IMO regulations could increase cruise ship CO2 emissions

The way IMO has formulated its Carbon Intensity Index may have a counterproductive effect for cruise ship CO2 emissions, writes Markus Aarnio, Chief Naval Architect, Foreship*.

While attention has been focusing on the International Maritime Organization’s Energy Efficiency Index for Existing Ships (EEXI), a mandatory Carbon Intensity Indicator (CII) is also planned for all ships above 5,000 GT (subject to MEPC76 adoption in June 2021).
In CII, ships are given a rating of A to E based on their annual CO2 emission and annual travelled distance. Ratings of A to C are considered acceptable but if the ship receives a rating of D or E a corrective action plan needs to be developed and approved so that at least a rating of Cis achieved. Today, the plan is for CII to be in force in 2023, although it should also be noted that rating thresholds are expected to get continually more stringent towards 2030.

The planned formula for CII for cruise ship’s is as follows (for cargo ships the formula uses DWT instead of GT):

CII= Annual CO2 emissions (g) / Gross Tonnage x Annual distance travelled (nlm)

For cargo ships, which need to transport cargo from point A to B, this formulation makes sense. However, for passenger cruise ships, the situation can be very different because cruise ships do not really need to do any transportation work. In a seeming paradox, in this case achieving a better CII rating can lead to increased fuel consumption and thus increased CO2 emissions.