What the ETS actually does — and doesn't do

The EU ETS is a cap-and-trade system: a shrinking annual emissions ceiling, tradeable allowances worth one tonne of CO2 each, and a market-set carbon price that covered operators must pay if they don't cut emissions. Maritime transport was folded into it from 1 January 2024, covering all ships of 5,000 gross tonnage and above entering EU ports, regardless of flag. Coverage is asymmetric by voyage type: 100% of emissions on voyages between two EU ports and while a ship is at berth in an EU port, but only 50% of emissions on voyages that start or end outside the EU — the other half of an international leg falls outside EU jurisdiction. The financial obligation is phased in gradually: shipping companies pay for 40% of verified 2024 emissions, 70% of 2025 emissions, and the full 100% from 2026, with only CO2 counted through 2025 before methane and nitrous oxide are added to scope in 2026; the first allowance surrender deadline (covering 2024 emissions) was 30 September 2025. None of this requires a ship to change what it burns — it only makes burning more of it more expensive.

The actual monitoring backbone: MRV, not the ETS itself

The instrument that makes any of the above enforceable is the Monitoring, Reporting and Verification (MRV) Regulation (EU) 2015/757, amended by Regulation (EU) 2023/957 of 10 May 2023 specifically to extend it to cover the ETS's accounting needs. Ships already had to report fuel consumption and CO2 per voyage under the original 2015 MRV rules; the 2023 amendment widened that reporting to methane and nitrous oxide, extended MRV coverage from 2025 to smaller offshore and general cargo ships (400–5,000 GT) ahead of those same offshore vessels entering full ETS scope at 5,000 GT from 2027, and routes the resulting company-level verified data through the THETIS-MRV platform directly into ETS allowance-surrender calculations. In practice this means a ship's emissions are third-party verified and cross-checked against fuel purchase and consumption records before a single allowance changes hands — the ETS is a price mechanism sitting on top of an existing, independently audited data pipeline, not a monitoring system in its own right.

Where the actual fuel-switching mandates come from

Two separate regulations do the work the ETS often gets credit for.

The Sulphur Directive (EU) 2016/802. Since 1 January 2010, any ship of any flag berthed in an EU port must burn fuel with sulphur content no higher than 0.10% by mass — far below the 0.50% global cap that applies on the open ocean under IMO rules. A ship arriving with higher-sulphur fuel in its tanks has to run a fuel changeover operation, timed to start as soon as possible after arrival at berth and finish as late as possible before departure, so as little high-sulphur fuel as possible is burned dockside. This is compounded by Sulphur Emission Control Areas (SECAs) covering the Baltic Sea, the North Sea, and the English Channel, where the 0.10% limit applies throughout the whole sea area, not just at berth — meaning ships on that approach are switching fuel well before they're anywhere near a quay. Compliance is verified by the competent authority of each member state.

FuelEU Maritime (Regulation (EU) 2023/1805), fully in force since 1 January 2025, is the newer and stricter layer: it doesn't cap sulphur, it caps the greenhouse-gas intensity of the energy a ship burns, calculated well-to-wake against a fixed 2020 baseline. The cut steepens over three decades rather than landing all at once, and covers vessels above 5,000 GT calling at EU ports — by the Commission's own account, about 55% of ships calling at EU ports, representing roughly 90% of the sector's CO2 emissions.

Source: European Commission, FuelEU Maritime official page (transport.ec.europa.eu). Coverage mirrors the ETS's own asymmetric rule: 100% of energy used between two EEA ports and at berth, 50% on a voyage to or from a non-EU port. Operators had to submit monitoring plans by 31 August 2024, must log fuel consumption and OPS connections from 1 January 2025, and submit annual reports to accredited verifiers by 31 January each year, first due 31 January 2026.

Its most direct lever on fuel choice is a reward, not a penalty: renewable fuels of non-biological origin (e-methanol, e-ammonia, e-hydrogen, e-LNG, e-diesel, e-LPG, e-DME) get a multiplier of 2 applied to the energy they contribute when calculating a ship's GHG intensity from 2025 through 2033 — nominally counting each tonne of e-fuel as two, which lowers the calculated intensity and rewards early adoption. If RFNBOs haven't reached a 1% share of marine fuel by 2031, a mandatory 2% RFNBO sub-target kicks in for 2034, turning the current voluntary reward into a backstop mandate if uptake stalls.

The "green corridor" layer: two different things wearing the same name

"Green corridor" is doing double duty in current EU policy, and the two things it refers to aren't the same project.

TEN-T European Transport Corridors, established under the revised Trans-European Transport Network Regulation, merge the old Core Network Corridors and Rail Freight Corridors into nine unified freight corridors — mostly a land-and-inland-waterway infrastructure programme. The concrete maritime-adjacent piece is the Alternative Fuels Infrastructure Regulation (AFIR), in force since 13 April 2024, which sets a specific trigger for shoreside electricity (cold ironing/OPS): any EU port handling at least 50 port calls a year by large passenger vessels, or at least 100 by container vessels, must provide shore power capable of meeting 90% of average annual demand from those calls by 1 January 2030 — the same 2030 date FuelEU Maritime uses to start requiring container and passenger ships to actually plug in at AFIR-covered ports, extending to all OPS-equipped EU ports by 2035. A named example already under construction is the Rotterdam–Duisburg hydrogen pipeline, targeting 2027, feeding the Ruhr industrial cluster; a separate April 2025 agreement extends a liquid-hydrogen route from Duqm (Oman) through Amsterdam to Duisburg. Enforcement of the freight-visibility side runs through the Electronic Freight Transport Information (eFTI) Regulation, digitising freight documentation, mandatory across member states by July 2027.

The Global Maritime Green Corridor, by contrast, is a Global Gateway initiative led jointly by Denmark and the European Commission under a "Team Europe" framework, aimed specifically at long-haul shipping routes — connecting EU ports to strategically important ports elsewhere in the world and helping partner countries build bunkering infrastructure for renewable and low-carbon marine fuels at the other end of the voyage. As of the Commission's own page, it is genuinely still in the design phase: the Joint Research Centre is running a study on the criteria for ranking candidate ports, and no specific corridor route or port pair has been named yet. This is a meaningfully different thing from the AFIR/TEN-T corridors above — one is EU-internal freight infrastructure with binding 2025–2030 deadlines; the other is an outward-facing initiative for international shipping lanes that hasn't picked its routes.

The pilot layer feeding both: what's actually been built

A tier of EU-funded R&D projects sits underneath the policy layer, supplying the technology a fuel-switching or corridor mandate would eventually require. None of these are yet commercial-scale deployments; they range from delivered demonstrators to early development.

Source: CORDIS, "Discover the EU-funded projects putting the green into waterborne transport."

Reading the four pieces together

Put in order of what actually forces a ship to burn something different, rather than just pay more for what it already burns: the Sulphur Directive is the oldest and most concrete fuel-switching mandate, enforced since 2010 at every EU berth; FuelEU Maritime is the newer, broader mandate that will do more of the actual fuel-switching work over the next decade through its e-fuel reward multiplier and its 2031/2034 RFNBO backstop; the ETS is a carbon price riding on the same MRV data pipeline, making high-emission fuel choices progressively more expensive without mandating any particular fuel; and the green corridor initiatives — one already building pipelines on a fixed EU timeline, the other still ranking candidate ports abroad — are the infrastructure layer meant to make compliant fuel actually available where ships need to bunker it. The CORDIS-funded pilots are the technology bench everything else assumes will eventually scale.

Sources and caveats