According to IMO:

​The proposed amendments to the MARPOL convention would require ships to combine a technical and an operational approach to reduce their carbon intensity​. This is in line with the ambition of the Initial IMO GHG Strategy, which aims to reduce carbon intensity of international shipping by 40% by 2030, compared to 2008.

For the records, the amendments were developed by the seventh session of the Intersessional Working Group on Reduction of GHG Emissions from Ships (ISWG-GHG 7), held as a remote meeting 19-23 October 2020.

Following there, the draft amendments will be forwarded to the Marine Environment Protection Committee (MEPC 75), to be held in remote session 16-20 November 2020.

In case they gain approval, the draft amendments could then be put forward for adoption at the subsequent MEPC 76 session, to be held during 2021.

The proposed MARPOL amendments are the following:

There are two new measures: the technical requirement to reduce carbon intensity, based on a new Energy Efficiency Existing Ship Index (EEXI); and the operational carbon intensity reduction requirements, based on a new operational carbon intensity indicator (CII).

The dual approach aims to address both technical (how the ship is retrofitted and equipped) and operational measures (how the ship operates).

In fact, attained and required Energy Efficiency Existing Ship Index (EEXI) is required to be calculated for every ship. This indicates the energy efficiency of the ship compared to a baseline.

Ships are required to meet a specific required Energy Efficiency Existing Ship Index (EEXI), which is based on a required reduction factor (expressed as a percentage relative to the EEDI baseline).

...IMO stated.

The proposals are for ships of 5,000 gross tonnage and above to have determined their required annual operational carbon intensity indicator (CII). The CII determines the annual reduction factor needed to ensure continuous improvement of the ship’s operational carbon intensity within a specific rating level.

The actual annual operational CII achieved (attained annual operational CII) would be required to be documented and verified against the required annual operational CII.

This would enable the operational carbon intensity rating to be determined.  The rating would be given on a scale - operational carbon intensity rating A, B, C, D or E - indicating a major superior, minor superior, moderate, minor inferior, or inferior performance level. The performance level would be recorded in the ship’s Ship Energy Efficiency Management Plan (SEEMP).

A ship rated D for three consecutive years, or E, would have to submit a corrective action plan, to show how the required index (C or above) would be achieved.

...IMO added.

Furthermore, the draft amendments would require the IMO to review the effectiveness of the implementation of the CII and EEXI requirements, by 2026 at the latest, and, if necessary, develop and adopt further amendments.

In light of the above, BIMCO expressed its concerns over IMO's development of new short-term measures, commenting:

"While the EEXI reduction rates are established and listed in the draft MARPOL amendments to be discussed at next month’s Marine Environment Protection Committee (MEPC) meeting, the CII rating mechanism still lack important details such as: how should carbon efficiency be measured, and which reduction factors should be used to calculate annual limits for CII for each ship?"

Concluding several associated guidelines also still need to be agreed before we can assess the impact of the proposed regulation on the fleet, BIMCO noted.