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.
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 and
Table 5 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 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. 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.