Analysis of the Carbon Intensity of Container Shipping on Trunk Routes: Referring to the Decarbonization Trajectory of the Poseidon Principle

Abstract

Container shipping industries are highly capital intensive. If shipping carriers want to execute international shipping financing, they must follow the IMO emission reduction targets and meet the decarbonization trajectory of the Poseidon Principle (PP). This article used an activity-based model to calculate container shipping industry carbon emissions. It was found that the carbon intensity per unit for each ship was decreased because of the upsizing of container vessels and route deployment based on the alliance strategy. On the Asia–Europe (A/E) trunk route, as the ship size increased from 11,300 to 24,000 TEU, the results showed that the carbon intensity ranged from 6.48 to 3.06 g/ton-nm. It is also proven that the mega-container deployment on the A/E trunk route followed the decarbonization trajectory proposed by PP, while the Asia–Pacific trunk route was not fully in line with the trajectory of EEOI/AER. It is worth noting that starting from 2020, due to the COVID-19 pandemic, shipping companies deployed a higher number of small-size vessels to boost revenues, resulting in more pollutants produced and a mismatch of the trajectory proposed by PP.

1. Introduction

The International Maritime Organization (IMO) is a specialized agency of the United Nations that has been promoting green shipping for years; however, the targets of green shipping were not fully fulfilled because most of the container carriers focused on financial performance rather than the achievement of emission reduction goals by the IMO. The green shipping initiated could easily turn to inanity if not financially workable.

Marine industries are highly capital intensive, with high capital expenditures, which require a great amount of financing support. It is necessary to start with money flow to fully utilize the benefits of emission reduction and awareness of climate change [1]. In June 2019, the European shipping financial banking group that provides marine loans for the sake of ESG started to ally with each other to develop the Poseidon Principle (PP) and start a practical emission reduction strategy. Those European financial companies have found that the high demand for loans from marine companies makes operating capital similar to the Greek god, Poseidon, in that they protect their business continuity, and as a result, they ask ship owners and ship manufactories to propose emission reduction strategies or evidence to qualify for favorable loan conditions. The PP requires stakeholders to follow the emission reduction regulation of IMO, not only for the sake of climate change but also for ESG performance.

Climate alignment is defined as the degree of carbon intensity for carriers’ shipping portfolios, and it is in line with a decarbonization trajectory that meets the IMO ambition of reducing total annual GHG emissions by at least 50% by 2050 based on 2008 levels. The PP relies on the annual efficiency ratio (AER) and energy efficiency operating indicator (EEOI) as the carbon intensity metric. The AER uses the parameters of fuel consumption, distance traveled, and deadweight tonnage at summer drought. The EEOI and AER are developed by the IMO to allow shipowners to measure the fuel efficiency of a ship in operation. Standard decarbonization trajectories are produced by the Secretariat of the PP for each ship type and size class in 2020. In the future, any marine company may either supply AER or EEOI when financing is needed.

Global trade is mainly conducted by sea transportation, particularly in the Trans-Pacific (T/P) and Asia–Europe (A/E) regions. As a result, the emission intensity on these two routes is of strong concern. In shipping industries, there are different strategies to reduce the atmospheric concentration of CO₂. This article will focus on container carriers, which apply the deployments of trunk routes, ship-upsizing, speed-limitation, and port selections; these methods can improve energy efficiency and achieve the reduction of CO₂ emissions to the atmosphere, which are application methods of negative emissions technologies (NETs) [2]. This is also the first study to combine the decarbonization trajectory with global shipping finances. The purpose of this paper is to analyze the carbon intensity index under different ship types and sailing operating conditions on main routes (T/P and A/E) and compare the index with the AER/EEOI proposed by PP to understand whether container shipping companies comply with IMO green shipping policy and PP decarbonization trajectory on daily practices or fail to meet the policy.

2. Literature Reviews of Carbon Intensity for Shipping

The issues related to marine pollution and prevention are highly discussed, especially the scope of ship pollution, which has been continuously proposed and focused on by the IMO for years [3]. Among them, two topics, “the transformation technology of emission reduction” and “maritime data standardization”, are specifically listed as important policy directions for future emission reduction in the maritime industry by UNCTAD [4,5]. The first is the discussion of advanced ship-building technology for emission reduction technology. The latter, as shown by the PP, regulates the collection and analysis of emissions data related to various shipping industries.

CO₂ emissions have become a key environmental pollutant that causes climate change in general and global warming [6]. In the scope of “the transformation technology of emission reduction”, the maritime industry must pay more attention to CO₂ emissions. Global shipping companies deploy larger ships with advanced ship-building technology and high fuel efficiency, and the emissions of various pollutants, including CO₂, are also reduced [7]. UNCTAD [4] pointed out that the fleet capacity of container ships increased by more than 45% from 2011 to 2019, while the CO₂ emissions of container ships increased by only 2%. It was obvious that the trend of container ship upsizing has positive benefits for emission reduction since 2000; meanwhile, the annual emissions of each ship have dropped significantly [8]. In addition, this trend of ship upsizing and replacement from the old to eco-friendly ship design is ongoing in the maritime industry [9,10]. However, these improvements are still not enough to meet the total carbon emission reduction target that IMO hopes to achieve in 2050, and more countries are required to make complete technological changes in ship engines and fuels.

According to the normative content of IMO [11] and UNCTAD [4,9], in 2018, IMO member states agreed to “Compared with 2008, an annual greenhouse gas emission rate by 2050 must be reduced by at least 50%.” This is an important part of IMO’s primary strategy to reduce greenhouse gas emissions from ships. To achieve this goal, the shipping financial banking group gathered in Copenhagen on 18 June 2019, and many financial banks unanimously adopted the PP (https://www.poseidonprinciples.org/ accessed on 22 June 2020). This approach was to effectively reveal the investments in the shipping industry by the banking sector to show support for climate change. This was the first time that the banking group incorporated climate change as a factor when giving loans to shipping companies. This action stimulated emission reduction in the shipping industry and met the requirements of the IMO. In the future, PP will become an important indicator to be evaluated by financial institutions when shipping companies of various countries need funding sources. It will also reveal whether major shipping companies are serious enough in the face of climate change.

In addition to the enforcement methods of IMO and countries’ strong regulation of environmental protection, the “carbon tax collection” is also a promotion method. The International Chamber of Shipping, such as BIMCO and other shipping associations, proposes a research and development fund to help reduce pollution [12]. It proposed a carbon price equivalent to USD 0.63 per ton of CO₂ for marine fuel heavy oil and wished that future shipping companies should contribute USD 2 per ton when purchasing marine fuel oil. If the proposal is realized, it will raise approximately USD 5 billion over 10 years for the IMO to promote the development of green shipping globally (Global Maritime Forum) [13].

Moreover, the use of environmental protection as a tax rationale for ocean carbon taxes is increasingly affirmed and acknowledged [14]. The Environmental Defense Fund estimates that in order to achieve at least 50% emission reduction by 2050, which the IMO intends to achieve, or the zero-carbon goal, it costs at least 50 billion to 70 billion USD of capital expenditure per year [15]. The World Bank [16] pointed out that a substantial proportion of such investment opportunities are likely to occur in developing countries terminals, onshore energy infrastructure, and seaport-related equipment. For example, if ships switch oil usage from oil to LNG, ship owners must invest in fleet renewal and modern technologies. On the other hand, onshore filling facilities are also a source of substantial business opportunities [5].

Restrictions on the power of ship engines is another short-term measure to save energy and reduce emissions by IMO. Currently, the various environmental protection practices adopted by practitioners enable ship owners to meet the requirements of the efficiency index of existing ships. It could achieve the target IMO set for 2030. However, limitations on ship engine power reduce the speed of the ship and affect ship performance. One study employed vehicle emission models by the International Council on Clean Transportation to assess engine power limits for “container ships, bulk carriers and oil tankers”. Under different scenarios, it was found that the CO₂ reduction was not proportional to the engine power limit and that the larger ship’s engine did not increase carbon emissions proportionally [17].

The variables affecting ship pollution are complicated, and larger ships have higher total emissions but lower carbon emissions per transport unit because of their larger transport capacity [8]. Small container ships (with a capacity of less than 999 TEUs) have twice the carbon emissions per transport unit as larger ones [10]. Additionally, container ships emit more pollution per nautical mile than dry bulk carriers due to higher sailing speeds. Thus, if we ignore the ship type and ship function, the speed will reflect the coexistence of slow steam and emission reduction benefits, which have been proven in previous studies. The Advanced Maritime Data Analytics on UNCTAD [4] and Marine Benchmark websites in 2019 report that among the annual CO₂ emissions generated by different ship types and ship functions, bulk carriers and container ships rank first and second highest, respectively, in annual carbon emissions, and oil tankers rank third. In addition, because the average sizes of LNG carriers and cruise ships are much larger than those of other offshore vessels, the carbon footprints are much higher than those of small ships.

In decarbonization of the shipping industry survey post by Shell Co. in 2020, ship-building technology and marine engine innovation policies will be the main priorities for IMO to develop green shipping strategies in the future, especially after the COVID-19 pandemic changed the economic structure. The pandemic brought a good opportunity for marine industries to accelerate decarbonization actions in 2020. However, due to the lack of technical coordination and operational awareness between the ship-building industry and the shipping industry, in terms of the use of alternative fuels for ships, in particular, it will be a major obstacle for IMO to implement the decarbonization goal [4]. Except for liquefied natural gas (LNG), hydrogen, ammonia, and other alternative resources are considered to be fuel alternatives; however, because the storage method for power supply is risky and immature, these alternative energies are not yet feasible. Although some shipowners consider the carbon intensity of LNG to be 20% to 25% lower than the current heavy fuel oil, the mining process of LNG is an unpredictable change in GHG emissions; thus, the prospect of LNG used as an alternative fuel in the shipping industry has become uncertain [18].

Finally, ship registration is also one of the important factors that cause the disadvantage of ship emission reduction. The enforcement attitude on the IMO regulation of PSCs and FSCs will have different impacts on emission reduction. It is doubtful that the PSCs and FSCs would adopt appropriate regulations when supervising ships from different nationalities. According to UNCTAD [9], the carbon emissions of ships registered in Panama, Liberia, and the Marshall Islands accounted for 32.96% of the total carbon emissions of the global shipping industry in 2019. The transportation capacity of the top ten ship registration countries accounts for only 48.52% of the global fleet but generates 67.15% of the total global marine carbon emissions. It is obvious that global shipping companies adopt the flag of convenience so that they do not have to conduct green shipping, which is unfavorable for their development.

3. Decarbonization Trajectory and Calculated Model

The purpose of this paper is to estimate the carbon intensity of container ships at trunk routes and verify a suitable estimate model as an indicator for both shipping companies and the financial industry to evaluate. Thus, we propose the decarbonization trajectory value by PP as a reference. Then, we estimate the carbon emissions per unit with container ship sailing activities.

3.1. Reference Datum for Carbon Intensity

The decarbonization trajectory from 2012 to 2050 has been published by IMO (Website of IMO: the Third IMO GHG Study and publication IMO MEPT 68 INF24). These carbon intensity values will vary by ship type, and the estimation criteria and classification will also be updated from time to time. Therefore, PP follows the EEOI and AER traditionally used by IMO as standards. EEOI requires information, including CO₂ emissions, distances sailed while performing transport work, and the amount of cargo (or passengers or GT) carried. This number is the closest measure of the vessel’s true carbon intensity. AER is similar to EEOI but uses an approximation of cargo carried at designed capacity (TEU/GT/Passenger) to replace actual cargo carried and assumes the vessel is continuously carrying cargo; however, ships are not always fully utilized in capacity, and many ships (e.g., tankers and bulkers) operate with ballast voyages, whereas for several voyages a year they have no cargo, this method typically underestimates carbon intensity (https://www.poseidonprinciples.org/ on 22 June 2020).

It is uncertain whether EEOI or AER should be used, as these standards require different indicators for estimation. For example, we take a container ship with a capacity above 14,500 TEUs, as an example in

Table 1. The Decarbonization Trajectory of the Poseidon Principle.

Container Ship (TEU Convert to GT)	2012 Median EEOI/AER		2019 AER Trajectory Value	2020 AER Trajectory Value	2021 AER Trajectory Value
0–999 TEU	34.60	21.40	18.10	17.70	17.20
1000–1999 TEU	31.60	18.80	15.90	15.50	15.10
2000–2999 TEU	24.70	12.65	10.70	10.40	10.20
3000–4999 TEU	21.30	10.52	8.90	8.70	8.40
5000–7999 TEU	20.50	9.94	8.40	8.20	8.00
8000–11,999 TEU	17.90	8.47	7.20	7.00	6.80
12,000–14,500 TEU	13.20	5.87	5.00	4.80	4.70
14,500 TEU +	13.20	5.87	5.00	4.80	4.70

Unit: CO_2e g/t-nm. Resource: https://Poseidon Principle, 22 June 2022. [1].

and convert TEUs to gross tonnage (GT). The carbon intensity per nautical mile was 13.2 (g/t-nm) according to the EEOI standard value in 2012. However, the annual standard value of AER from 2012 to 2021 is 5.87–4.70 (g/t-nm), which shows that the AER value was much lower than the EEOI value. The research results of this paper will use the AER values in Table 1 as the reference for the following discussion [1].

3.2. Model Design of Carbon Intensity for Container Shipping

Activity-based methods are used to combine the total amount of pollutant emissions from various stages of actual operation with container ships deployed on the trunk route by carriers. Previous research has used this method, but variables were different depending on a wide range of voyage routing, vessel size, and fuel type. We examined the literature and practical experience presented by [7,8,19,20,21] and found that this research method can effectively estimate the pollutant emissions of vessels sailing with different ship types and routes to combine the total amount of pollutant emissions from various stages of actual operation container ships. This paper lists all the items used to make various calculations presented in this research in

Table 2. Symbols and explanations.

Symbol	Explanation
$P^e$	The sum of all CO2e (including CO2, CH4, N2O) by a vessel under different speeds and during berthing, unit: ton.
$P_{Sailing}^e$	Total pollution of CO2e generated during sailing, unit: ton.
$P_{Manoevring}^e$	Total pollution of CO2e generated during the maneuvering stage when the container ship slows down upon approaching the port, unit: ton.
$P_{Port}^e$	Total pollution of CO2e by a container ship docked and loading/unloading stage at a port, unit: ton.
$Tim{e}_{Sailing}$	Time for a container ship to sail from Port i to Port j (unit: hours). Calculated by dividing Di~j by V.
$Tim{e}_{Manoevring}$	Time required by a container ship to maneuver its way into a port, including waiting time for a berth. Port authorities estimate each vessel to spend approximately 2–5 h maneuvering at each port, unit: hours.
$Tim{e}_{Port}$	Operation time while berthing at each port, which is determined by the operation efficiency of each port.
$D_{i~j}$	Distance from Port i to Port j (unit: nautical mile).
$V$	Vessel speed (unit: knot, nm per hour). Vessel speed is determined by power from the propeller, but actual speed may be affected by many factors. The optimum speed for the entire voyage is set from V = 15 to V = 20 knots.
$Q_i$	Total operation volume (TEU) at Port i, including loading/unloading. The estimated volume is based on the proportion of ship capacity.
$E{F}_i$	Operational efficiency at Port i. According to port authorities, most port operators use four or more gantry cranes to handle a trunk-route ship. The hub ports such as Shanghai and Singapore can handle 160 TEU per hour; other ports can handle 135 TEU per hour on average.
$F_t^o$	Fuel economy: including various fuels used by the main engine, such as heavy diesel (HO) and generator oil (DO). t denotes the vessel type. The authors of [22] show the below values: The F value of HO: F = 0.5489×e0.107*V for large containerships (t = above 10,000 TEU; R2 = 0.9970), F = 0.4614×e0.1025*V for containerships (t = 3800–9999 TEU; R2 = 0.9959), and F = 0.3501×e0.1115*V for containerships (t = 999–3799 TEU; R2 = 0.9983). The F value of DO: F = 0.063 tons/per hour (t = above 10,000 TEU), F = 0.087 tons/per hour (t = 3800–9999 TEU), and F = 0.091tons/per hour (t = 999–3799 TEU).
$K_n^o$	Emission factor (unit: ton/fuel type-ton weight) emitted during sailing (KHO = 2.6617 tons; KDO = 2.5212 tons), maneuvering (KHO = 2.6829 tons; KDO = 2.6743 tons), or berthing (KDO = 2.6743 tons). o refers to the type of fuel (HO/DO), n refers to sailing, maneuvering, and berthing [22].

.

When estimating the pollutant emissions from vessels, we calculate $F_t^o$ first, which represents the amount of hourly fuel consumption with different ship types and speeds. This research considers that the container ship uses heavy oil (HO) and diesel oil (DO) as the fuel sources during its voyage but uses DO only for an auxiliary power generator when the main engine is shut off during berthing at port. We have examined studies by [22,23,24] and compiled the fuel economy formula. After that, we calculate $K_n^o$, which stands for the coefficient of the total amount of pollutants generated per fuel unit (ton) burned when the ship is sailing, maneuvering, and berthing. The estimates of CO_2e under different scenarios in Table 2 have been confirmed [22].

The carbon intensity P^e is the total carbon emission amount of a vessel with different sailing stages. The total carbon emission refers to the sum of the emission amount during sailing ($P_{sailing}^e$) plus berthing at the port, which includes the emission amount during maneuvering ($P_{maneuvering}^e$) and loading/unloading at the port ($P_{port}^e$). A container ship emits different amounts of pollutants during sailing, maneuvering, or berthing at the port, so the amount for each stage needs to be added together, as shown in Formula (1) as follows:

$$P^e=P_{Sailing}^e+P_{Manoevring}^e+P_{Port}^e$$

(1)

Formula (2) calculates the emission amount during the sailing stage by multiplying the sailing time (divide distance by vessel speed) by the fuel economy (F value) and the emission factor (K value).

$$\begin{array}{c}{P}_{Sailing}^e=Tim{e}_{Sailing}\cdot F_t^o\cdot K_{Sailing}^o\\ =\left(\frac{D_{i~j}}{V}\cdot F_t^{ho}\cdot K_{Sailing}^{ho}\right)+\frac{D_{i~j}}{V_{}}\cdot F_t^{do}\cdot K_{Sailing}^{do}\end{array}$$

(2)

Formula (3) calculates the emission amount during the maneuvering stage. A container ship usually slows down when approaching a port by multiplying the time required for maneuvering by the F value and the K value.

$$\begin{array}{c}{P}_{Manoevring}^e=Tim{e}_{Manoevring}\cdot F_t^o\cdot K_{Manoevring}^o\\ =Tim{e}_{Manoevring}\cdot (F_t^{ho}\cdot K_{Manoevring}^{ho}+F_t^{do}\cdot K_{Manoevring}^{do})\end{array}$$

(3)

HO is not consumed when a container ship docks at a port; burning diesel (DO) is still necessary to power the ship generator to support basic electricity on the boat; therefore, less carbon emissions are generated in port. In Formula (4), the vessel berthed at the terminal time ($Tim{e}_{Port})$ is equal to the estimated workload at port ($Q_i$) divided by the terminal loading and unloading efficiency (EF).

$$P_{Port}^e=Tim{e}_{Port}\cdot F_t^o\cdot K_{Port}^o=\frac{Q_i}{E{F}_i}\cdot F_t^{do}\cdot K_{Port}^{do}$$

(4)

4. Trunk-Route Setting and Pollutant Assessment Results

4.1. Containerized Trade on Major East–West Trunk Routes

Global trade is mainly conducted by sea transportation; as UNCTAD [25] stated in 2020, the Trans-Pacific (T/P), Asia–Europe (A/E), and Trans-Atlantic (T/A) are the three major routes, accounting for more than 39.7% of global trade. In 2021, the trade volumes of T/P, A/E, and T/A were 31.2, 26.3, and 8 million TEUs, respectively, reaching their highest values in ten years. Currently, global container carriers deploy mega containers on T/P and A/E. Consequently, the emission intensity on these two routes is of extreme concern.

In this article, T/P and A/E were studied because these two voyage routes generate the largest amount of emissions due to the greatest number of container companies involved, the largest ship size, the highest cargo capacity, and the maximum trade volume delivered, as

Table 3. The capacity of container alliance and carriers on East–West trunk routes.

Capacity of Global Container Alliance and Carriers (TEUs)			On Asia–Europe Weekly Capacity (A/E)	On Asia–North America Weekly Capacity (T/P)
Global Capacity of Containerships deployed (TEUs)	25,215,883	100.00%	100.00%	100.00%
2 M Alliance (Maersk+MSC)	8,599,614	34.10%	36%	25%
OCEAN Alliance (EMC+CMACGM+COSCO)	7,725,128	30.64%	36%	37%
THE Alliance (Hapag-Lloyd+YML+HMM+ONE)	4,752,193	18.85%	26%	23%
Other shipping carriers	4,138,948	16.41%	2%	15%
Averaged TEU Size Range of Ships before Oct 2020.			13,000–24,000	4000–14,000
Averaged TEU Size Range of Ships after June 2022.			10,000–24,000	1700–16,000

Resource: Alphaliner Monthly Monitor, June 2022 [26].

shows. In May 2022, the global container capacity reached 25,215,883 TEUs, of which the top nine container companies accounted for 83.59% of the capacity. These nine companies assemble three alliances (2 M/OCEAN/THE). The market share of these three alliances accounts for 98% of A/E and 85% of T/P. It is noted that after 2020, because of the long-term effect of COVID-19, port congestion occurred in many container ports of trunk routes, and container carriers deployed more diverse types of small ships to increase revenues and seize the opportunity for freight rate growth. These situations may cause more pollution emissions from vessels.

As shown in Table 3, on the A/E route, since ship size is not restricted to the Panama Canal, 24,000 TEU-size ships are workable. However, in June 2022, the size shrinks to 10,000 TEUs in the same route, while the size decreases to 1700 TEUs in the T/P route. Smaller vessels generate more emissions, as UNCTAD [10] confirmed that small vessels create more emissions per unit than larger vessels.

As Figure 1 shows, we select three primary routes, Route A (A/E Trunk Routes), Route B (Asia–USWC Trunk Routes) and Route C (Asia–USEC Trunk Routes), to calculate the carbon intensity.

Table 4. Calling ports and ship size range on route A/B/C.

Port	Route A: Asia–Europe Trunk Routes	Route B: Asia–USWC Trunk Routes	Route C: Asia–USEC Trunk Routes
1	Busan	Singapore	Singapore
2	Qingdao	Yantian	Yantian
3	Shanghai	Shekou	Xiamen
4	Ningbo	Xiamen	Ningbo
5	Hong Kong	Hong Kong	Shanghai
6	Xiamen	Ningbo	Qingdao
7	Shekou	Shanghai	Busan
8	Yantian	Qingdao	Colon
9	Singapore	Busan	Savannah
10	Port Kelang	Tacoma	NY/NJ
11	Piraeus	LA/LB
12	Hamburg
13	Rotterdam
Scenario changes	Ship-size Range: Route A	Ship-size Range: Route B	Ship-size Range: Route C
	11,300–24,000 TEU	8194–16,020 TEU	4398–13,092 TEU
	None	1708–7241 TEU for scenario changes: Route B-1/Route B-2/Route C-1

specifies the sequence of port calls and the ship size (11,300–24,000 TEU; 8194–16,020 TEU; and 4398–13,092 TEU) that were deployed in these three routes.

In addition, after the 2020 COVID-19 pandemic, because container freight rates rose sharply, many well-known medium-sized container carriers, such as Wan Hai/CU-Line/Zim and others, have also deployed smaller ships to enter the T/P market and increase revenue. Many carriers must respond to the serious port congestion on trunk routes and the changes in vessel type used, which may also lead to increased emissions. Considering these real scenarios of port congestion and ship downsizing on the T/P route, Route B-1 simulated the situation of the Asia–USWC trunk route in which ships must wait for two weeks to enter the port of LA/LB ports after 2020, and Route B-2 further simulated the situation of the downsizing trend of ship size use after 2020. Route C-1 simulates the case of the Asia–USEC trunk route with small-size ship deployment without port congestion.

4.2. Assessment Results of Carbon Intensity

According to the various scenarios stated in 4.1, we calculated different carbon intensities in each main container shipping route, as

Table 5. Carbon Intensity on Different Trunk Routes and Scenarios.

Route A		Route B		Route B-1		Route B-2		Route C		Route C-1
Ship-Size	Value *	Ship-Size	Value *	Ship-Size	Value *	Ship-Size	Value	Ship-Size	Value *	Ship-Size	Value
11,300	6.48	8194	9.88	8194	9.92	1708	47.56	4398	18.34	1708	47.20
13,300	5.50	8850	9.15	8850	9.19	2824	28.77	5466	14.76	2824	28.55
13,800	5.31	8888	9.11	8888	9.15	4132	19.66	5527	14.59	4132	19.52
14,000	5.23	9962	8.13	9962	8.16	4178	19.45	6724	12.00	4178	19.30
15,300	4.79	10,036	8.07	10,036	8.10	4713	17.24	6845	11.78	4713	17.11
17,800	4.12	10,888	7.44	10,888	7.47	7241	11.22	6966	11.58	7241	11.14
18,000	4.07	11,008	7.36	11,008	7.39			7024	11.48
19,400	3.78	11,388	7.11	11,388	7.14			8189	9.86
20,500	3.58	12,118	6.68	12,118	6.71			8501	9.49
22,000	3.34	13,568	5.97	13,568	5.99			9466	8.52
22,690	3.24	14,812	5.47	14,812	5.49			11,008	7.33
23,000	3.19	15,000	5.40	15,000	5.42			12,118	6.66
24,000	3.06	16,020	5.06	16,020	5.08			13,092	6.17

* 2012–2019 AER trajectory value: refer to Table 1. Route A: Asia–Europe Trunk Routes; Route B: Asia–USWC Trunk Routes; Route B-1: Asia–USWC Trunk Routes with port congestion; Route B-2: Asia–USWC Trunk Routes with port congestion and ship-downsizing; Route C: Asia–USEC Trunk Routes; Route C-1: Asia–USEC Trunk Routes with ship-downsizing; Ship-size: TEUs; GT (ton)/TEU = 7.5 for Full Container Ship. Value: CO_2e g/ton-nm.

shows. These values are affected by the variables in Table 2, especially the operational efficiency of the terminals and the fuel economy. All carbon emissions are estimated with some errors. However, through a literature review [6,22], the values derived from this method are credible. We compared the results with the data shown in Table 1, and the conclusions are as follows.

Route A: There are thirteen port calls along the A/E trunk route from Busan to Rotterdam, run by 11,300–24,000 TEU container ships. The results show that the value of carbon intensity decreases from 6.48 to 3.06 g/ton-nm as the ship size increases. Figure 2 shows that the larger the container ship size is, the lower the carbon emissions per unit during a voyage. The AER value ranged from 6.80 to 8.47 g/ton-nm for the 8000–11,999 TEU ship from 2012 to 2021, as Table 1 shows. Taking the 11,300 TEU ship size in Table 5 as an example, the AER value is 6.48 g/ton-nm and is lower than 6.80 g/ton-nm. It is concluded that all ship size allocations on the A/E trunk route comply with the decarbonization trajectory proposed by the PP, as Figure 2 shows.

Route B: There are eleven port calls along the Asia–USWC trunk route from Singapore to the port of LA/LB, run by 8194–16,020 TEU container ships. The results show that the carbon intensity decreased from 9.88 to 5.06 g/ton-nm as the ship size increased. Figure 3 shows that the larger the container ship size is, the lower the carbon emissions per unit during a voyage. The AER value ranged from 4.70 to 8.47 g/ton-nm for the 8000⁺ TEU ships from 2012 to 2021, as Table 1 shows, but only ship sizes above 9962 TEU had an AER value of 8.13 g/ton-nm, which was lower than 8.47 g/ton-nm. It is concluded that only ship sizes above 9962 TEU deployed on the Asia–USWC trunk route comply with the decarbonization trajectory proposed by the PP, as Figure 3 shows.

Route B-1: This scenario assumes that two more weeks are awaited outside the port of LA/LB because of port congestion, and similar to Route B, the carbon intensity slightly decreases per unit when the ship size increases, from 9.92 to 5.08 g/ton-nm. This shows that most ships running on the Asia–USWC trunk route complied with the decarbonization trajectory proposed by the PP, as Figure 4 shows.

Route B-2: This scenario assumed that in addition to two more weeks awaited outside the port of LA/LB because of port congestion, container carriers deploy small-size ships (1708–7241 TEU) to boost revenue. The result shows that when the ship size decreases, the carbon intensity increases dramatically (47.56 g/ton-nm for a ship size of 1708 TEU). In Table 5, the AER values of ship sizes between 1000 and 7999 TEU are 47.56 to 11.2 g/ton-nm, much higher than the 18.80 to 8.00 g/ton-nm in Table 1. Figure 5 shows that all ship sizes do not comply with the decarbonization trajectory proposed by PP, which indicates that the deployment of small ships on the Asia–USWC route is not eco-friendly.

Route C: There are fewer than ten port calls along the Asia–USEC trunk route from Singapore to the port of LA/LB, run by 4398–13,092 TEU container ships that are allowed to pass the Panama Canal. The results showed that the carbon intensity was between 18.34 and 6.17 g/ton-nm for all ship sizes. From Table 1, ship sizes above 8000 TEU have AER values between 4.70 and 8.47 g/ton-nm. In Table 5, ship sizes above 11,008 TEU have an AER value of 7.33 g/ton-nm, and Figure 6 shows that this result complies with the decarbonization trajectory proposed by PP.

Route C-1: This scenario was similar to Route B-2; container carriers deploy small-size ships (1708–7241 TEU) to boost revenue on the Asia–USEC route. The results showed that the AER value reached 47.20 g/ton-nm for a ship size of 1708 TEUs. In this scenario, the carbon intensity is much higher than the data in Table 1, which indicates that the deployment of small vessels on ocean routes is short-sighted behavior and not eco-friendly (in Figure 7).

5. Conclusions

As of 2021, 18 leading shipping financial banks, jointly representing approximately more than USD 150 billion in loans, equivalent to 30 percent of the global amount, have come together to establish the PP (https://kknews.cc/world/x4eao4g.html, accessed on 22 June 2020). The marine industry is complex with numerous industry classifications; there are more than fifty kinds of offshore vessels. However, presently, the PP was designed primarily for regulating container shipping carriers, bulk carriers, and crude tankers. It is comprehensible that there is a gap between the marine and banking industries in terms of decarbonation trajectory standards.

In this article, an emission reduction model with limitations for container carriers was built and subject to many vessel operation variables with terminal conditions, and carbon intensity was calculated based on different routes/ships allocated by leading container carriers. According to the A/E and T/P trunk routes and ship strategies by major container carrier alliances, it is shown that in the trend of vessel upsizing, the carbon emissions per unit of each ship are decreasing to a greater extent than UNCATD stated [10].

Based on the PP trajectory, it is also shown that almost ultra-large container vessels only (18,000 TEUs above) are deployed on the A/E trunk route, which coincides with the EEOI/AER decarbonization trajectory. It is worth noting that starting from 2020, due to the COVID-19 pandemic, shipping companies deployed a higher number of small-size containers to boost revenues, resulting in more pollutant emissions and a mismatch of the decarbonization trajectory on the T/P trunk routes.

The shipping industry is highly capital intensive, and it is necessary to start with money flow to fully exploit the benefits of emission reduction and the wariness of climate change. Nevertheless, financial banking industries are not able to go deep into practical operations in shipping industries. This article disclosed a feasible model to calculate the exact carbon intensity and decarbonization trajectory for future implications.