The carbon position of every ship, voyage by voyage.

Each ship gets an annual carbon-intensity rating from A to E. The attained figure is the year’s CO₂ in grams divided by the ship’s capacity, deadweight tonnes for cargo ships and gross tonnage for ro-ro and passenger ships, times nautical miles sailed.

The required figure is the ship type’s reference line cut by the year’s reduction factor, 11 % for 2026 and rising each year to 21.5 % in 2030. The rating comes from how far the attained sits from the required, on boundaries set per ship type.

The fleet sits on one ladder, each vessel’s attained figure set against its required line with the A to E band edges for its ship type. The attained figure is recomputed from the vessel’s own noon reports, fuel by grade and distance sailed, and a chip flags an entered figure that drifts from it.

Beneath the ladder, the IMO DCS card totals the year’s distance from the same reports.

A voyage between two EEA ports is in scope for all of its emissions. A voyage between an EEA port and one outside is in scope for half. A voyage between two non-EEA ports is out of scope.

The obligation was phased in, 40 % of in-scope emissions for 2024, 70 % for 2025 and 100 % from 2026. From 2026 methane and nitrous oxide count alongside carbon dioxide. Allowances for a reporting year are surrendered by 30 September of the following year.

Each voyage leg, load port, discharge port and fuel burned by grade, is stored with its three multipliers kept separate (tonnes of CO₂-equivalent, scope share, phase-in share), so a verifier can reproduce the allowance figure without reading code.

The year’s position runs as one bar, surrendered, covered by holdings and short, over a runway to the surrender deadline. Each leg moves through draft, submitted, verified and surrendered.

The greenhouse-gas intensity of the energy a ship uses, well-to-wake in grams of CO₂-equivalent per megajoule, must sit under a target that steps down from the 2020 baseline of 91.16, by 2 % from 2025, 6 % from 2030, 14.5 % from 2035, and on to 80 % from 2050.

A ship above the line carries a compliance deficit and pays €2,400 per tonne of VLSFO-equivalent energy, 10 % more for every consecutive year it misses. Article 20 lets a surplus be banked or a limited advance borrowed from the next year. Article 21 lets ships pool their balances, and the pool complies if its sum is at or above zero.

Each vessel’s energy-weighted intensity is computed from its in-scope fuel by grade, with verified certified batches blended in at their own intensity, and set against the year’s target to give a compliance balance in grams of CO₂-equivalent.

The glidepath draws the Article 4 staircase from 2025 to 2050 with the fleet’s mix as a line across it, so the crossing year reads directly. The pool desk aggregates balances under Article 21, prices a deficit against the penalty or a quoted external pool price, and an optimiser searches for the cheapest valid pool membership and says when its answer is a heuristic.

The UK scheme is separate from the EU one and reaches UK-domestic voyages only. A voyage between two UK ports is in scope for all of its emissions; an international voyage, including one to the EEA, is out of scope. Carbon dioxide, methane and nitrous oxide count from the first day.

Voyages between Northern Ireland and Great Britain are reported in full but surrendered at half. The scheme’s dates are listed beneath.

The obligation in UK allowances is computed from the same voyage legs as EU ETS and shown beside the EU ETS position whenever a year has UK-domestic legs. Holdings of UK allowances are not yet tracked. Each leg’s ports are matched to the seeded port list; UK-domestic legs are kept; 2026 legs that start before 1 July are counted as outside the first scheme year; and legs whose ports do not resolve are counted as unresolved rather than guessed in or out.

One thing the legs model does not yet capture is emissions at berth, which the scheme also covers. The screen says so.