The IMO Carbon Intensity Indicator (CII) regime has applied to ships of 5,000 GT and above on international voyages since 1 January 2023. For most owners, the first three years were manageable — the required reductions were modest, and a vessel that was operationally reasonable tended to land at a C rating without dramatic intervention. That changes in 2027, and the reason is a set of numbers adopted at MEPC 83 in April 2025.

The reduction trajectory steepens sharply

CII works by comparing a vessel’s attained annual carbon intensity against a required value. That required value tightens each year through a reduction factor — the “Z-factor” — measured against a 2019 baseline. Through 2026 the trajectory was gentle and linear:

  • 2023: 5%
  • 2024: 7%
  • 2025: 9%
  • 2026: 11%

Resolution MEPC.400(83), adopted on 11 April 2025, set the figures from 2027 onward — and they do not continue the gentle two-points-a-year pattern. They accelerate:

  • 2027: 13.625%
  • 2028: 16.25%
  • 2029: 18.875%
  • 2030: 21.5%

The jump from 11% to 13.625% in a single year is larger than any step before it, and each subsequent year adds another 2.625 points. By 2030 the required intensity is more than double the reduction demanded in 2026.

What this does to your ratings

The practical effect is rating drift. A vessel comfortably rated C in 2026 — with no operational changes at all — can find itself rated D in 2027 and trending toward E by the end of the decade, simply because the goalposts moved. The vessel did not get worse; the standard got harder.

This matters because the rating is not cosmetic. Under MEPC.347(78), a vessel rated D for three consecutive years, or E for a single year, must develop a corrective action plan as part of its SEEMP Part III. Beyond the regulatory obligation, the commercial consequences compound: charterers increasingly screen on CII rating, financiers reference it in lending terms, and the Poseidon Principles banks and Sea Cargo Charter signatories are tightening their own portfolio expectations.

The deadline most owners have already missed

There is a deadline that quietly passed for many operators. The SEEMP Part III implementation plan covering the 2026–2028 period needed to be revised and approved by 31 December 2025. If your vessel’s SEEMP Part III still reflects the pre-2025 figures, it is out of date — and an out-of-date implementation plan is exactly the kind of finding that surfaces at the wrong moment during a port-state inspection or a charterer’s due diligence.

What owners should be doing now

The 2027 inflection is close enough that operational measures alone may not close the gap for older or less efficient tonnage. We would suggest three steps:

First, get an honest baseline. Calculate where each vessel actually sits today and project its rating forward against the new Z-factors — not against the 2026 standard it is currently meeting. A vessel’s 2027 rating is the number that matters for planning.

Second, separate operational from structural fixes. Slow steaming, weather routing, hull cleaning, and voyage optimisation all help, but they have practical and commercial limits. For some vessels, the 2027 gap is only closable through structural intervention — and it is far better to know that in 2026 than to discover it after two years of declining ratings.

Third, make the SEEMP Part III a real document. Not a box-ticked template, but a genuine implementation plan that an inspector or charterer would find credible.

You can see roughly where any vessel lands under the new factors using our free CII Calculator, which is built on the MEPC.400(83) values. For a fleet-wide gap analysis and a credible compliance trajectory — including where the Manus-Zim Modular Hybrid Protocol can deliver structural improvement — our Marine Survey & Compliance practice can help.