculation model integrating multiple data sources from the Port Authority and also from its concessionaires and terminals. This methodology addresses the knowledge gap concerning the decarbonization of multi-terminal and multimodal maritime ports. The implementation of this methodology contributes to the development of best practices in the maritime transport supply chain.

For maritime ports, although there are several methodologies for assessing carbon footprint, different contexts and challenges in accessing data often impose restrictions in the calculation of the indirect emissions of ports [27]. The developed methodology was based on the recommendations of the GHG Protocol [28], on the Port Emissions Toolkit [29], and other relevant publications [18,20,30,31,32,33,34,35]. It aims to reflect the multi-operational specificities, within the multi-terminal and multimodal logistics node of the Port of Sines. Such specificities include a variety of cargo types, transport modes, and distinct terminal characteristics [18,20,30,31,32,33,34,35].

Several studies only contemplate specific terminals or transport modes [20,21,27,35,36]. Nevertheless, few studies [32] consider a methodology that assesses the total port emissions, such as the present case study, where we analyze both energy consumption and carbon footprint for land and maritime transportation. Among the main data sources were the Port Single Window (JUP) and the Logistics Single Window (JUL) [37], which provided data on ship characteristics, movements, and land transport. The specific emission factors were obtained from Portuguese Environment Agency (APA) reports [38]. The methodology employed is replicable on other ports [13,20,21,27,35,36].

The following sections provide a comprehensive description of the materials and methods used in the study and the main results obtained by terminal, considering the diversity of cargo types and emission factors, and finally, the most important conclusions of the study.

2. Materials and Methods

2.1. Port of Sines, Portugal

The Port of Sines (Figure 1) is a piece of maritime infrastructure of vital importance to Portugal, the EU and other countries outside this region. Its location on the Atlantic coast, depth, and facilities make it at an important logistics node. One of the port’s main natural characteristics is its natural depth, with an average of 18 m (max. of 28 m), which is greater than many other maritime regions [21,39].

At present, the Port of Sines has the most important container terminal in the country and is among the most significant ports within the EU, playing a significant role in facilitating international trade and cargo transportation. Additionally, the port’s strategic position in the energy sector, acting as a pivotal hub for the reception of liquid fuels, contributes to the economy and serves as a significant asset for the integration of Portugal within the European market [40].

In 2024, the Port of Sines managed a total cargo of 47,827,062 t, marking an 11.3% increase compared to the same period in the previous year. Concurrently, the number of ships operating within the port decreased by 1.4%, with a total of 1839 ships managed.

Table 1. Cargo handling and country of origin/destination in the Port of Sines in 2024 [41].

Cargo Handling	Total (t)	Total (%)
Liquid bulk	24,253,862	50.71
Dry bulk	401,206	0.84
General cargo	23,171,994	48.45
Country of Origin/Destination	Total (t)	Total (%)
Continent and autonomic region	3,379,627	7.06
EU countries	9,061,815	18.94
Other countries	35,385,619	74.00
Total Cargo	47,827,062	100.00

provides a detailed distribution of the cargo by terminal and the respective origin and destination [41].

2.2. General Description

In order to achieve the goal of carbon neutrality, the IMO has established 2008 as the baseline year for comparison, with targets defined for the years 2030 and 2040 [9]. However, an alternative baseline year may be selected, depending on data availability [29]. Tank to wheel (TTW) emissions are taken into consideration [23], classified according to the three scopes of the GHG Protocol [28], which is recommended for analogous studies [29]. For each scope, emissions from land-based and maritime activities, as well as stationary and mobile activities, have been estimated for the Port of Sines jurisdiction area (AJAPS), along with each terminal and the different types of services.

The Port of Sines features five specialized terminals with private concessions, including the Containerized Cargo Terminal (SCT), Liquid Bulks Terminal (LBT), Liquefied Natural Gas Terminal (NGT), Petrochemicals Terminal (PCT), and Multipurpose/General Cargo Terminal (GCT). This last terminal replaced, in 2022, the previous Dry Bulk Terminal (DBT). Additionally, the “Others” category encompasses the Sports and Fishing Port, the tugboat service concession, and electrical services provided to the Sines Industrial and Logistics Zone (ZALSINES). These entities possess a variety of maritime and inland infrastructures, technologies, and inland transport modes for their cargo, among other attributes. The aforementioned factors result in a calculation of energy consumption and carbon footprint that is differentiated for each terminal [42].

Table 2. Depth and cargo type from the different terminals of the Port of Sines [41].

Terminal	Depth (m)	Cargo Type
SCT	17	Container
LBT	28	Crude oil, refined oil, liquefied petroleum gas, methanol, and chemical naphtha
NGT	15	Liquefied natural gas (LNG)
PCT	12	Propylene, ethylene, butadiene, ethyl tertiary butyl ether, ethanol, methyl tertiary butyl ether, aromatic mixtures, and methanol
GCT	18	Dry bulk, general cargo, and roll-on/roll-off (ro_ro)

and Figure 2 provide a description of the terminals and, in general terms, the aspects considered in each scope in the methodology.

The methodology considers the consumption of fuels and electricity used and their respective emission factors. Furthermore, the statistics of ships and cargo managed by each terminal for the period 2018–2022 was obtained from Ports of Sines Authority (APS) statistics reports, JUP/JUL platforms, and concessionaires. In MECP.377 (80) [9], the base year for comparison is 2008. However, there are only complete data available to calculate the three scopes from 2018. In this sense, this has been considered as the base year.

2.3. Scopes

Scope 1 [28] considers the consumption of fossil fuels used by the Ports of APS for land and maritime activities carried out within the jurisdiction area. Scope 2 [28] encompasses the electricity consumption calculated based on the purchase and sales by APS. Scope 3 [28] involves the calculation of energy consumption for the maritime and land transport activities at each terminal, in addition to its electricity consumption. While the calculation of Scope 3 encompasses indirect emissions, it is crucial for the establishment of effective emission reduction policies at the port. This is due to the fact that it enables the identification of the main emission sources associated with the concessionaires and the implementation of joint measures [14].

For Scope 1 [28], the following fuels are considered:

• Natural gas for boilers.
• Diesel fuel for the emergency power plant.
• Diesel fuel for employees’ collective transport vehicles.
• Diesel and gasoline fuel for private employee transport vehicles.
• Diesel fuel for the pilot boats within the AJAPS.

Scope 2 [28] includes electricity consumption based on the records kept by APS and the emission factors of APA [38].

Scope 3 [28] includes the calculation of energy and emissions from the activity carried out by the concessionaires in the different terminals. Energy consumption and carbon footprint are calculated for the end use of electricity and for maritime and land transport [29].

2.4. Scope 3

Table 3. Ship type and terminal data in the Port of Sines (2018 to 2022).

Terminal	Ship Type	Land Equipment	Ship	Cargo (t)	ME (Hp)	DWT (GT)	Dwell Time (h)
			AVG	AVG	RAN	RAN	AVG
LBT	Maritime liquid bulk carrier	Centrifugal pumps for the discharge of liquid bulk	767	18,097,056	1362–29,677	495–161,579	44.98
NGT	Maritime liquified natural gas carrier	Cryogenic centrifugal pumps for liquefied natural gas discharge Cryogenic heavy-duty trucks	135	3,860,389	23,119–63,594	90,835–128,806	71.48
SCT	Maritime container carrier	Electric rubber-tired gantries (RTG) and Rail-mounted gantries (RMG) Electric train loading container terminal Heavy-duty truck container terminal	887	20,153,792	2434–82,059	256–232,618	42.35
PCT	Maritime petrochemical carrier	Centrifugal pumps for the discharge from the petrochemical industry Heavy-duty trucks of the petrochemical industry	61	499,099	1978–6572	2815–13,794	75.23
GCT	General cargo ship	RTG and RMG by diesel fuel Heavy-duty trucks	128	2,029,792	1369–69,619	1864–90,449	54.62
Total			1850	42,610,336	1362–82,059	256–232,618	57.73

ME: main engine; DWT: deadweight tonnage; AVG: average; RAN: range.

presents the annual average of the data from each terminal for the study period, used for Scope 3, where even though “Others” are considered in the calculation of this scope, their data are not featured in the following table, due to their high variability. As can be seen in the table, there is a diverse range of types of ships (with different main engine and deadweight tonnage), maneuvering times and equipment for load/unload cargo for each terminal. Additionally, Scope 3 includes the energy consumption and the calculation of the carbon footprint of the sport and fishing ports, ZALSINES, and the ship service tugboats, since these are operated by concessionaires.

2.4.1. Maritime Transport

Regarding the ship movement data, until 2019, the maritime transport information was obtained from the JUP. In 2020, the JUL information system replaced the previous JUP, according to Law Decree No. 158/2019 [37]. The JUL is the technological platform for defining and supporting the flow of information relating to the formalities of declaration, planning, execution, and monitoring of the maritime transport logistics chain that ports use in Portugal. This platform contains a wide range of information, including details on ship characteristics, cargo declaration, access to facilities, operations in the terminals, and other maritime logistics data. It also provides transport information on road and railway movements [43].

Furthermore, the information regarding maritime transport includes [37,43]:

• The type of ship and fuel used, IMO id, and other pertinent features.
• The type and times of maneuvers per terminal: The Passenger Locator Form (PLF)-Entry, anchoring, suspending, berthing, departing, and PLF-Exit maneuvers.

The calculation of the emissions is carried out based on the information regarding the type of ship, the fuel used, and the time duration of the maneuvers, according to the methodology recommended in the European Environment Agency (EEA) [33]. This methodology involves the calculation of the energy consumption and emissions as a function of the power and load factors of the ME and auxiliary engine (AE) of the ship, as well as the execution time of each maneuver within the AJAPS. The load factor, AE/ME proportion, and fuel type are also considered. In this methodology, the AE is estimated as a percentage of the ME depending on the type of ship, regarding the EEA [33].

A total of 28,785 maneuvers were analyzed during the 5-year period of the study; however, only 48% of these data included the power of the ME. To complete the data for the missing values [44], they were assigned based on linear regression.

2.4.2. Land Transport

For land transport, the following fuels are considered:

•

Diesel and gasoline for the pendular movement of employees by terminal in private and collective vehicles. It is noteworthy that these data are not typically included in the carbon footprint calculation models [15]. In the present study, all data from these calculations were considered to ensure enhanced accuracy and detail in the model. The following data were considered:

o

Number of employees at concessionaires and terminals, provided by APS.

o

Vehicle occupancy rate: 1.2 passengers/vehicle.

o

Distribution of vehicles: 60% diesel and 40% gasoline.

•

In accordance with the methodology, only the journey within the AJAPS was considered.

•

Diesel for the transport of cargo by container, general cargo, and cryogenic trucks for LNG terminal.

•

Electric power for the train line for container transport. Full locomotive and full truck (cargo) are the load factors considered.

2.4.3. Electrical Energy Consumption

The electric energy consumption data were derived from APS records concerning the energy purchases and sales, which were provided to the terminal operators. Additionally, the energy data supplied by external electricity providers to the NGT and PCT were used. Similar to Scope 2, the emission factors are the ones defined by APA for each year [38].

3. Results and Discussion

As described in Section 2, the proposed methodology can be replicated at other multi-terminal and multimodal maritime ports by considering factors such as maritime and land boundaries, classification of emission sources by Scope, data sources of operations and emission factors, type of ships and cargo for each terminal, land operation modes, historical records of maritime and land operations, and type of equipment for loading and unloading, among others.

The calculations of energy consumption and carbon footprint were made on a per-movement basis for each type of cargo and then analyzed on a monthly and annual basis.

Table 4. Energy characterization and carbon footprint of the Port of Sines. Annual average value for the period 2018–2022.

Energy Consumption (MWh)
Scope	2018	2019	2020	2021	2022	Average	Average (%)
1	1758.78	2024.81	1802.64	1799.73	1601.66	1797.52	0.43
2	1600.12	1613.60	1367.00	1643.00	1504.00	1545.54	0.37
3	386,686.69	380,522.45	413,976.29	536,283.83	377,707.63	419,035.38	99.21
Total	390,045.59	384,160.87	417,145.93	539,726.56	380,813.29	422,378.45	100.00
Base (%)	100.00	98.49	106.95	138.38	97.63
Carbon Footprint (tCO2eq)
Scope	2018	2019	2020	2021	2022	Average	Average (%)
1	593.94	742.29	593.73	579.18	545.99	611.03	0.27
2	459.00	376.00	251.00	266.00	205.00	311.40	0.14
3	226,347.11	179,767.30	217,452.23	300,064.52	194,915.94	223,709.42	99.59
Total	227,400.05	180,885.60	218,296.96	300,909.70	195,666.93	224,631.85	100.00
Base (%)	100.00	79.55	96.00	132.33	86.05

and

Table 5. Energy characterization and carbon footprint of Scope 3 of the Port of Sines. Average value for the period 2018–2022.

Energy Consumption (MWh)
Font	SCT	LBT	NGT	PCT	GCT	Others	Scope 3	Scope 3 (%)
Electric energy	17,163.28	4776.63	62,053.12	31,634.13	2209.22	733.45	118,569.83	28.03
Land transport	3032.28	214.00	228.95	86.60	455.07		4016.90	0.95
Maritime transport	59,356.17	192,397.26	19,142.65	4425.97	21,126.60	3978.61	300,427.26	71.02
Total	79,551.73	197,387.89	81,424.72	36,146.70	23,790.89	4712.06	423,013.99	100.00
Contribution (%)	18.81	46.66	19.25	8.55	5.62	1.11
Carbon Footprint (tCO2eq)
Font	SCT	LBT	NGT	PCT	GCT	Others	Scope 3	Scope 3 (%)
Electric energy	3405.46	968.07	12,269.49	6218.96	523.05	150.00	23,535.03	10.33
Land transport	408.09	28.76	30.81	11.66	61.24	--	540.60	0.24
Maritime transport	41,494.34	135,238.27	5087.54	3109.00	14,886.23	3978.61	74,524.11	89.43
Total	45,307.89	136,235.10	17,387.84	9339.62	15,470.52	4128.61	227,869.58	100.00
Contribution (%)	19.88	59.79	7.63	4.10	6.79	1.81

show energy characterization and carbon footprint averages. It can be observed that, on average, over 99% of the energy consumption and carbon footprint is attributable to Scope 3.

Considering the year 2018 as a baseline, Figure 3 presents a non-linear relation between the independent variables (number of ships and total annual cargo) and the dependent variables (total energy consumed and carbon footprint).

Specifically, regarding 2018, it can be noted that in the year 2022 there is a reduction of 20% in the ships served and 6% in the managed cargo:

• During the period between 2018 and 2021, the energy consumption increased by 38% and the emissions by 32%, despite the reduction in the number of ships and cargo handled.
• The year 2021 has the largest energy and carbon footprint values. This can be explained by the increase in anchoring and berthing times in most of the terminals (Figure 4) [45].
• In 2022, we observed a decrease in both energy consumption (2%) and carbon footprint (14%).
• Table 6. Ship, cargo, energy consumption, and carbon footprint correlation for the Port of Sines. Average value for the period 2018–2022.

  Dependent Variable	Independent Variable	Correlation (R2)
  Energy	Ship	0.3032
  	Cargo	0.1007
  Carbon Footprint	Ship	0.2030
  	Cargo	0.3432

  shows the correlation between energy consumption, carbon footprint, number of ships, and cargo handled. In this table, it can be observed that there is no significant correlation between these variables.

A closer examination of Figure 4 and Table 5 reveals distinct patterns. The LBT exhibits the highest values for both energy consumption and carbon footprint, while ‘Others’ show the lowest values. However, in the top two for energy consumption is the NGT, which does not match this position in terms of carbon footprint, as it has been displaced by the SCT. This indicates heterogeneity in the relation between the variables. For LBT, Others, SCT, and GCT, the highest consumption is attributed to maritime transportation. In contrast, the emissions produced by tugboats are less significant. PCT and NGT demonstrate the highest levels of electric energy consumption, while SCT and GCT exhibit a consumption rate between 4% and 2%, respectively, related to land transport freight.

Figure 5 presents this consumption in absolute values, and it is evident that the LBT has the highest value due to maritime transport, matching with being the deepest terminal. Figure 6 and Figure 7 show the Sankey diagrams for the energy consumption and carbon footprint for the year 2022. Figures illustrates the highest energy consumption of each terminal, where it is evident that it depends on their characteristics.

In Table 3 and Table 4, for the period 2018 to 2022, the total carbon footprint was reduced by 13.95%. This is due to several factors:

(a)

Scope 1, which is the emissions due to the consumption of APS fuels. During this period:

a.

The boiler’s natural gas consumption was reduced due to the closure of a restaurant in 2021.

b.

During the years 2021 and 2022, fuel consumption for electrical plants was not reported.

c.

There is a 15.7% reduction in diesel consumption of the pilot boats.

(b)

Scope 2, which concerns the emissions related to the electric energy consumption in the APS, was significantly reduced, due to the 44.5% decrease in the emission factor reported by APA [38] for this period. This was due to the incremental use of renewable energy in Portugal [46].

(c)

Scope 3 represents the carbon footprint of the concessionaries. During this period:

a.

On average, LBT contributed to 59.79% of the carbon footprint. In addition, 99.3% of its emissions are due to maritime transport. For this period, the managed cargo increased by 17.2% and the number of ships served by only 2.3%, going from 23,238.2 to 26,467.6 t/ship, that is, larger ships were attended. On average, 56% and 36% of the emissions occur during anchoring and berthing, respectively. During 2022, there was an increase in these times of 31.3% and 15.9%, respectively. Even the percentage of ships anchoring increased from 51% to 61% during this period, which indicates that the measures to reduce its carbon footprint must be aimed at lowering the percentage and anchoring time of the ships.

LBT terminal has the greatest depth (Table 2) and is in second place in terms of ships served (Table 3), with a large variety of ship types. In addition, based on the model for calculating emissions from maritime transport, the load factor of the AE is higher in these types of ships [33]. Figure 8 shows, on average, the percentage of emissions by type of maneuver for this terminal.

b.

The SCT contributes an average of 19.88% to the carbon footprint. This terminal, in December 2019, increased the number of cranes to 10, which improved the efficiency in the loading and unloading of the container ships. In total, 91.2% of their emissions are due to maritime transport, related to 27% and 52% that occur during anchoring and berthing, respectively. For this period, the percentage of ships anchoring decreased from 9.9% to 4.8%. However, there was an increase in the berthing time of 29.9%, due to an increment in the cargo handled from 1726.3 to 2104.6 TEU/ship. This represents the most efficient terminal in the port due to its relatively low number of ships in anchoring phase. The remaining emissions are due to electric energy consumption (7.5%) and land transport. The electric energy in this terminal is used for the operation of cranes and gantries and their building headquarters, which had an increase in consumption. However, thanks to the decrease in the emission factor [38], the carbon footprint has been reduced.

Finally, the land transport contributes to 1.3% of the carbon footprint, where 70% of this value is related to the transport of cargo within AJAPS (30% and 40% by rail and road transport, respectively) in 1.9 km (rail) and 2.1 km (road).

For this type of terminal, measures to reduce its carbon footprint are found to be related to the use of alternative fuels in AE, increasing the efficiency of its engines, or the possibility of their replacement by electrical engines fed from the terminal during the berthing process, which represents 41.9% of the total operation time in the port and a 51.8% contribution to the emissions. This terminal has the greatest number of ships served (Table 3) and DWT. Figure 9 shows the average percentage of emissions by type of maneuver of this terminal.

c.

NGT contributes to 7.63% of the carbon footprint. Unlike the other two terminals, 70.6% is due to energy consumption of the facility pumping systems for loading and unloading ships. This terminal has an increase in its cargo and number of ships for this period, which has a positive impact on the energetic transition of the country, with LNG being the fuel that has replaced coal in its electrical power plants [26]. However, this has gone from 63,396.6 t/ship to 59,271.9 t/ship for the years 2018 and 2022, respectively. A total of 29.2% of its carbon footprint is due to maritime transportation, which has been reduced thanks to the decrease in the anchoring and berthing times of 16.9% and 5.06%, respectively. In addition, there has been a reduction from 13% to 9% in the ships that anchor. Less than 7% of its cargo is transported by land, hence the contribution to the carbon footprint is less than 0.2%. As a measure to decrease the carbon footprint, the reduction in the emission factor by electricity consumption must be included [38], aligned with the decarbonization policy of the energetic matrix in Portugal [26].

Additionally, during the unloading process of the cryogenic ships, there are cold losses that could be recovered to reduce the refrigerant consumption in the SCT reefer containers and, as a consequence, the port’s total carbon footprint, promoting the circular economy. Figure 10 shows the average percentage of emissions by type of maneuver at this terminal.

d.

GCT, PCT, and Others contribute a total of 12.7% to the port’s carbon footprint. Approximately 80.6% of this footprint is due to maritime transportation. Of this value, 35.6% is emissions due to the use of the tugboats, which decarbonization would impact positively in reducing the total carbon footprint. By the second half of 2022, the GCT replaced the DBT, which has had a positive impact by reducing its carbon footprint.

e.

The carbon footprint of the PCT is due by 67% and 33% to electrical energy consumption and maritime transportation, respectively. The carbon footprint from the consumption of electric energy has been decrease thanks to the reduction in the emission factors [38]. An average of 3593.7 t/ship of maritime transport is maintained despite the increase in its managed cargo by 18%, guaranteeing its efficiency. Meanwhile, 65% of its emissions are due to anchoring and only 30% due to berthing. However, the times of these operations have been reduced by 75.3% and 7.2%, respectively. In addition, the percentage of ships in anchoring has reduced from 68.8% to 37.5%, demonstrating improvements in efficiency from a logistical point of view.

On average, the anchoring time and emissions from this terminal account for approximately 46.5%, a similar value to berthing. To reduce the carbon footprint, increasing efficiency in the logistics of ship waiting times and implementing measures for the AE can be effective.

The carbon footprint of the Port of Sines’ terminals is contingent on maritime activity, particularly berthing and anchoring maneuvers (Figure 8, Figure 9 and Figure 10). Given the risks associated with BLT, GNT, and PCT [47,48,49], some of the potential mitigation strategies are included in

Table 7. Potential mitigation strategies to reduce energy consumption and carbon footprint correlation at a maritime terminal port.

Measures	Alternatives	LBT	GNT	SCT	PCT	GCT	Other
Maritime transport decarbonization	Adoption of alternative fuels for ships: LNG, hydrogen, biodiesel, methanol, and ammonia [13,34,49]	•	•	•	•	•
	Implementation of SEEMP, EEDI, and EEXI [1,6]	•	•	•	•	•
	Implementation of offshore power supply with renewable energy [9,36]			•		•
	Implementation of onshore power supply with renewable energy [9,34]			•		•
	Pilot boats and tugboats: Transition from fossil fuels to electrical energy [50,51]	•	•	•	•	•	•
	Reduction in anchoring and berthing time [13]	•	•	•	•	•
Land transport decarbonization	Cranes and other land equipment: Transition to electric power [52,53]			•		•
	Electrification and hybridization with renewable energy [13,34]	•	•	•	•	•	•
	Increase cargo transportation by train [54]			•		•
Electrical energy consumption decarbonization	Increase the implementation of smart grids and microgrids with renewable energy [55]	•	•	•	•	•	•
Carbon offsetting	Nature-based solutions for carbon capture, such as afforestation and ecological restoration [56,57]	•	•	•	•	•	•
	Cold loss recovery and supply for replacing refrigerant consumption in other terminals [20]		•
	Wastewater and solid waste treatment [58,59]	•	•	•	•	•	•

Note: The dot (•) symbol indicates a correlation between the corresponding row and column.

. These measures are supported by several policies and regulations that are already ongoing in the maritime sector at global and European levels [47,48,49].

4. Conclusions

The following work includes the energy characterization and carbon footprint calculation of the Port of Sines for the period of 2018–2022. This characterization is carried out for each of its terminals and their specific activities. Within this framework, it is shown that Scope 3, due to the activity of the concessionaires and the movement of cargo, contributes more than 99% of the energy consumption and carbon footprint of the port as a whole. The study also revealed that with the reduction in the attended ships, there was a decrease in diesel consumption of the pilot boats, which impacted the total carbon footprint of Scopes 1 and 3.

The Port of Sines’ importance for the country’s energy sector is accomplished through its dedicated liquid fuels and liquefied natural gas terminals, which reveal the importance of its carbon footprint assessment and reduction. On average, these terminals represent 65.9% of the energy consumption and 67.4% of the carbon footprint of the port. This is due to the timing of the different maritime operations, particularly berthing and anchoring maneuvers.

The maritime container terminal is the one that manages the largest cargo of the Port of Sines. However, on average, it only represents 18.8% of the energy consumption and 19.9% of the carbon footprint. The total dwell time of this terminal’s ships within the area of jurisdiction is the shortest of all the terminals. In addition, the cargo unloading equipment is electric, eliminating emissions from diesel fuel consumption. For decarbonization, alternatives such as onshore and offshore power supply can be implemented. Even with a connection to the public grid, the emission factor of Portugal’s energy matrix is being progressively reduced.

On average, the Port of Sines consumes a value of 422,378.45 MWh/year and has a carbon footprint of 224,631.85 tCO₂eq/year. Being a multi-terminal and multimodal port, its calculation model was non-homogeneous and has required detailed data to ensure its accuracy. We observe that the variables that impact in the characterization of consumption energy and carbon footprint depend on the characteristics of the ships and the modes of transit of cargo.

MECP.377 (80) [9] requests a reduction in GHG emissions from international shipping by at least 20% by 2030, compared to 2008. Although the present work considers the base year of evaluation of 2018, the Port of Sines had reduced its carbon footprint by 13.95% by 2022. This is mainly due to the increase in the cargo per ship, the transition in the Portuguese energetic matrix, and also the improvement of the efficiency in the maritime operation, mostly in the container’s terminal.

The model proposed in this paper considers the diversity of information sources, maritime operations, cargo types, and ships, among other relevant aspects. This adaptability makes it a particularly useful tool for multi-terminal and multimodal ports, where heterogeneity of activities and infrastructures is a predominant characteristic.

The results obtained allow for the identification of the main sources of greenhouse gas emissions and have allowed the identification of the most promising improvement opportunities. The findings of this study have significant implications for strategic decision-making in the Port of Sines and can be used as a model for achieving carbon neutrality in Sines and in the maritime transportation sector.