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1 INTRODUCTION
Changes in the Earth's overall climate system indicate
global climate change. These changes are manifested
by effects such as temperature increase, melting of
glaciers and abnormal weather events. Especially the
developments following the industrial revolution have
resulted in the global warming we are experiencing
today. Global warming refers to the change in surface
temperature relative to a baseline value. Data from
1850-1900 are accepted as the basic value. Because it is
accepted that there are no reliable observations from
earlier periods. Human-induced greenhouse gas
emissions are seen as the main reason for this change.
Some of the sun's rays that strike the earth and are
reflected back into space become trapped by
greenhouse gases in the atmosphere. This process,
where radiation emitted from the earth is captured by
greenhouse gases like Carbon dioxide (CO₂), Methane
(CH₄), and Nitrous oxide (N₂O), is referred to as the
greenhouse effect [1]. Since the 1750s, particularly due
to the industrial revolution, emissions of these gases
have been on the rise [2]. The concentration of CO2, the
most significant greenhouse gas, increased from
around 280 ppm (parts per million) during the pre-
industrial era to 407.96 ppm by March 2018; similarly,
the level of CH4, which was approximately 715 ppb
(parts per billion) in the pre-industrial era, rose to 1859
ppb by the end of 2017; the global atmospheric
concentration of N2O also climbed from about 270 ppb
in the pre-industrial period to 330 ppb in 2017 [2].
The transportation sector has an important role on
the formation of the greenhouse gas effect.
Approximately 20% of global emissions from human
Reducing Carbon Emissions in the Maritime Sector
for a Green Transition: Current Status and Future
Perspectives
M. Saka
Piri Reis University, Istanbul, Turkey
ABSTRACT: Vessels carrying goods in global trade produce approximately 3% of global greenhouse gas (GHG)
emissions. To reduce or even eliminate this contribution caused by ships, studies are being conducted on
alternative fuels and new technologies to replace fossil fuels. The International Maritime Organization (IMO),
which coordinates the maritime sector's activities at the international level, has set targets and implemented
various regulations in this direction. These targets set by the IMO are actually challenging targets for maritime
transportation operators. Beyond the need for technological advancement, they also require significant resource
allocation from an economic perspective. This study describes the current situation and measures taken on GHG
emissions from the Maritime Sector and provides an overview of the means that can be used to achieve the targets.
The results of the study show that there are various alternatives that can substitute fossil fuels, but technological
developments are needed for their widespread use. However, the solutions expected are both financial and
technical. It is assessed that the industry's practical capacity for green transformation is not yet aligned with IMO's
regulations, and a multi-actor, coordinated approach is needed to achieve this.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 20
Number 3
September 2026
DOI: 10.12716/1001.20.03.12
642
activities come from the transportation sector [3]. The
energy used for transportation to a large extent is
obtained by fossil fuels. The International Maritime
Industry, which transports 80% of world trade [4], has
a significant impact in this respect. It is estimated that
approximately 2% to 3% of global carbon emissions are
caused by maritime transportation activities, and
approximately 11% of emissions from global
transportation [5, 6]. Carbon emissions within
maritime transport heavily relies on fossil fuels [7]. The
ratio of CO2 emissions from ships to global greenhouse
gas emissions is approximately 2% [8, 9], this amount
accounts for at least 90% of the CO2 emissions for
which the maritime sector is responsible [5]. Therefore,
the maritime sector needs to take measures in line with
the green transition target [10].
2 MATERIALS AND METHODS
The current study employs a qualitative synthesis
method ordered under principles of policy analysis
and technology assessment that are excellently utilized
in maritime transition studies. The study rigorously
analyzes regulatory codes, technical documents, and
global strategy reports to infer an ordered
understanding of the maritime industry's
decarbonization trajectory.
2.1 Identification of the Data Source
Primary regulatory data were obtained from IMO
Strategy Documents, MEPC resolutions, EEDI/EEXI
implementation guide, and CII/DCS data framework.
These official sources were complemented with peer-
reviewed scholarly papers, engineering case studies,
and class society technical reports from organizations
such as DNV (Det Norske Veritas). Selection was on the
basis of credibility, relevance to IMO 2018–2023 climate
agenda, and coverage of both regulatory intent and
technology viability.
2.2 Policy Mapping Approach
A policy mapping exercise was conducted to transform
the development of maritime emission regulation from
the international obligation of the Kyoto Protocol
assigned to IMO to the 2023 GHG Strategy. The
mapping was used to define degrees of regulatory
ambition, intermediary emission reduction aims, and
compliance measures that include EEDI, SEEMP, EEXI,
CII, and data-driven tools such as DCS.
2.3 Technology Readiness and Feasibility Scanning
A systematic model of technology scanning was
employed to cluster existing and future
decarbonization technologies into four categories:
− Design efficiency technologies (hull optimization,
air lubrication, etc.),
− Hybrid and propulsion systems,
− Alternative fuels (hydrogen, ammonia, methanol,
LNG, biofuels), and
− Carbon capture and renewable support systems
(CCS, rotor sails, photovoltaic support).
Every technology was assessed in terms of
decarbonization potential, Technology Readiness
Level (TRL), limitations for implementation,
infrastructure needs, and economic affordability to
differently capitalized shipowners.
2.4 Comparative Synthesis Framework
In the last step, a comparative synthesis was carried
out. This was a synthesis that revealed whether
regulatory rules and targets, such as the net zero target,
were compatible with technological capabilities and
the limitations of the sector. This synthesis highlighted
areas of mismatch of policy aspirations with existing
technological readiness and cost feasibility.
The general methodological framework employed
in the current research is illustrated in Figure 1,
showing the conceptual connection between the IMO
regulatory framework, technological solutions,
operational practices, and the resulting sectoral
impacts in maritime decarbonization.
Figure 1. Summary of the methodological flow.
The sources consulted addressed maritime GHG
emissions reduction policies‚ mitigation technologies
and alternative fuels‚ as well as implementation
considerations․ Sources that concerned only general
climate change information or non-maritime
applications were not included in the technology
assessment․ The selected technologies were compared
regarding emission reduction potential‚ technology
readiness‚ existent infrastructure‚ implementation
issues‚ and economic factors. The criteria were
designed to analyze technologies at different levels of
readiness and do not establish a ranking regarding the
technologies.
3 RESULTS
3.1 International Policies and Regulations
The Kyoto Protocol, which came into effect in 2005 and
imposed GHG reduction obligations on the countries
party to the agreement, has gone down in history as a
first in terms of global climate policies. As being the
first international agreement aimed at reducing GHG
emissions, it imposed responsibility to the IMO and
International Civil Aviation Organization (ICAO) for
the control of emissions from both maritime and air
transportation within the scope of global
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transportation [11]. Since it contains provisions for the
reduction of greenhouse gas emissions from shipping,
it was discussed in the relevant committees of IMO for
the measures to be taken [12]. In fact, IMO started to
take responsibility for the reduction of maritime
emissions since 1997, when the Kyoto protocol was
published.
IMO's steps on this issue are summarized in Table 1
according to their historical development. IMO, which
is authorized and responsible for this issue, published
its first "Greenhouse Gas Study" report in 2000. This
report, which deals with CO₂ emissions from ships in
detail, revealed that emission rates vary depending on
ship types and fuel utilization.
Table 1. Historical development of measures taken by IMO.
Year
1997
2000
2008
2011
2018
2023
The IMO Marine Environment Protection
Committee (MEPC) developed two technical means of
the greenhouse gas reduction in 2008. The first means
is the EEDI (Energy Efficiency Design Index), which
attempts to induce the fitting of energy-efficient ship
engines and equipment [13]. EEDI is an indicator of the
ship's energy efficiency, with the ratio of the ship's
potential ship CO2 emission and its commercial
freight-carrying capacity [14]. It establishes a minimum
energy efficiency level per capacity mile for ships by
type and size. Ship Energy Efficiency Management
Plan (SEEMP) is an on-board management tool to
minimize the cost of energy consumption by the ship
[5]. These are the first formal means of assessing and
managing ship design and operating carbon saving
potential.
IMO introduced EEDI and SEEMP as regulatory
laws in 2011. EEDI is a regulation that makes carbon
efficiency mandatory for new ships. This application,
which entered into force in 2013, was planned to be
implemented in three stages after the initial phase
where the reference level was accepted. In determining
the EEDI reference values, which aim to determine the
minimum efficiency of new ships, the emission data of
commercial ships built between 2000-2010 were
utilized in accordance with MEPC Resolution 231(65),
which entered into force in 2013. EEDI Reference Value
was calculated separately for each vessel type. A
summary of all phases of the EEDI is provided in
Table 2.
For new ships, in the first phase, the EEDI value was
required to be at least 10% lower than the reference
values. In the second phase, this improvement rate was
required to be at least 20%. In the last phase we are in,
an improvement of at least 30 per cent compared to the
reference values, and even up to 50 per cent in some
ship types (such as container vessels), is required. In
addition to the expected improvements in the EEDI
value, a shift towards advanced technologies is
encouraged. As it is understood from these
explanations, a lower CO₂ emission design obligation
has been introduced for new ships in each phase. This
progressive system encourages continuous
improvement of shipbuilding technologies and a focus
on energy efficiency.
Table 2. Summary of EEDI phases.
Phase
Period
Intended EEDI
Improvement
Explanation
0
2013–
2015
Reference level
As a result of the measurements,
reference levels were determined
for ship types.
1
2015–
2019
%10 reduction
EEDI implementation started,
newbuilding vessels limited
2
2020–
2024
%20 reduction
Efficiency requirements
tightened
3
2025+
%30 reduction (up to
50% for some types)
Advanced technologies
encouraged, minimum carbon
emissions targeted
3.1.1 Adaption of Initial IMO GHG Strategy
Initial IMO GHG Strategy was adopted in 2018. This
comprehensive climate action plan included targets to
cut down in carbon intensity 40% and 50% by 2030 and
2050 respectively. 2008 values would be taken as
reference for these targets. Beyond these targets, as a
longer-term goal, a vision of net zero emissions by 2100
was put forward.
In the subsequent process follow-up, "Data
Collection System (DCS)", utilized for the
measurement of carbon emissions, has been amongst
the key innovations used in the Maritime sector
pursuant to the energy efficiency objective. DCS stands
for data collection system through which annual fuel
oil usage and CO₂ emissions are reported by ships.
According to obligatory practice adopted by IMO in
2016 and executed under MARPOL Annex VI; with
effect from the calendar year 2019, all vessels of 5,000
gross tonnage and above are to report the same on the
basis of methodology described in SEEMP [15-17]. The
purpose of this system, requiring reporting of fuel
consumed, power and type of engine, distance and
time (active cruise time), CO₂ emissions, gross tonnage
and cargo carried, is to publicly report fuel
consumption, emission, and energy efficiency data
caused by maritime transport. The data presented by
the companies must be accepted by the administration
according to procedures and then exported to the Ship
Fuel Oil Consumption Database established by IMO
[15]. It serves as the data repository for IMO's climate
policy and regulation. Carbon Intensity Indicator (CII)
was derived from this kind of fuel use, distance and
voyage time data like pulled out of DCS and applied
towards operational level world policymaking.
Median regression analysis on ship profiles for the
period 1999-2009 was based on DCS data and yearly
CO₂/tonne-mile performance (CII) was computed. The
findings based on the DCS data provided guidance on
what carbon reduction should be tackled first for
which segments. Levels of CII as of 2023 were
categorized as A–E and the requirements that each of
these has to meet have been explained [18]. According
to the results of DCS data analysis, it was established
that LNG carriers and container vessels are the most
CO₂-intensive ship types. The containership fleet is
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estimated to account for 25% of total ship fuel
consumption [19].
In addition to the measures announced for
newbuilding ships in IMO's 2018 strategy, some short-
term measures have also been introduced to reduce
GHG emissions and improve energy efficiency of
existing ships. In addition to the CII, the Energy
Efficiency Existing Ship Index (EEXI) is also among the
tools that will become mandatory from the beginning
of 2023.
EEXI is a measurement of a ship's energy efficiency
performance relative to a point of reference [17, 20].
The purpose of the EEXI is to help decrease CO2
emissions of the existing (older) vessels [21]. According
to IMO [20], vessels are required to calculate their
achieved EEXI and compare achieved EEXI with
required EEXI using the reduction factors applied by
regulation relative to the EEDI baselines. To achieve
the level of energy efficiency, each vessel will have a
calculated attained EEXI that is below the required
EEXI.
In 2023, IMO revised its GHG strategy in the MEPC
80 meeting, where it has made its climate ambition
more ambitious. The new strategy clearly stated the net
zero emissions target by 2050 and set intermediate
targets for 2030 and 2040 [12, 22]. Resolutions were also
made to develop tools such as carbon pricing,
alternative fuel incentives, and more stringent
CII/EEDI requirements. This update shows that IMO is
getting closer to Paris Agreement goals.
In the Third IMO GHG Study carried out in 2014
using data from 2012, shipping GHG emissions were
estimated to be about 2.2% of global production, while
in the Fourth IMO GHG Study that was carried out in
2020 and used 2018 data, the percentage was set at
about 2.89%. Such findings had shown that IMO was
behind when it came to GHG goals.
3.1.2 2023 GHG Strategy
Considering the necessity of taking greater drastic
measures, IMO has set 2023 GHG Strategy goals as
follows [12]:
− To strengthen IMO's contribution to the
international struggle against greenhouse gas
emissions,
− To make decisions regarding measures the world's
shipping transport must undertake and to make
recommendations
− To enable research and tracking of GHG emissions
from shipping so that the objectives can be achieved
and the measures needed to improve it identified.
The objectives below are in IMO's 2023 strategy:
− Development of new ship designs to reduce carbon
intensity,
− By 2030, cut down ship emissions by a minimum of
40% at regard of the 2008 levels,
− By the year 2030, the sector should aim to have at
least 5 percent of its energy needs met by
technologies that produce zero or nearly zero
greenhouse gas emissions, with an extra target
towards 10 percent,
− Strive to reach net zero emissions in maritime
transport by 2050 while continuing to work towards
the goals outlined in the Paris Agreement.
It was also decided in 2023 that the IMO GHG
Strategy will be reviewed every five years, and the first
review will take place in 2028.
3.2 Current Technologies for Emission Reduction
In order for policies and regulations drafted to reduce
anthropogenic GHG emissions to succeed in a
significant manner, they must be supplemented by
technical innovation. The majority of innovative
solutions developed within the shipping sector during
the recent past offer significant contributions towards
reducing fuel consumption and carbon emissions.
These technologies can generally be divided into four
main categories: ship design, energy efficiency
systems, operational optimizations, and digitalization
applications [23, 24].
3.2.1 Energy Efficiency Innovations in Ship Design
There are various innovations that increase energy
efficiency regarding ship designs. With regard to ship
design, Seo et al. [25] executed a study about the effect
of the concept of Curved Keel Hull, which facilitates
the use of a larger propeller diameter, for a 3600 TEU
container ship. They calculated that the application of
a keel inclination of 0.35 degrees can save more than
5% shaft power.
Some improvements are also possible regarding the
ship's friction resistance. It is stated in the literature
that if the low-friction hull coating method is used as a
precaution against energy loss caused by friction, a fuel
consumption saving of up to 4.5% can be achieved [26].
Hull air lubrication refers to the creation of an air
layer between the ship's hull and seawater in order to
bring down the hull resistance [25]. The reduced
resistance in the ship's hull also leads to reduced fuel
consumption. In a computational analysis, Fotopoulos
and Margaris [27] calculated that fuel savings of up to
8% could be possible on a ship through the application
of air lubrication. As a result of their studies on three
different concepts called air bubble, air layer, and air
cavity, Fotopoulos and Margaris [27] found that the
most efficient concept would be the air cavity concept,
which is applied by injecting air into a recess or space
under the hull, with savings of 16 to 22%.
The literature also includes reviews and modelling
of hybrid implementation. Asus et al. [28] examined
the Hybrid application alongside an internal
combustion engine and found that this Hybrid solution
could reduce fuel consumption by approximately 30%
compared to a system that relies solely on an internal
combustion engine. Geertsma et al. [29], who stated
that the mechanical propulsion system is more efficient
starting from 80% of the ship's design speed in the
classical mechanical propulsion system, estimated that
fuel consumption could be saved up to 20% with the
hybrid system. They also stated that the hybrid system
is more beneficial in case of cruising for a long time
below 40% of the maximum speed.
The Energy Efficiency Design Index (EEDI), for
which the IMO introduced a requirement back in 2011,
is the first global regulation to express energy
efficiency performance in quantifiable terms for new
ships and has encouraged ship designs to produce
lower carbon intensity vessels [5].
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3.2.2 Auxiliary Energy Systems and Alternative
Supporting Technologies
Some support energy systems, which can be
integrated with the current ship systems, also
contribute to reducing emissions. Waste heat recovery
systems, for example, enable energy from exhaust
gases to be used to generate onboard electricity. These
systems reduce both energy usage and emissions.
Analyzing the energy system of a chemical tanker,
Baldi et al. [30] particularly emphasized the potential
of recovering waste heat from exhaust gases and stated
that the exergetic value of the waste heat represented
18% of the engine power output.
The use of wind technology in reducing carbon
emissions is also among the topics being researched.
Sail-assisted drive units (e.g. rotor sails, wing-in-
ground effect) and solar panels are additional features
to reduce consumption of fossil fuels. Traut et al. [31],
who studied the numerical performance of a Flettner
rotor and a towing kite, determined that both methods
would provide CO2 savings. They determined that fuel
savings could be between 2-24% with a single Flettner
rotor, and between 1-32% with a towing kite.
3.2.3 Operational Optimization
Optimizations at the operating level also play a big
part in reducing emissions. The cruise at low-speed
technique known as “slow steaming” plays a beneficial
role in terms of emissions by decreasing fuel usage
directly.
A wide range of studies have been realized in recent
times that reducing the speed of ships in maritime
transportation will also reduce GHG emissions, and
the results of these studies have also been passed into
the literature. Within the scope of these studies, it is
seen that if the speed of container ships, which cause
the most intense GHG emissions in global maritime
transportation, is halved, it is possible to save up to
70% of CO2 emissions [32]. However, due to such
practice, costs will increase due to the decrease in the
amount of cargo that can be transported in a certain
period of time [33]. Many researchers argue that more
ships will need to sail to deliver the requested cargo
and, as a result, costs may be even higher as a result of
transporting the total targeted cargo.
3.3 Future Perspectives: Alternative Fuels and Renewable
Energy
The long-term shipping carbon neutralization is not
only possible by improving existing technologies, but
also by adopting low- or zero-carbon alternative
energy sources capable of substituting for fossil fuel.
According to the 2050 net zero vision of IMO, the
sector's reliance on fossil fuels has become a strategic
imperative [12]. Here, renewable energy technologies
and alternative fuels are key for attaining sustainable
shipping.
3.3.1 Alternative Fuels: Hydrogen, Ammonia, Methanol
and Biofuels
As a countermeasure to the high GHG emissions
caused by the use of heavy fuel oil (HFO) containing
high levels of sulphur, there is increasing interest in the
use of liquefied natural gas (LNG), which results in
lower nitrogen oxides (NOX) emissions [34]. Liquefied
natural gas (LNG) reduces CO2 emissions by 20-30%
and minimizes SOX and other emissions [35].
Alternative fuels are fascinating since they are low
in carbon, producible from inexhaustible eco-friendly
sources and carbon neutral. The most studied solutions
today are based on hydrogen, ammonia, methanol and
advanced biofuels.
There are many sources in the literature that
hydrogen can be used effectively in many areas,
especially in the energy, transportation and
construction sectors. Borowski and Karlikowska [36],
who conducted a comprehensive literature review in
this context, stated that hydrogen can be used for
multiple purposes, as it has significant potential in
terms of storage and transfer of renewable energy and
is an important source that can replace fossil fuels.
Hydrogen, which can be used to produce clean
synthetic fuels for maritime transport, will be an
important factor in reducing GHG emissions [37].
Hydrogen fuel is increasingly recognized as a key
alternative for cutting down the carbon emissions in
the maritime sector. When generated from renewable
energy, hydrogen fuel combusts without releasing
carbon, producing only water as a byproduct. It boasts
an energy density roughly three times that of heavy
fuel oil. However, hydrogen brings serious technical
and engineering difficulties in storage due to its
physical properties. Storing hydrogen in gaseous form,
which has a very low density, is not practical because
storing 1 kg of hydrogen in this form would require a
storage volume of approximately 11 m³ [38]. But when
liquidised, it can be stored in 800 times less volume
[39]. However, there are many technical difficulties in
storing it in liquid form. The most significant is that
hydrogen, which liquefies at -253°C (-423°F), would
require multilayer vacuum-insulated tanks to store it at
this temperature. Technical Challenges in Cryogenic
Hydrogen Tank Design are shown in Table 3.
Table 3. Technical Challenges in Cryogenic Hydrogen Tank
Design.
Challenge
Description
Extremely Low
Temperature
Requirement
Liquid hydrogen must be stored at approximately
−253°C (20 K), requiring multi-layer vacuum-
insulated tanks to maintain cryogenic stability
[40].
Heat Ingress and
Boil-off Gas
Formation
Even with advanced insulation, heat ingress leads
to boil-off gas (BOG), increasing internal pressure
that must be actively managed through venting
or reliquefaction systems [40, 41].
Material
Brittleness at
Cryogenic
Temperatures
Conventional structural steels become brittle
under cryogenic conditions; therefore, materials
such as austenitic stainless steels or aluminium
alloys are preferred for hydrogen tanks [42].
Hydrogen
Permeation and
Leakage
Due to its small molecular weight, hydrogen will
diffuse through seals and micro-cracks and may
create leakage, energy loss, and explosive
atmosphere risks when mixed with air [41, 43].
High Energy
Demand for
Liquefaction
Hydrogen liquefaction requires significant energy
input, consuming up to 30% of its usable energy
content, which impacts overall system efficiency
[40, 44].
Safety and
Explosion
Hazard
Hydrogen's flammable range is 4% to 75% in air
and extremely low ignition energy, necessitating
high-tech leak detection, ventilation, and inerting
systems for cryogenic tank design [41, 43].
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These safety issues, in addition to its high retrofit
and operational cost, are barriers it shares with
ammonia [45].
Ammonia, a blend of hydrogen and nitrogen, is a
viable renewable fuel due to its low carbon dioxide
emission, high energy density, and low-cost relative to
other zero-emission fuels. Nevertheless, ammonia as a
ship fuel is risky, mainly owing to its toxicity. Both
crew members onshore and onboard require
appropriate training and equipment, and ships require
construction via stringent safety precautions to lower
leak risk. These factors, coupled with the necessity to
expand green hydrogen production, render ammonia
more expensive than conventional fuels [45].
While geothermal hydrogen and ammonia-
fueled tankers emit about 0.98 g and 1.65 g of CO2
equivalent per tonne-kilometre, respectively,
the conventional heavy fuel oil tanker emits about 5.33
g/tonne-kilometre of CO2 equivalent greenhouse
gases. [46].
Methanol, producible from both renewable
biomass and synthetic processes, offers versatility as a
carbon-neutral fuel option, making it an attractive
choice for maritime transport [35]. There are already
investments in the production of “green” methanol. It
is compatible with current ships since it can be stored
in liquid form. The ability to stock in this way is now
available in the vast majority of the world's largest
ports. Nonetheless, the primary challenge for green
methanol lies in obtaining its components [45].
Research indicates that transitioning the hydrogen
supply to a low-carbon model is significantly more
feasible than doing so for ammonia or methanol. This
is primarily because the processes involved in
producing ammonia and methanol, such as the Haber-
Bosch process and synthesis, are highly energy-
demanding, necessitating a much larger amount of
renewable electricity. Furthermore, hydrogen
production would require the smallest increase in
production capacity to satisfy the global fleet's
demand, with an increase of 171%, compared to 391%
for ammonia and 859% for methanol [47]. 
Biofuels have the potential to decrease life cycle of
GHG emissions if produced from renewable raw
material resources. When produced sustainably,
biofuels can significantly reduce life cycle GHG
emissions, offering a competitive edge over traditional
fuels, provided that the challenges of scalability and
cost-effectiveness are addressed.
The economics of alternative fuel pathways vary
widely․In contrast to the conventional and transitional
fuels which have established supply chains‚ and
bunkering infrastructure‚ the pathways based on
hydrogen‚ ammonia and/or renewable methanol
require investments in the production‚ storage and
bunkering of the alternative fuel and dedicated
systems on board the ship․Biofuels have lower barriers
to use where existing or modified engines can be used‚
but feedstock availability and cost in the long term are
important constraints to take into consideration.
Consequently, the economic feasibility of maritime
decarbonization depends not only on the fuel price
itself but also on infrastructure requirements, vessel
conversion or newbuilding costs, and the availability
of low-carbon fuel production capacity.
However, these benefits should be considered
primarily in the context of short- to medium-term
emission reduction. LNG remains a fossil fuel, and its
long-term contribution to maritime decarbonization is
constrained by the continued dependence on carbon-
based fuel and the potential climate impact of methane
emissions across the fuel supply chain. Therefore, LNG
can provide transitional environmental benefits
compared with conventional marine fuels, but it
should not be regarded as a stand-alone long-term
pathway to achieving the IMO's net-zero objective.
3.3.2 Renewable Energy Sources and Carbon Capture
Photovoltaics (solar panels) may be fitted on a ship
to power auxiliary systems. It helps reduce the use of
fossil fuels when the ship is under slow steaming or in-
port operations.
"M/V Auriga Leader" is among the definition of the
first commercial ship to run on solar power. I was built
to employ 328 solar panels to produce 40kW of
alternative power. But when put on trial it was
understood that power generation problems were
faced and for storage. Aside from such problems,
variability of power supply was felt, due to big panels.
M/V Auriga Leader made its first voyage from Japan to
the US to ship cars [48].
Sails, rotor sails, and kites now make use of wind
energy to move. Wind energy usage reduces main
engine load and fuel. The Wind Challenger project by
MOL and Rotor Sails by Norsepower are two notable
examples when it comes to onboard application of
wind power.
The VLGC Oceanus Aurora has been fitted with a
duo of specially developed Norsepower Rotor Sails
(NPRS). These sails, which stood 20 meters tall and 4
meters wide, are designed to match the air draught
capacity of the ship. The NPRS is a new type of the
Flettner rotor, using minimal electricity to rotate
cylindrical sails on the deck and thereby using wind to
generate massive thrust through the Magnus effect.
This new technology enhances the principal
propulsion system, leading to lower fuel use,
emissions, and fuel expenses [49]. The wind propulsion
system, which is based on artificial intelligence (AI),
employs AI to manage the rotor sail's operation,
including its rotation speed, direction, and rotation,
based on actual weather conditions collected by
sensors. The system therefore optimizes the
performance of the ship with the capability to
minimize fuel consumption and CO₂ emissions. It has
been estimated that wind-assisted propulsion is
capable of saving 12% in fuel use and carbon emissions
annually [50]. Based on the data obtained as a result of
a cumulative 250,000 working hours with this
technology provided by NRS, fuel efficiency savings in
various ships of the shipping sector occurred in 5-25%
[51].
Wind Challenger features two fiberglass-reinforced
plastic telescoping sails that are 49 meters tall at their
highest. The sails are folded back to lower the center of
gravity in the vessel, which enhances stability during
adverse weather conditions. Wind Challenger features
a fully automated control system with patented
technology that relies on sensors to measure wind
speed and direction. This system controls the sails
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automatically by extending them, pulling them in, and
turning them as required. Each 15-meter-width sail is
installed on the 2022-built 100,400-dwt coal carrier
Shofu Maru. During its initial voyage aboard the Wind
Challenger WAP, the Shofu Maru attained a 5%
reduction in fuel consumption on the Japan-Australia
sector and an 8% decrease on the Japan-North America
West Coast sector. When the sails were operated under
automatic control mode, the amount of fuel burned
each day was reduced by up to 17%, as per data
collected from the ship.
In research by Aijjou et al. [52], the most critical
problems concerning the adoption of solar power
onboard a ship were reported as follows:
− The capacity of the ship deck area under sunlight is
restricted by the capacity of the demand of the ship
and cargo.
− The capacity and effectiveness of the solar PV is still
restricted to meet the demand of the ship.
Pesa et al. [53] studied the effectiveness and
limitation of using solar panels and, in parallel with it,
compared it with wind power under the same study.
Considering the time when sunlight is available, they
found that, in 25 years' time, the amount of diesel fuel
to be conserved would be 111,556 liters and 170,274
liters using solar energy and wind energy respectively.
Aijjou et al. [52] also conducted another study on
significant matters of application of solar energy
onboard ships:
− Deck space availability of the ship for sunlight is
restricted due to vessel size.
− Efficiency and capacity of the solar PV system are
low to fulfill the needs of the ship.
Carbon capture and storage (CCS) is a carbon
capture technology that captures carbon gases from
ships prior to emission. It is considered that this
method can be an important tool to reduce carbon
emissions from ships. Although studies on this subject
have been ongoing for a long time, the cost of this
technology is still high [54].
Capture rate is the proportion of CO2 that is
captured relative to the total emissions from the vessel,
factoring in the additional energy and emissions
required to operate the carbon capture system.
Achieving a 100% capture rate with traditional carbon
capture methods may not be feasible; however, net-
zero emissions can be attained by integrating onboard
carbon capture with the use of carbon-neutral fuels.
Several factors constrain the capture rate, including
[55]:
− The technology used for capturing and the space
needed for its onboard application.
− The available space and weight capacity on the
vessel.
− The energy requirements of the technology.
− The power and heat supply resources of the
machinery system, in terms of additional electric
power and thermal supply.
− The type of ship and its trade, particularly the
frequency of port visits.
Using today's technologies, it is possible to prevent
carbon emissions between 40% and 90% with the CCS
system to be established on the ship. It is stated in the
literature that the chemical absorption method, which
requires thermal energy, is the most effective method.
It is predicted that the developing CCS technology will
capture 6% of global CO2 emissions by 2050 [56].
The technologies and alternative fuels described
above vary widely in their potential to reduce
emissions‚ technological maturity‚ requirements for
infrastructure rollout and barriers to implementation․
A summary of the major options considered in this
study is given in Table 4 ․ This comparison is only
qualitative and highlights the various stages of
development of various technologies and the main
conditions for their integration․
Table 4. Comparative assessment of major maritime
decarbonization technologies and fuels.
Technology
/ Fuel
Emission-
reduction
potential
Maturity
(*)
Infrastructure
requirements
Principal
barriers
Energy-
efficiency
measures
Low–high,
depending on
technology
and
application
CM
Limited;
mainly vessel-
specific
Initial
investment;
vessel-specific
applicability
LNG
Lower CO₂
emissions
than fossil
fuels; limited
long-term
decarboniza-
tion potential
CM
Established
but geograp-
hically uneven
bunkering
infrastructure
Fossil-fuel
dependence;
methane
emissions;
infrastructure
lock-in
Biofuels
Potentially
significant,
depending on
feedstock and
production
pathway
CA / ED
Existing fuel
infrastructure
can often be
adapted
Feedstock
availability;
sustainability;
cost
Methanol
Potentially
significant for
low-carbon/
renewable
pathways
ED
Bunkering and
fuel-handling
infrastructure
required
Fuel
availability;
production
cost;
infrastructure
Ammonia
High
potential with
low-carbon
production
D / ED
New storage,
bunkering and
safety
arrangements
Safety;
toxicity; fuel
production;
infrastructure
Hydrogen
Very high
potential with
renewable
production
D / ED
Substantial
new
production,
storage and
bunkering
infrastructure
Storage;
energy
density; cost;
infrastructure
Wind-
assisted
propulsion
Moderate,
depending on
vessel and
route
CA / ED
Limited
additional fuel
infrastructure
Weather/route
dependence;
deck space;
operational
integration
Solar PV
Limited to
moderate as a
supplemen-
tary source
CA
Onboard
installation;
limited
external
infrastructure
Limited power
density;
weather
dependence;
vessel-area
constraints
Onboard
CCS
Potentially
high
D / ED
CO₂ storage,
handling and
port reception
infrastructure
Cost; space;
energy
penalty; CO₂
handling
(*) Explanation of the codes related to Maturity:
CA: Commercially available, CM: Commercially mature,
D: Demonstration, ED: Early deployment.
648
As Table 4 shows‚ the technology readiness and
implementation factors associated with each of these
options are vastly different. Energy efficiency
measures‚ LNG and some renewable-support
technologies are commercially available now‚ while
hydrogen‚ ammonia and onboard carbon capture will
require technological development‚ infrastructure
investment and greater penetration into the market․
Alternative fuels differ in terms of their
decarbonization potential depending on the method of
production․ Therefore‚ maritime decarbonization is
unlikely to be based on one type of technology or fuel
pathway but is likely to consist of a combination of
existing efficiency measures and new and emerging
low-carbon technologies and fuels that gradually
decarbonize the sector․
4 DISCUSSION
Before discussing the implications of the results, it is
important to visualize the systemic tension between
policy ambition and technological feasibility. Figure 2
shows this relationship, demonstrating how regulatory
expectations precede the technological readiness of
decarbonization technologies in the maritime industry.
Figure 2. Relationship between regulatory ambition and
technological readiness in maritime decarbonization.
The bent line (the "Implementation Feasibility
Line") signifies the cutting edge of technological
feasibility; points below the curve correspond to
practically realizable areas, while points above
correspond to the policy target exceeding current
technological maturity.
An analysis of the technology advancements
achieved and available regulation shows that carbon
reduction in shipping is not only a technology
problem; there is an impact on policy and financial
conditions as well. Challenges are evident in a multi-
layered transition process that requires innovation
ecosystems' compatibility with market structures. The
IMO has established various regulations to bring about
the change. Economic conditions, however, complicate
these regulations being implemented in this sector.
Most technical alternatives, such as air lubrication,
hybrid powerplants, alternative fuels, and CCS
technologies, have been found to be applied for
reducing emissions. However, it is a fact that these
methods are not used equally across global fleets.
While more developed fleets and countries with
greater economic power can utilize these methods,
smaller shipowners with less economic power are
lagging behind in adopting these technologies.
The timing of when new fuel technologies will be
available on ships is uncertain. The timing of when this
technology will be feasible is unlikely to align with the
timeframe set for the zero-emission target. Hydrogen
and ammonia appear to be promising alternative
solutions to address the decarbonization goal.
However, there are some serious challenges for these
important alternatives. When we analyse in terms of
hydrogen, it brings serious technical and engineering
difficulties in storage due to its physical properties.
Hydrogen is a combustible gas that diffuses easily,
necessitating specialized crew training and expensive
infrastructure on ships to store it at freezing
temperatures of -253 degrees C (-423 degrees F) by
implementing pressure.
Hydrogen, also appearing to be a principal
alternative, has certain disadvantages such as the cost
of cryogenic cooling, boil-off (boiling/evaporation)
loss, material storage problems, and safety.
Ammonia, being a relatively effective alternate in
terms of energy density, has certain problems owing to
its safety risks. Its highest danger is its toxicity, and it
has been rated by the IMO as a "high consequence toxic
fuel" with the potential of being a life-threatening
hazard to human health. Ammonia is a serious
respiratory irritant that irritates the eyes, throat, and
lungs at concentrations above 50 ppm and is toxic at
concentrations above 2,500 ppm. Apart from human
health hazards, it also poses environmental safety
risks. Thus, employees must be adequately trained and
special security protocols must be cautiously
implemented.
While wind-powered propulsions and solar power
are also considered options, these are determined more
suitable to increase efficiency but cannot serve as total
alternatives to fossil fuels and are determined more
suitable as supporting or hybrid options.
The findings inform us that carbon capture and
storage (CCS) is becoming increasingly relevant as a
bridging option. CCS is considered to be an essential
and workable solution in the period until the use of
entirely new fuels. But the same solution has
disadvantages too. First and foremost, it is an
expensive solution. The solution also requires large
onboard space, so its installation and application may
not be feasible if there are spatial constraints. Another
shortcoming is that if the system is adopted, the system
will require additional manpower. Regulations such as
the CII and EEXI embraced by the IMO provide means
to help measure performance but ignore operators'
behavioral response in depth. Slow steaming, which
can reduce CO₂ emissions, leads to longer transit times
for voyages and a reduction in the amount of cargo
carried. To encourage operators to make this change,
various policies that will reduce costs are needed.
The maritime sector is a sector with many different
actors. If each of them focuses on different objectives, it
will not be possible to achieve perfect results in
decarbonisation. To make emissions reduction efforts
more effective, it would be beneficial to ensure that the
649
levels sacrificed by each player are balanced and
equitable.
5 CONCLUSIONS
In addition to serving as the backbone of global trade,
the maritime sector is also a significant contributor to
global GHG emissions. Producing 2–3% of the world's
greenhouse gas emissions, the sector is hence also a key
player in the battle against climate change [5]. In
pursuit of the vision of the IMO for achieving a net zero
emission by 2050, there is hence an imperative need for
transformation within the sector. This shift must be
supported by technological measures, but also by
broad policies, financial products and multi-actor
coalitions.
This study maps the current status of the maritime
transportation sector regarding carbon emissions,
emerging technologies, standards and transition
strategies in a detailed manner. Examination of the
current status indicates that emission trends by ship
types and operation inefficiencies supplement the
emission burden in the sector. However, measures
articulated by regional and global bodies, especially
IMO, provide important policy directions for reducing
the carbon intensity.
Other fuels (such as methanol, ammonia, hydrogen)
and renewable energy-supported systems (such as
solar cells, sail-assisted propulsion) represents
important options for reducing emissions and
supporting the transition towards zero-emission
shipping. If CCS systems are used in a hybrid model
together with other fuels and/or renewable energy-
supported systems, it will be possible to achieve the
targets depending on the development of technology.
All these systems' elevated costs, scarce
infrastructure possibilities and poorly developed
regulator environment do hinder their spread in the
sector, however. Thereby, economic and operational
issues are the biggest obstacles to the transformation
process. To be more specific, the inability of small and
medium-sized shipowners to pay high investment
costs renders inequality in the transformation process;
and it can clearly be seen that developing countries
need to be assisted further in this process.
Therefore, in the quest to achieve the green
transformation of the maritime industry, apart from
technical solutions, there is a need for full-spectrum
policy alignment, international coordination, equitable
financing models and capacity building initiatives.
For a green maritime future, the adoption in totality
of these proposals will not only bring about
environmental gains but also make world trade more
resilient. The Maritime Sector can be at the forefront of
the green revolution through proper governance and
joint initiatives. Achieving the set goals will be
recorded as an important success in terms of the
maritime sector and maritime management.
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