The Carbon and Shipping Report

Shipping is one of the foundations of global trade, moving raw materials, energy products, manufactured goods and food between markets that may be thousands of miles apart. Its efficiency per unit of cargo is one reason ocean transport carries the majority of internationally traded goods by volume, yet the scale of the system makes its absolute climate footprint strategically important. Carbon performance therefore has to be read in two ways at once: how efficiently ships move cargo and how much total greenhouse gas the maritime system releases.

The emissions profile extends beyond carbon dioxide. International shipping produces CO₂ from fuel combustion, methane from several engine and fuel pathways, nitrous oxide in smaller quantities, and black carbon from incomplete combustion. Those pollutants differ in mass, atmospheric behavior and policy treatment. A fuel switch that lowers direct CO₂ may still require closer scrutiny of methane slip or upstream production, while a conventional oil fuel can remain relevant to black-carbon control even when its CO₂ pathway is already well understood.

Operational conditions add further complexity. Vessel type, speed, engine load, route, cargo utilization, weather, hull condition and time spent waiting at ports all influence fuel use. The same vessel can therefore produce a different carbon result on two voyages of similar distance. Fleet age and fuel compatibility shape what can be changed technically, while port infrastructure determines whether alternative fuels, shore power or more efficient turnaround can be used in practice.

This report follows maritime carbon from the 2012–2017 international-shipping emissions inventory through fuel-specific CO₂, methane, nitrous oxide and black carbon, then widens into efficiency, regulatory targets, EU monitoring, alternative fuels, trade growth and transition readiness. The objective is to separate a shipping pathway that merely improves one metric from one that can deliver verified, system-wide decarbonization while continuing to support global trade.

Executive Carbon and Shipping Benchmarks

The numbers that define maritime emissions

International-shipping CO₂ in the direct inventory moved from 614.1 million tonnes in 2012 to 693.4 million tonnes in 2017. The series was nearly flat between 2012 and 2013, at 614.1 and 612.3 million tonnes, before rising to 634.2 million tonnes in 2014, 657.9 million in 2015 and 675.3 million in 2016. The six-year pattern establishes the central tension in shipping decarbonization: efficiency improvements can occur while absolute emissions still rise when transport work expands.

Fuel structure explains much of that total. Heavy fuel oil contributed 562.9 million tonnes of international-shipping CO₂ in 2017, compared with 130.3 million tonnes from marine diesel oil and about 0.2 million tonnes from natural gas in the same direct series. HFO therefore remained the dominant carbon source in the historical profile, even though MDO's contribution had almost doubled from 66.2 million tonnes in 2012.

Non-CO₂ pollutants are smaller by mass but still important for complete climate accounting. International-shipping methane rose from about 10,157 tonnes in 2012 to 12,397 tonnes in 2017. Nitrous oxide increased from roughly 34,297 tonnes to 39,059 tonnes, while black carbon rose from 54.41 thousand tonnes to 62.17 thousand tonnes. These metrics should remain separate because raw mass does not capture their different climate effects.

The broader headline inventory reinforces the scale. Total shipping greenhouse-gas emissions were 977 million tonnes CO₂e in 2012 and 1,076 million tonnes CO₂e in 2018, an increase of 9.6%. Total-shipping CO₂ increased from 962 million tonnes to 1,056 million tonnes over the same interval, while shipping's share of global anthropogenic emissions moved from 2.76% to 2.89%.

Benchmark area	What it measures	Why it matters
Total CO₂	Absolute carbon output	Core climate outcome
Fuel-specific CO₂	Contribution by fuel	Shows transition exposure
CH₄	Methane emissions	Tests gas-fuel trade-offs
N₂O	Nitrous oxide	Adds non-CO₂ climate impact
Black carbon	Combustion soot	Important short-lived climate pollutant
Carbon intensity	Emissions per transport work	Separates efficiency from growth
International shipping	Cross-border maritime activity	Main global policy focus
Domestic navigation	National shipping activity	Different inventory responsibility

 

Executive readout: Shipping carbon should be evaluated through absolute emissions, fuel mix, non-CO₂ pollutants and transport efficiency together rather than reduced to one headline CO₂ figure.

 

Why Shipping Carbon Requires a System-Based Benchmark

No single emissions number describes the full performance of maritime transport. A vessel may burn less fuel per tonne-mile because it sails more slowly, carries more cargo or uses a more efficient hull, yet the operator may still emit more CO₂ across the year if the ship travels farther or completes more voyages.

Fuel choice adds a second dimension. Combustion CO₂ is easy to compare at the exhaust, but lower tank-to-wake CO₂ does not automatically create the lowest lifecycle climate result. Methane leakage, methane slip, electricity source, hydrogen production method, biofuel feedstock and synthetic-fuel energy requirements can materially change well-to-wake performance.

A credible framework has four layers. The first is absolute emissions, which describes the climate outcome. The second is carbon intensity, which describes operating efficiency. The third is the fuel pathway, including non-CO₂ pollutants and upstream production. The fourth is transition readiness: vessels, ports, contracts, data systems and regulation must all support the pathway.

System readout: Lower carbon intensity does not automatically mean lower total sector emissions when shipping demand and transport work continue to expand.

 

The Historical CO₂ Trajectory of International Shipping

How emissions changed from 2012 to 2017

The international-shipping CO₂ series begins at 614.1 million tonnes in 2012 and slips marginally to 612.3 million tonnes in 2013. That small decline is followed by a sustained rise: 634.2 million tonnes in 2014, 657.9 million in 2015, 675.3 million in 2016 and 693.4 million in 2017. From the 2012 baseline to 2017, the increase is approximately 79.3 million tonnes, or 12.9%.

The shape matters because it prevents a simplistic interpretation of efficiency. A flat or improving vessel-level intensity indicator can coexist with a sector total that is moving upward. More ships, larger cargo flows, longer routes or greater voyage activity can offset gains from speed reduction and larger average ship size.

The later IMO headline inventory shows similar pressure across a broader boundary. Total-shipping CO₂ was 962 million tonnes in 2012 and 1,056 million tonnes in 2018, while total greenhouse gases rose from 977 million tonnes CO₂e to 1,076 million tonnes CO₂e.

Figure 1. International-shipping CO₂ emissions moved upward after 2013, reaching 693.4 million tonnes by 2017.

CO₂ readout: Efficiency gains must be evaluated against demand growth because absolute international-shipping emissions increased across most of the observed period.

 

Heavy Fuel Oil and the Carbon Structure of Shipping

Heavy fuel oil dominates the historical international-shipping CO₂ profile. HFO emissions were 547.8 million tonnes in 2012, 544.6 million in 2013, 532.7 million in 2014 and 523.4 million in 2015. The series then turned upward to 548.3 million tonnes in 2016 and 562.9 million tonnes in 2017. Even at its 2015 low, HFO remained far larger than any other fuel contribution in the direct inventory.

The pattern shows why deep decarbonization requires structural fuel transition. Operational efficiency can reduce the quantity of fuel required to move one unit of cargo, but a system that remains dominated by fossil oil retains a high absolute carbon floor when transport work is large.

HFO also matters beyond CO₂. In the black-carbon series, HFO contributed 45.55 thousand tonnes in 2012 and 47.02 thousand tonnes in 2017. Its share of black carbon remained dominant even when MDO's contribution increased.

Figure 2. Heavy fuel oil remained the dominant international-shipping CO₂ source in 2017, far ahead of MDO and natural gas in the direct inventory.

Fuel readout: The historical carbon profile remains dominated by oil-based fuels, so deep decarbonization requires more than incremental operating improvements.

 

Marine Diesel Oil and the Changing Fuel Mix

Marine diesel oil contributed 66.2 million tonnes of international-shipping CO₂ in 2012 and 67.6 million tonnes in 2013. Its contribution then increased sharply to 101.5 million tonnes in 2014 and 134.4 million tonnes in 2015 before settling at 126.9 million tonnes in 2016 and 130.3 million tonnes in 2017. The 2017 level was almost twice the 2012 value.

That growth does not indicate automatic decarbonization. Changing the mix between oil fuels can alter sulfur, particulate and operating characteristics, yet both HFO and MDO remain carbon-bearing fuels.

The fuel mix also changes non-CO₂ emissions. MDO black carbon rose from 8.86 thousand tonnes in 2012 to 15.15 thousand tonnes in 2017, increasing its contribution to the international total.

Year	HFO CO₂ (Mt)	MDO CO₂ (Mt)	NG CO₂ (Mt)	International total (Mt)
2012	547.8	66.2	0.0	614.1
2013	544.6	67.6	0.0	612.3
2014	532.7	101.5	0.0	634.2
2015	523.4	134.4	0.1	657.9
2016	548.3	126.9	0.1	675.3
2017	562.9	130.3	0.2	693.4

 

Mix readout: The growth of MDO changed the fuel distribution, but total international-shipping CO₂ still increased.

 

Natural Gas, Methane and the Fuel-Switching Trade-Off

Natural gas occupies only a small share of the 2012–2017 direct CO₂ inventory, rising from essentially zero to about 0.2 million tonnes of international-shipping CO₂ by 2017. The historical scale is therefore too small to treat the period as evidence of a mature gas transition.

Methane is the key issue. Gas combustion can reduce direct CO₂ relative to some oil-fuel pathways, but methane slip from engines and leakage across production and distribution can erode the climate benefit. The correct comparison depends on engine technology, fuel supply and the boundary used.

This same principle applies to newer fuels. Ammonia can avoid onboard carbon dioxide but may introduce concerns about nitrous oxide, toxicity and production energy. Hydrogen has no carbon at the point of use but can carry substantial upstream emissions if produced from fossil energy without effective carbon management. Methanol can be fossil, biogenic or synthetic.

Fuel pathway	CO₂ issue	Main non-CO₂ issue	Transition question
HFO	High direct CO₂	Black carbon	How quickly can fossil use fall?
MDO	High direct CO₂	Black carbon / NOx context	Efficiency vs substitution
Natural gas	Potentially lower direct CO₂	Methane slip	Does methane erase benefit?
Low/zero-carbon fuels	Pathway dependent	Varies by fuel	What is the lifecycle footprint?

 

Gas readout: A lower direct CO₂ profile is not a complete climate result when methane emissions and upstream fuel production are excluded.

 

Methane Emissions from Shipping

Why CO₂ does not tell the whole climate story

International-shipping methane was about 10,157 tonnes in 2012 and remained close to that level in 2013 before moving upward to 10,415 tonnes in 2014. The series then increased to approximately 11,206 tonnes in 2015, 11,745 tonnes in 2016 and 12,397 tonnes in 2017. That is a rise of roughly 22% from 2012 to 2017.

Methane's mass is tiny beside hundreds of millions of tonnes of CO₂, but raw tonnes are not the correct way to compare climate importance across gases. Methane has a much stronger warming effect per unit over relevant time horizons, which is why the gas becomes especially important when evaluating LNG and other methane-based fuel pathways.

The commercial implication is stronger measurement. A vessel operator that claims lower carbon because direct CO₂ falls should also know how much methane is released by the engine and how the fuel was produced.

Figure 3. Methane and nitrous oxide both increased over the 2012–2017 international-shipping series; the chart indexes each pollutant to its own 2012 baseline.

Methane readout: Fuel pathways that increase gaseous-fuel use should be judged on total greenhouse impact rather than direct CO₂ alone.

 

Nitrous Oxide and Smaller Pollutants That Still Matter

International-shipping nitrous oxide rose from about 34,297 tonnes in 2012 to 39,059 tonnes in 2017. The intermediate values were approximately 34,270 tonnes in 2013, 35,568 in 2014, 36,942 in 2015 and 37,958 in 2016.

The total-shipping inventory, including domestic navigation and fishing, is larger than the international-only series. This difference is another reason inventory boundaries should remain visible.

N₂O also becomes more important in future-fuel discussion because some combustion pathways can affect its formation. A low-carbon fuel should therefore be evaluated across all material greenhouse gases rather than awarded a premium score based only on the absence of carbon in the fuel molecule.

N₂O readout: Climate accounting should preserve pollutant-specific units and boundaries instead of comparing raw tonnes as if every greenhouse gas were equivalent.

 

Black Carbon from International Shipping

Short-lived climate forcing beyond greenhouse gases

International-shipping black carbon increased from 54.41 thousand tonnes in 2012 to 62.17 thousand tonnes in 2017. The series rose to 55.76 thousand tonnes in 2013 and 60.06 thousand tonnes in 2014, eased slightly to 59.90 thousand tonnes in 2015, and then increased again to 60.67 thousand tonnes in 2016.

HFO remained the largest contributor throughout the period, moving from 45.55 thousand tonnes to 47.02 thousand tonnes. MDO increased more sharply, from 8.86 thousand tonnes to 15.15 thousand tonnes. Natural-gas black carbon was negligible in the direct dataset.

Black carbon differs from CO₂ because it is a short-lived climate pollutant with strong regional relevance, particularly where deposition can affect snow and ice. A comprehensive maritime strategy should therefore preserve pollutant-specific controls rather than assuming that a CO₂ pathway automatically solves all climate-forcing emissions.

Figure 4. International-shipping black carbon increased from 54.41 thousand tonnes in 2012 to 62.17 thousand tonnes in 2017.

Black-carbon readout: Maritime climate strategy should distinguish long-lived CO₂ from shorter-lived pollutants whose geography and atmospheric effects differ.

 

International Shipping Versus Domestic Navigation

Inventory boundaries materially change the picture. International-shipping CO₂ was 614.1 million tonnes in 2012 and 693.4 million tonnes in 2017. Domestic navigation was much smaller but still significant, increasing from 142.2 million tonnes to 155.5 million tonnes over the same period. Fishing contributed a further 20.7 million tonnes in 2012 and 18.8 million tonnes in 2017.

When those components are combined, total shipping CO₂ rises from 777.0 million tonnes in 2012 to 867.6 million tonnes in 2017. The total is useful for understanding the complete maritime footprint, but international shipping is usually the central focus of global IMO policy because emissions occur across jurisdictions and cannot be managed by one national government alone.

Domestic navigation sits inside national or regional policy systems and may have different vessel types, route lengths and opportunities for electrification or shore power. Short-sea ferries, inland navigation and local service vessels can therefore follow different technology pathways from deep-sea container ships or bulk carriers.

Dimension	International shipping	Domestic navigation
Activity boundary	Cross-border maritime transport	Within national inventory boundaries
Policy scale	International coordination	National / regional
2017 CO₂	693.4 Mt	155.5 Mt
Transition challenge	Global fuel and fleet coordination	Local infrastructure and policy
Best use of data	Global sector strategy	National implementation

 

Boundary readout: International and domestic navigation should remain separate because their inventory rules, policy responsibilities and vessel mixes differ.

 

Carbon Intensity Versus Absolute Emissions

Absolute emissions answer how much carbon shipping releases. Carbon intensity asks how much carbon is released for a unit of transport work. The distinction matters because a sector can become more efficient while still emitting more in total. In the IMO headline data, AER carbon intensity improved by about 21% relative to 2008 by 2018, while EEOI improved by about 29%. Yet total-shipping CO₂ was higher in 2018 than in 2012.

The IEA efficiency context reinforces the same point. Shipping activity expanded by about 50% from 2008 to 2023 while energy use rose only around 5%. Energy intensity improved by about 30%, indicating that the sector carried much more activity for only a modest increase in energy consumption. Those gains are substantial, but annual CO₂ remained close to 700 million tonnes in the IEA sector estimate.

The appropriate benchmark therefore needs two scorecards. The first measures intensity improvement and rewards operational efficiency.

Figure 5. Shipping activity and average ship size increased strongly since 2008 while energy use grew much more slowly, average speed fell and energy intensity improved.

Intensity readout: Carbon intensity measures efficiency; absolute emissions measure climate outcome. A credible shipping strategy needs both.

 

Vessel Efficiency and Operational Carbon Reduction

Operational efficiency is the fastest lever available to much of the existing fleet. Slow steaming can reduce engine power demand, while weather routing can avoid conditions that increase resistance and fuel burn.

The IEA attributes about two-thirds of historical efficiency gains to slow steaming and reports an average speed reduction of roughly 10% since 2008. Average ship size increased by about 50% over the same period, allowing more cargo to be moved per voyage when capacity is well utilized. Combined improvements saved an estimated 1.8 million barrels of oil per day and about USD 60 billion in fuel costs in the 2023 efficiency assessment.

Those gains illustrate the economic case for efficiency, but operational measures have limits. A vessel that remains dependent on fossil fuel will continue to emit carbon even when it is operated well.

Operational lever	Carbon mechanism	Main trade-off
Slow steaming	Lower engine power and fuel burn	Longer transit time
Weather routing	Avoids high-resistance conditions	Routing flexibility
Hull / propeller maintenance	Reduces drag	Maintenance downtime
Trim optimization	Improves hydrodynamics	Monitoring requirement
Port-call efficiency	Cuts waiting and idling	Port coordination
Cargo utilization	More work per voyage	Demand dependent

 

Efficiency readout: Operational efficiency can reduce emissions immediately, but it cannot alone deliver deep decarbonization if the fleet remains dependent on carbon-intensive fuels.

 

Ship Energy-Efficiency Regulation

Maritime carbon regulation increasingly connects vessel design with operating performance. Design-oriented standards influence the efficiency of new ships, while operational carbon-intensity requirements push existing vessels to measure annual performance and improve when results fall outside the required trajectory.

Measurement sits at the center of that framework. Fuel consumption, distance, cargo capacity and voyage activity need to be reported consistently before operators can compare vessels or verify improvement.

The next step is integration with fuel carbon intensity. A ship that is technically efficient but consumes a high-carbon fuel may still face a poor long-term climate pathway. Conversely, a low-carbon fuel can be wasted on an inefficient hull or route.

Regulatory readout: Maritime carbon regulation is moving from design efficiency toward operational performance and lifecycle fuel choice.

 

IMO Decarbonization Direction

The 2023 IMO strategy establishes a staged direction for international shipping. By 2030, the sector is targeted to reduce CO₂ intensity by at least 40% relative to 2008. The strategy also calls for zero- or near-zero greenhouse-gas fuels, technologies and energy sources to represent at least 5% of shipping energy by 2030, while striving for 10%.

For annual greenhouse-gas emissions, the strategy includes a 2030 checkpoint of at least 20% reduction relative to 2008 while striving for 30%. By 2040, the corresponding checkpoints rise to at least 70% and a striving level of 80%. The direction is toward net-zero greenhouse-gas emissions from international shipping by or around 2050, taking national circumstances into account.

The transition implied by those checkpoints is much larger than an efficiency program alone. IMO analysis cited in the workbook associates about 64% of the required 2050 CO₂ reduction with alternative low- and zero-carbon fuels.

Policy readout: The regulatory pathway increasingly requires simultaneous improvement in vessel efficiency, fuel carbon intensity and energy-system supply.

 

EU Maritime Carbon Regulation and MRV

European monitoring gives a more recent view of fleet-level carbon. In 2024, the EU MRV system recorded about 144.9 million tonnes of CO₂ from approximately 12,700 reporting ships on EEA-linked voyages. Reported CO₂ increased 12.9% from 2023, while distance travelled rose 9.3% and time at sea increased 8.6%.

The 2024 system also quantified non-CO₂ greenhouse gases at about 3.7 million tonnes CO₂e, including roughly 2.2 million tonnes CO₂e of nitrous oxide and 1.6 million tonnes CO₂e of methane. These values demonstrate the practical shift from CO₂-only reporting toward broader greenhouse-gas accounting.

Container ships were a major driver of the year-on-year change. Their emissions increased 46%, adding about 16.7 million tonnes of CO₂. This is commercially important because it ties emissions directly to the volume and operating pattern of one of global trade's most visible vessel segments.

 

EU readout: Carbon reporting converts fuel consumption from a technical operating variable into a regulatory and financial performance metric.

 

Alternative Marine Fuels and Carbon Pathways

Alternative fuels differ more in production pathway than their labels suggest. LNG or natural gas can reduce direct CO₂ relative to some oil fuels but must control methane slip and upstream leakage. Biofuels can offer drop-in compatibility in some applications, yet their climate value depends on feedstock, land-use effects, processing energy and certification.

Ammonia removes carbon from the molecule used onboard, which makes it attractive for deep decarbonization, but the production pathway determines whether the fuel is genuinely low-carbon. It also introduces safety and emissions-management requirements, including the need to control nitrous oxide or ammonia slip.

The strategic comparison should therefore include six dimensions: direct CO₂, non-CO₂ emissions, lifecycle production, onboard safety, infrastructure and scale. Fuel cost belongs beside those metrics because a technically low-carbon fuel cannot decarbonize a global fleet until it is available in sufficient volume and can be purchased under commercially viable contracts.

Fuel pathway	Direct CO₂	Main non-CO₂ issue	Infrastructure challenge	Transition role
LNG / NG	Lower than oil in combustion	Methane	Bunkering + methane control	Pathway dependent
Biofuels	Accounting depends on pathway	Feedstock effects	Sustainable supply	Near-term / drop-in
Methanol	Source dependent	Production pathway	Tank volume + supply	Growing option
Ammonia	No onboard carbon	N₂O / toxicity	Production + bunkering	Long-term candidate
Hydrogen	No onboard carbon	Production pathway	Storage + bunkering	Niche / long-term
Electricity	No onboard combustion	Grid carbon	Charging + range	Short-sea potential

 

Fuel-transition readout: The lowest-carbon shipping fuel is determined by its complete production and use pathway, not just whether the molecule contains carbon.

 

Fleet Renewal and the Decarbonization Timing Problem

Ships are long-lived capital assets, which turns decarbonization into a timing problem. Owners ordering vessels today have to make assumptions about fuels, engines, bunkering networks and regulation that may evolve over decades.

The existing fleet faces a different decision. Many ships can improve through operational measures, hull retrofits, propulsion upgrades or engine modifications, but not every vessel can economically adopt every future fuel.

This uncertainty increases the value of fuel-ready designs and modular transition planning. A vessel does not need to predict the future perfectly, but the investment case should identify what would be required to switch fuels, how much tank capacity changes, what port network is needed and whether the asset remains compliant under more demanding carbon-intensity trajectories.

Fleet readout: Shipping decarbonization is partly a timing problem because fuel infrastructure, new vessels and retrofit cycles must align over decades.

 

Ports, Bunkering and Carbon Infrastructure

Ships cannot transition faster than the energy system that serves them. Alternative-fuel bunkering requires production, transport, storage, safety procedures and trained personnel at ports. Shore power needs grid capacity, compatible vessel connections and enough time alongside to create a meaningful benefit.

Large ports create a particular opportunity because infrastructure can influence many ship calls. A new fuel terminal, shore-power connection or green-corridor agreement can support multiple carriers rather than one vessel.

Port readiness should therefore be scored separately from vessel readiness. A dual-fuel ship with no reliable bunkering network is not fully transition-ready, while a port with alternative fuels but few compatible vessels cannot use its infrastructure efficiently. Decarbonization depends on both sides of the interface moving together.

Port readout: Vessel technology cannot decarbonize shipping alone; fuel and electricity infrastructure at ports must change at the same pace.

 

The Commercial Value of Lower-Carbon Shipping

Carbon performance is increasingly part of voyage economics. Fuel has always been one of shipping's largest variable costs, and efficiency therefore creates an immediate financial benefit. The IEA estimate of about USD 60 billion in fuel-cost savings from accumulated efficiency gains shows how closely emissions and operating economics can align.

Regulation adds a second value layer. Verified emissions can influence compliance cost, chartering decisions, financing, cargo-owner reporting and the perceived transition risk of a vessel. An older ship with poor intensity performance may remain technically capable of transporting cargo but become commercially disadvantaged if carbon cost or customer requirements rise faster than its ability to improve.

Cargo owners also influence the market. Companies seeking lower supply-chain emissions can specify transport emissions, purchase green-fuel services or favor carriers able to provide verified data.

Commercial readout: Carbon performance is moving from an environmental disclosure issue toward a direct operating, financing and contracting variable.

 

Global Maritime Trade and Carbon Context

The scale of maritime trade explains why shipping emissions cannot be reduced to a small transport niche. More than 80% of goods traded internationally are moved by sea in the UNCTAD context used for this report. Seaborne trade grew about 2.2% in 2024, while ton-mile demand increased 5.9%, indicating that distance can grow faster than physical cargo volume when routes lengthen or trade patterns change.

The near-term outlook remains uncertain. UNCTAD's 2025 forecast in the dataset points to only about 0.5% seaborne-trade growth for the year, but average annual growth through 2030 is projected around 2%.

This reinforces the need to evaluate emissions against transport demand. If trade expands 2% per year, carbon intensity has to improve faster than that just to keep absolute emissions from rising, before accounting for route changes or shifts in cargo mix.

Trade readout: Shipping carbon is inseparable from transport demand because efficiency improvements must outrun growth in maritime trade to reduce absolute emissions.

 

Regional Shipping Carbon Signals

Europe combines stringent carbon reporting with some of the world's largest container, ferry and bulk-shipping markets. The EU MRV framework gives regulators and operators a detailed view of emissions on EEA-linked voyages, while major ports can become early hubs for shore power, methanol, ammonia or other alternative fuels.

Asia combines shipbuilding scale, manufacturing exports and some of the world's busiest maritime hubs. China, Japan and South Korea can influence fleet decarbonization through vessel design and equipment supply, while Singapore's bunkering role gives it leverage over the availability of new marine fuels.

North America has a different mix of long coastlines, major container gateways, energy exports and domestic shipping. Port-air-quality programs and cargo-owner pressure can accelerate local improvements, while deep-sea trade still depends on international standards.

Regional readout: Geography changes the decarbonization problem because fuel supply, cargo mix, fleet type, ports and regulatory pressure vary substantially between regions.

 

Country-Level Maritime and Carbon Signals

Country-level maritime analysis is most useful when it describes roles rather than pretending that one national statistic determines fleet carbon quality. China combines large trade flows, major ports and shipbuilding capacity, giving it leverage over both transport demand and the technology entering the global fleet.

Singapore's role is different. As a major bunkering and transshipment hub, its transition leverage comes from fuel availability, standards and the ability to aggregate demand from many carriers.

The United States is a major cargo market with a distributed port system and significant domestic and international shipping activity. The UAE and other Gulf states combine bunkering with energy production, creating potential to supply lower-carbon hydrogen-derived fuels if lifecycle emissions and certification meet international requirements. Country scale therefore identifies where investment can have leverage, but actual carbon performance still needs vessel- and voyage-level evidence.

Country / hub	Primary maritime role	Carbon opportunity	Main watch point
China	Trade + shipbuilding	Scale efficient and future-fuel vessels	Absolute activity scale
Singapore	Bunkering + transshipment	Alternative-fuel hub	Fuel supply transition
United States	Major cargo market	Port and fleet efficiency	Distributed regulation
Japan	Shipping + shipbuilding	Technology deployment	Fleet transition timing
South Korea	Shipbuilding	Future-fuel newbuilds	Fuel uncertainty
Netherlands	Port / logistics gateway	Port decarbonization	Infrastructure scale-up
Germany	European shipping market	Regulatory alignment	Cost transition
UAE	Energy + bunkering	Low-carbon fuel production	Lifecycle certification

 

Country readout: National maritime scale identifies where decarbonization investment can have leverage, but it does not by itself indicate lower fleet carbon intensity.

 

Major Shipping Hubs and Carbon Leverage

High-traffic shipping hubs concentrate both emissions and opportunity. A large transshipment or bunkering port may handle thousands of vessel calls, which means one infrastructure change can influence many fleets.

Green corridors build on the same principle. Instead of waiting for every port and route to become ready at once, carriers, cargo owners, fuel suppliers and governments can coordinate investment around selected trades. Concentrated demand can support fuel-production contracts and reduce the risk that expensive bunkering infrastructure remains underused.

The challenge is interoperability. Ships trade internationally and may call at several hubs on one service. Fuel specifications, safety procedures, carbon certification and reporting formats therefore need enough consistency that a vessel can operate across regions without carrying a different compliance system for every port.

Hub readout: High-traffic maritime hubs can accelerate decarbonization because infrastructure, fuel supply and reporting systems can scale across many operators.

 

Building the Carbon and Shipping Benchmark Index

The Carbon and Shipping Benchmark Index converts the report into eight weighted pillars. Absolute CO₂ reduction receives 18%, the largest weight, because the final climate outcome must decline rather than only become more efficient. Carbon-intensity improvement receives 17%, ensuring that operators are rewarded for moving cargo with less fuel and fewer emissions per unit of transport work.

Fuel carbon pathway receives 15% because the energy source determines the long-term floor for emissions. Methane and non-CO₂ control receive 12%, preventing a lower-CO₂ pathway from masking methane slip, nitrous oxide or black carbon. Operational efficiency receives 11%, fleet and technology readiness 10%, port and infrastructure readiness 9%, and disclosure and verification 8%.

Scores from 0 to 39 indicate carbon-intensive or poorly verified performance. A score of 40 to 59 represents a transitional pathway, 60 to 74 improving performance, 75 to 89 advanced low-carbon performance, and 90 to 100 exceptional decarbonization readiness. Sub-scores should remain visible because a strong result in one pillar should not conceal weakness elsewhere.

Figure 6. The benchmark gives the largest weights to absolute CO₂ and carbon intensity while preserving separate scores for fuel pathway, non-CO₂ pollutants and infrastructure readiness.

Index readout: A high-performing shipping pathway must reduce absolute emissions as well as improve intensity; efficiency alone should not earn a premium score if total carbon output remains high.

 

Shipping Decarbonization Challenges

Demand growth is the first challenge. Shipping activity expanded about 50% from 2008 to 2023 in the IEA context while energy use increased only 5%, demonstrating major efficiency improvement. Yet the climate target is not to hold energy use nearly flat while trade expands indefinitely; absolute greenhouse-gas emissions must move decisively downward.

Fuel uncertainty is the second challenge. Owners must order long-lived vessels while the future balance between methanol, ammonia, LNG-derived pathways, biofuels, hydrogen and other options is still developing. Infrastructure providers face the mirror problem: building a terminal requires enough demand to justify investment, but owners hesitate to order compatible ships until fuel supply is reliable.

Measurement boundaries form the third challenge. International, domestic and total-shipping inventories answer different questions. Tank-to-wake and well-to-wake emissions are not interchangeable. CO₂, CO₂e, methane, nitrous oxide and black carbon cannot be combined casually. Good reporting preserves the method, year, scope and unit so users know exactly what improved.

Cost is the final major constraint. Alternative fuels can carry significant premiums, and new infrastructure requires capital before utilization is certain. Efficiency, financing, carbon pricing and long-term offtake contracts will therefore shape how quickly technically feasible pathways become commercially scalable.

Challenge readout: Shipping decarbonization is difficult because emissions, fleet investment, global trade growth and fuel infrastructure must change together rather than sequentially.

 

90-Day Carbon and Shipping Benchmark Plan

Days 1 to 30 should establish the baseline. Record vessel type, deadweight, fuel type, fuel consumption, distance, cargo carried, voyage duration, time at sea, port waiting and all available CO₂, methane and nitrous-oxide data. Separate laden and ballast legs where practical and identify whether the voyage belongs to international or domestic accounting. Calculate at least one consistent carbon-intensity indicator.

Days 31 to 60 should test operational improvement. Compare controlled speed changes, route optimization, hull and propeller condition, trim, engine settings, cargo utilization and port-arrival timing. Record not only fuel saved but any service or schedule trade-off. The purpose is to identify measures that remain commercially sustainable rather than one-off laboratory-style reductions.

Days 61 to 90 should add fuel and compliance scenarios. Compare the existing vessel with retrofit, lower-carbon fuel and replacement options. Include fuel availability, expected carbon-intensity trajectory, methane or other non-CO₂ exposure, carbon cost and the ports needed to support each pathway. The output should be a decision matrix that separates immediate operational gains from capital-intensive transition choices.

90-day readout: The objective is not simply to identify the lowest-fuel voyage; it is to identify the operating and fuel pathway that reduces verified carbon without shifting emissions into another part of the lifecycle.

 

Metrics Shipping Companies and Cargo Owners Should Track

Emissions metrics should begin with total CO₂ and preserve separate CH₄, N₂O and black-carbon values where available. CO₂e can be useful for consolidated climate reporting, but the underlying gases should remain visible so operators can identify whether a fuel change creates a new problem. Carbon intensity then connects those emissions with transport work.

Operational metrics include fuel per nautical mile, fuel per tonne-mile, average speed, engine load, ballast distance, cargo utilization, port waiting and time at sea. Fleet metrics include vessel age, design efficiency, retrofit status and fuel compatibility. These measures explain why two ships carrying similar cargo can produce different emissions outcomes.

Commercial metrics should add fuel cost, carbon cost, charter performance, cargo-owner reporting and the cost of transition investment. Verification matters across every family: audited or independently checked data has more strategic value than an unverified estimate when a company is making fleet or fuel decisions.

Metric family	Core measurement	Strong performance signal
Absolute carbon	Tonnes CO₂	Declining total
Intensity	CO₂ per transport work	Declining intensity
Methane	CH₄ / CO₂e	Controlled slip and leakage
Fuel efficiency	Fuel per distance / work	Lower consumption
Port efficiency	Waiting / idle time	Reduced idle exposure
Fleet readiness	Fuel / retrofit compatibility	Transition flexibility
Verification	Reported and checked data	High confidence
Commercial	Carbon-adjusted voyage cost	Competitive low-carbon operation

 

Scorecard readout: Fuel consumption measures cost, but absolute emissions, transport intensity and lifecycle fuel carbon determine whether shipping performance is actually improving.

 

How Carbon Performance Changes by Business Model

Shipowners control the long-lived asset. Their decisions determine hull efficiency, engine type, fuel compatibility and retrofit potential. Operators control how the vessel is used from voyage to voyage, including speed, route, engine settings and maintenance. A highly efficient new ship can still underperform if operations are poor, while an older ship can improve materially through disciplined management even if its technical ceiling remains lower.

Charterers and cargo owners influence demand. Speed instructions, route choices, contract structures and willingness to pay for lower-carbon fuel can determine whether an operator has the commercial flexibility to reduce emissions. Cargo owners also decide whether verified shipping emissions become part of procurement and supply-chain accounting.

Ports and fuel suppliers shape the energy environment, while financiers influence which vessels and technologies receive capital. The transition is shared across the value chain. A credible decarbonization strategy assigns each actor the metrics it can control rather than placing the entire burden on the vessel owner.

Business-model readout: Shipping emissions are shared across the value chain because owners control assets, operators control voyages, ports control infrastructure and cargo owners influence demand for lower-carbon transport.

 

The Carbon and Shipping Report FAQ

How much CO₂ did international shipping emit in 2017?

The direct international-shipping inventory records 693.4 million tonnes of CO₂ in 2017. That figure covers international shipping within the stated inventory boundary and should not be substituted for total-shipping or voyage-based figures that use different scopes.

Did shipping CO₂ increase between 2012 and 2017?

Yes. International-shipping CO₂ increased from 614.1 million tonnes in 2012 to 693.4 million tonnes in 2017, a rise of about 79.3 million tonnes or 12.9%. The increase occurred even though vessel efficiency improved across the broader period.

Which fuel contributed the most CO₂?

Heavy fuel oil dominated the historical direct series. In 2017, HFO contributed 562.9 million tonnes of international-shipping CO₂, compared with 130.3 million tonnes from MDO and about 0.2 million tonnes from natural gas.

Is LNG automatically a low-carbon shipping fuel?

No. Direct combustion CO₂ can be lower than some oil-fuel pathways, but methane slip and upstream leakage can materially change the lifecycle result. The engine, supply chain and accounting boundary all matter.

What is black carbon?

Black carbon is a soot-like product of incomplete combustion and a short-lived climate pollutant. International shipping emitted about 62.17 thousand tonnes in 2017 in the direct series, with HFO providing the largest share.

Is carbon intensity the same as total emissions?

No. Carbon intensity measures emissions relative to transport work, while absolute emissions measure the total climate output. Intensity can improve while total emissions rise if shipping activity grows faster than efficiency.

Why separate international and domestic shipping?

They belong to different inventory and policy boundaries. International shipping requires global coordination across routes and jurisdictions, while domestic navigation can often be addressed through national or regional policy and infrastructure.

Can operational efficiency decarbonize shipping by itself?

Operational efficiency is essential but insufficient for deep decarbonization. Slow steaming, route optimization and maintenance can reduce energy demand, yet a fleet that remains dependent on fossil fuels retains a substantial carbon floor.

What matters most when comparing alternative fuels?

The comparison should cover direct CO₂, methane and other non-CO₂ emissions, lifecycle production, safety, infrastructure, vessel compatibility, fuel availability and cost. Fuel labels alone do not define climate performance.

What should companies track?

Companies should at minimum track total CO₂, carbon intensity, fuel consumption, cargo work, methane where relevant, port waiting, vessel efficiency and verified reporting. Commercial tracking should add fuel and carbon costs.

Final Takeaway

Shipping carbon should be judged by verified system performance rather than a single efficiency claim. International-shipping CO₂ increased from 614.1 million tonnes in 2012 to 693.4 million tonnes in 2017, even as efficiency improved across the broader period. The historical outcome shows why carbon intensity and absolute emissions need to be tracked in parallel.

Fuel structure remains decisive. HFO contributed 562.9 million tonnes of international-shipping CO₂ in 2017 and MDO another 130.3 million tonnes, while natural gas remained small in that historical inventory. Deep decarbonization therefore requires a major change in the carbon content of marine energy as well as continued reductions in fuel demand.

Non-CO₂ pollutants further complicate the transition. International-shipping black carbon reached 62.17 thousand tonnes in 2017, methane was about 12,397 tonnes and nitrous oxide about 39,059 tonnes. EU MRV data for 2024 further demonstrates that methane and nitrous oxide now matter directly to modern fleet reporting, not only to academic inventory work.

Premium maritime carbon performance is verified system decarbonization. The strongest pathway reduces absolute CO₂, improves transport efficiency, controls methane and other pollutants, transitions fuel supply, prepares vessels and ports for new energy, and preserves transparent data boundaries. That balance is more useful than any single headline metric because it reflects the real challenge: carrying the world's trade with progressively less climate impact.