Decarbonising dry bulk shipping means cutting the greenhouse gas emissions produced when bulk carriers burn fuel to move cargo such as coal and iron ore. It combines a regulatory framework set by the International Maritime Organization with practical levers: running ships more efficiently and, over time, switching to lower-carbon fuels.
What does decarbonising dry bulk shipping mean?
Decarbonising dry bulk shipping means reducing the carbon dioxide and other greenhouse gases released when a bulk carrier consumes marine fuel on a voyage. Almost all of those emissions come from burning fuel oil in the main engine and generators, so cutting emissions comes down to burning less fuel, or burning fuel that carries less carbon.
The subject has two distinct halves that are easy to confuse. The first is the regulatory framework, which sets out what owners are required to measure and report. The second is the set of physical and operational changes that actually lower fuel burn, from how fast a ship sails to what it burns. This page describes both structurally rather than tracking any particular year’s market or policy moves.
A common point of confusion is treating decarbonisation as a single switch to a “green fuel”. In practice it is a layered process. Efficiency measures apply to the existing fleet today and reduce emissions whatever the fuel, while alternative fuels are a longer transition constrained by ship design, fuel availability, and cost. Both happen at once, and the regulatory framework is what ties them together.
The IMO regulatory framework
The International Maritime Organization (IMO), the United Nations agency that regulates international shipping, sets the global framework for ship emissions. The relevant rules sit within MARPOL Annex VI, the convention chapter that governs air pollution from ships, and they are reinforced by the IMO’s overarching greenhouse gas strategy.
The 2023 IMO GHG Strategy is the policy umbrella. It sets out the IMO’s stated ambition to reduce greenhouse gas emissions from international shipping, with checkpoints over the coming decades. Beneath that strategy, two technical measures apply directly to individual ships, and it helps to keep them apart because they work in different ways:
- EEXI (Energy Efficiency Existing Ship Index). A technical measure. It rates a ship’s design efficiency, broadly the carbon emitted per unit of transport work given the ship’s engine power, size, and hull. A vessel must meet a required index value. It is assessed against the ship as built and modified, not against how the ship is actually operated on a given voyage. Owners who fall short often respond with engine power limitation or efficiency retrofits.
- CII (Carbon Intensity Indicator). An operational measure. It scores how efficiently a ship is run in service, based on the fuel it actually consumes relative to the distance it sails and its capacity. Each ship receives an annual rating on a banded scale, and a ship that rates poorly is expected to follow a corrective plan. Because CII depends on real operations, it is influenced by speed, routing, port waiting time, and how fully the ship is loaded.
The contrast is the useful part. EEXI asks whether the ship is built efficiently and is a one-time hurdle tied to design. CII asks whether the ship is run efficiently and is an ongoing annual measure tied to operations. A vessel can clear its EEXI design rating and still earn a weak CII band if it spends a lot of time steaming fast or sitting idle with engines running. Attribution for both measures is the IMO under MARPOL Annex VI.
A frequent misunderstanding is to read EEXI and CII as the same requirement expressed twice. They are complementary: one constrains the hardware, the other constrains the behaviour, and a ship has to attend to both.
Efficiency levers on existing ships
Efficiency is where most near-term emissions reduction sits, because it applies to the fleet already trading without waiting for new fuels or new ships. The main levers fall into operational and technical groups.
- Slow steaming. Reducing speed cuts fuel consumption sharply, because a ship’s fuel burn rises steeply with speed. Sailing slower is the single most direct way to lower emissions per voyage, and it feeds straight into a better CII score. The trade-off is voyage time, which is a commercial decision shared between owner and charterer and reflected in the time charter terms.
- Voyage and weather routing. Planning a route to avoid adverse currents and heavy weather, and trimming the ship for optimal draught, reduces resistance and fuel burn. Better arrival planning that avoids steaming fast only to wait at anchor also helps, which connects to how a voyage estimate is built.
- Hull and propeller condition. Marine growth on the hull increases drag. Regular hull cleaning, high-performance antifouling coatings, and propeller polishing keep resistance low and consumption down over the docking cycle.
- Hull and propulsion design improvements. On the technical side, energy-saving devices such as improved bow forms, propeller ducts, and flow-optimising appendages reduce the power needed for a given speed. Larger, slower-turning propellers and optimised hull lines on newbuildings push design efficiency further.
- Engine and machinery measures. Engine power limitation, waste-heat recovery, and tighter management of auxiliary load reduce fuel use and help a ship meet its EEXI requirement.
- Wind-assist and shore power. Auxiliary wind propulsion such as rotor sails or rigid wing sails can supplement the main engine on suitable routes, and using shore power in port avoids running generators at the berth.
These levers stack. None of them depends on a new fuel, and most improve the economics of a voyage at the same time as the emissions profile, because bunker fuel is one of the largest costs in chartering a bulk carrier.
Alternative fuels and their trade-offs
Alternative fuels are fuels that carry less carbon than conventional heavy fuel oil, or none at the point of use. They are the longer arm of decarbonisation because they require compatible engines, onboard storage, and a supply chain at the right ports, so the fleet transitions gradually rather than all at once. No single fuel is a clear winner; each carries a different mix of emissions benefit, cost, availability, and handling difficulty.
The table below contrasts the main options at a structural level. It describes the nature of each trade-off rather than quoting prices or emission percentages, which vary by production pathway and over time.
| Fuel option | Emissions benefit | Main trade-offs |
|---|---|---|
| Conventional very low sulphur fuel oil (VLSFO) | Baseline; meets sulphur limits but no carbon reduction | Widely available and lowest-friction, but does not address greenhouse gas emissions |
| LNG (liquefied natural gas) | Lower carbon dioxide at the engine than fuel oil | Needs cryogenic storage and dual-fuel engines; methane slip can offset part of the benefit |
| Methanol | Lower carbon at use, and very low when produced from renewable sources | Lower energy density needs more tank volume; toxicity and bunkering infrastructure are constraints |
| Ammonia | No carbon dioxide at the point of combustion | Toxic and corrosive, demanding strict safety handling; engines and supply are still maturing |
| Biofuels | Reduced lifecycle carbon, often usable as a drop-in blend | Feedstock availability and sustainability vary; supply can be limited and priced at a premium |
Two themes run through the comparison. First, the benefit of any fuel depends heavily on how it is produced, since a fuel made with fossil energy delivers far less lifecycle saving than the same fuel made with renewable energy. Second, the more carbon a fuel removes, the more it tends to demand in ship design, safety handling, and infrastructure. That is why efficiency measures and fuel switching proceed in parallel: efficiency delivers reductions now, while fuels deliver the deeper cuts over a longer horizon.
What this means for charterers
For a charterer, decarbonisation shows up as a set of practical considerations rather than an abstract policy. Fuel efficiency is also cost efficiency, so a more efficient ship is usually a cheaper ship to run, and that interest is shared with the owner who pays the bunker bill under a voyage fixture or recovers it through the rate.
Speed is the clearest shared lever. Because slow steaming cuts both fuel burn and emissions, the speed and consumption warranties written into a charter directly shape a ship’s carbon intensity. Those warranties feed the same fuel assumptions that sit behind charter rates and the daily economics of a time charter, so the commercial conversation and the emissions conversation are increasingly the same conversation. A ship’s CII rating and its EEXI standing are becoming part of vessel selection, alongside the usual questions of cargo fit, draught, and position.
The framework also nudges attention toward how efficiently time is used. Waiting at anchor with engines running, or steaming fast to make a date and then idling, hurts a ship’s operational rating. That puts a premium on tighter arrival planning and on routing across the trade lanes that a bulk carrier serves.
Scope and what this page does not cover
This page is a structural explainer of how dry bulk shipping decarbonises: the IMO framework, the efficiency levers, and the fuel options. It is not a tracker of current regulation, market levels, or fuel prices, and it deliberately avoids date-stamped figures because reduction targets, fuel costs, and adoption rates change and depend on local conditions.
It does not give legal or compliance advice on meeting EEXI or CII for a specific vessel, which depends on the ship’s particulars and class guidance, and it does not rank one alternative fuel as the right answer, because that judgement turns on route, ship design, fuel availability, and cost. For the regulatory detail, the authoritative source is the IMO under MARPOL Annex VI and the 2023 IMO GHG Strategy. For the commercial mechanics that sit alongside these measures, see the related pages on chartering, bulk carriers, and dry bulk cargoes.