Countdown is back.

This time, we’re diving deep into the International Maritime Organization Net-Zero Framework (IMO NZF), starting with what it is, how it works, and what it will mean for the industry. This series will unpack elements of the regulation with explanations, analysis, and practical insights.

• The IMO NZF will become a new chapter under MARPOL Annex VI if adopted at MEPC/ES.2 in October 2025.

• The regulation must go through a process of adoption and tacit acceptance before entry into force.

• A series of guidelines need to be developed by 2028 for effective implementation of the IMO NZF.

• Understanding these IMO processes will help the industry prepare for the first year of reporting from 1 January 2028.

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With the IMO NZF on the horizon, businesses need to understand what is coming and when to make decisions based on regulations that will have a significant impact on their operations. Here we explain what we know about how the IMO process works and what it will take for the IMO NZF and associated guidelines to enter into force. This can enable the maritime industry to understand the framework’s complexities, identify challenges and opportunities, and determine the right time for action.

The IMO has been the international forum for developing regulations to protect the marine environment from the impacts of shipping since the 1970s. Over the past decade, the IMO has expanded its focus to the reduction of GHG emissions from shipping. The latest development in this area is the IMO NZF, which adds a new chapter to the main convention governing pollution from international shipping.

The International Convention on the Prevention of Pollution from Ships (MARPOL) is the main international convention for regulating pollution of the marine environment from ship operations and accidents. It was developed after pressure grew to regulate environmental pollution from ships following a series of tanker accidents including Torrey Canyon (1967), Argo Merchant (1976), and Hawaiian Patriot (1977). The original convention was adopted at the IMO in 1973 and was later integrated into the 1978 MARPOL Protocol, which entered into force on 2 October 1983.

The Convention has been amended many times over the years and now contains six technical Annexes (see Figure 1), including MARPOL Annex VI on “Regulations for the prevention of air pollution from ships”. Annex VI was added by a Protocol adopted in 1997 and entered into force on 19 May 2005. If the IMO NZF is adopted in October 2025, it will constitute a new Chapter 5 in MARPOL Annex VI.

Figure 1: Overview of the MARPOL Annexes arranged in order of entry into force. The IMO Net-Zero Framework will be a new chapter under Annex VI.

New regulations for existing conventions are developed as amendments. Amendments to MARPOL fall under the responsibility of the Marine Environment Protection Committee (MEPC), a technical committee of the IMO responsible for developing and adopting environmental regulations in international shipping. The MEPC usually meets 1-2 times per year. Once IMO Member States agree to an amendment and approve it in an MEPC meeting, MARPOL requires the IMO Secretariat (the administrative arm of the IMO) to circulate the amendments to the IMO Member States and allow six months for consideration. Following this period, the amendment can be adopted at the next MEPC meeting.

In the past, a cumbersome ratification process meant that approved amendments to IMO Conventions were slow to be adopted. This process required explicit consent from two-thirds of Member States for an amendment to enter into force. This would involve each Member State acting within their governments to ratify the amendment. The process could take many years or fail entirely, as happened with amendments to the Convention for the Safety of Life at Sea (SOLAS) between 1966 and 1973 that never entered into force.

To improve this situation, a procedure known as “tacit acceptance” is generally used by IMO organs to ensure efficient entry into force of amendments to existing conventions. Under tacit acceptance, an amendment enters into force without explicit consent from state parties when a certain period of time has passed without objection by a certain number of Member States. This is particularly important in the policy domains of shipping safety and environment, where rapidly changing technological developments demand frequent updates and new regulations.

As shown in Figure 2, the IMO NZF was approved as draft amendments to MARPOL Annex VI at MEPC 83 in April 2025. The IMO normally makes decisions by consensus, so it was unusual for a vote to be called for on this occasion. In total, 103 states voted, with 63 yes votes, 16 no votes, and 24 abstentions. As abstentions are not counted, this vote met the requirement for a simple majority of 40. With 176 Member States in the IMO, these voting numbers may seem low at first glance. However, based on credentials and voting rights, only 118 states were eligible to vote, and 15 of these were absent on the day of the vote.

In April, the Secretariat circulated the IMO NZF as draft amendments to Member States for consideration. An extraordinary session of MEPC (known as MEPC/ES.2) in October 2025 marks the end of the 6-month consideration period and is where the amendments will be presented for adoption. While adoption is also typically done by consensus, with a vote taking place in April, another call for a vote is likely to take place at MEPC/ES.2. Only states party to MARPOL Annex VI are entitled to vote on adoption, and at least a two-thirds majority is required for the amendments to be passed.

Who may vote on adoption? MARPOL Annex VI currently has 108 contracting states, comprising around 95% of the global fleet. States can become party to a protocol via ratification, acceptance, approval, or accession. This step can take several years and is completed when a state signs the necessary legal instrument and delivers it to the Secretary-General of the IMO.

Assuming adoption at MEPC/ES.2, the IMO NZF amendments enter into force automatically on 1 March 2027, unless objections are made by a specified number of parties. For MARPOL amendments, the acceptance period is a minimum of 10 months and is determined by the MEPC at the time of adoption. The amendment is accepted unless during that period more than one-third of Member States party to MARPOL Annex VI, or with a combined gross tonnage of at least 50% of the world’s merchant fleet, formally communicate an objection to the amendment. Following deemed acceptance, the amendments enter into force six months later. While the NZF is expected to enter into force in 2027, in effect ships will need to start complying from 1 January 2028, which is when the first reporting period begins.

Figure 2: A timeline of the IMO Net-Zero Framework from approval to first reporting period. Approval occurred in April 2025, with adoption in October as the next step.

When a government decides to formally join (i.e., to ratify) MARPOL or any other IMO convention, it also agrees to implement the convention in national law and enforce the rules. However, amendments may lack details needed for enforcement and compliance by ships. Guidelines fill this gap by providing the detailed technical guidance and description required for implementation and compliance. With complex and highly technical regulations, guidelines are key to ensuring global, uniform, and effective enforcement.

In principle, guidelines are soft law and thus not mandatory. Flag states can deviate from guidelines on a case-by-case basis when justified. However, states party to a convention can agree that full effect will be given to guidelines with mandatory legal status – so, in practice, IMO guidelines are widely followed.

Compared with amendments, guidelines are also more flexible to develop and test as pieces of regulation. This is because changes to guidelines can be effective immediately, whereas amendments must go through the tacit acceptance procedure. In addition, guidelines often end up becoming hard law following a test period.

The realm of IMO safety regulations provides an illustrative example. Here, guidelines are developed and adopted as interim guidelines in the first step. As the next step, they become guidelines. In the third step, the guidelines may become mandatory through amendments to a convention or a code. This whole process takes a few years and allows the guidelines to be tested by the industry and adapted to ensure that they are robust enough to go through the tacit acceptance procedure in the last step.

Draft guidelines, like those to be developed for the IMO NZF, will go through a development and consideration phase before finalization and adoption at the IMO. This work is often done in between IMO meetings by written communication in so-called ‘correspondence groups’ that MEPC establishes for a specific task and period. Correspondence group participation is open to all IMO Member States and observer organizations that have relevant expertise or a particular interest in the topic at hand. IMO observer organizations support the work of the IMO in this process, providing technical assistance and expertise in the development of the guidelines.

A so-called “lead country/organization” or the Secretariat will be designated to coordinate the work of the correspondence group, and terms of reference are agreed on by the relevant Committee or Sub-committee. The output of a correspondence group is a consolidated draft text on the guidelines reflecting the information received from participating members. Reports are submitted to the relevant parent body in advance of meetings. As per Convention amendments, only the Member States have the final say in approving or adopting guidelines. Guidelines are either approved by a Committee and circulated as a Circular letter or adopted and issued as a Committee resolution.

For the IMO NZF, approximately sixteen guidelines are to be developed or revised (see Table 1). The IMO Secretariat has prepared a draft work plan (see Figure 3) to be considered by the MEPC at its extraordinary session in October 2025. The guidelines will be developed from 2025 to 2027 across MEPC/ES.2, 84, 85, and 86. These guidelines can be grouped under six categories, shown in Table 1.

Table 1: Summary and scheduled adoption of guidelines under development and revision as part of the IMO Net-Zero Framework.

Meanwhile, the IMO Net-Zero Fund will be developed in parallel to guidelines, and the Secretariat may work on the internal setup and the development of draft governing provisions. All but two guidelines are scheduled for adoption by MEPC 85 in November 2026. The exceptions are the guidelines on recognition of certification schemes and reporting (due for adoption at MEPC 84 in May 2026), and the guidelines for determining the IMO GFI Registry administration fee (due at MEPC 86 in the first half of 2028).

Further clarity on the development of the guidelines is expected following the ISWG-GHG 20 meeting in October 2025. There is a lot of work and not much time, with the first reporting period beginning 1 January 2028.

In addition to guidelines, the IMO must complete work in several other areas of the IMO NZF. These include development of the IMO Net-Zero Fund, procedures for Port State Control, and the mechanism for setting and reviewing the price of Remedial Units. See Figure 3 below for a simplified overview of the process.

A draft work plan has been submitted by the Secretariat and will be reviewed by Member States at MEPC/ES.2 in October.

Figure 3: Overview of the key workstreams for developing the IMO Net-Zero Framework over the coming years. Figure adapted from the draft work plan in document MEPC/ES.2/3. Workstreams for energy efficiency and short-term measures have been excluded. GFI = GHG fuel intensity, ZNZs = zero or near-zero GHG emission technologies, fuels, and/or energy sources, III = Implementation of IMO Instruments, RU = Remedial Unit (the penalty for non-compliance), ISWG-GHG = Intersessional Working Group on Reduction of GHG Emissions from Ships, GESAMP = Group of Experts on the Scientific Aspects of Marine Environmental Protection, LCA = life-cycle analysis.

In this latest Countdown series, we will examine various aspects of the IMO NZF, including forthcoming guidelines. With this series, we aim to create clarity for the industry and provide insights for IMO policymakers as they further develop the historic regulation.

• The full text of the draft Revised MARPOL Annex VI 2025 can be found in document MEPC/ES.2/2 on IMODOCS (registration required). An older version following approval at MEPC 83 is publicly available. See Chapter 5 for the IMO NZF. 

• The 2022 Consolidated Edition of MARPOL can be purchased from the IMO publications website here.

• Guidelines will be published on the IMODOCS platform (registration required) as either circular letters or resolutions. Guidelines for the IMO NZF are expected to be published as resolutions. Resolutions can also be accessed via the IMO website here. An up-to-date index of MEPC resolutions and guidelines related to MARPOL Annex VI is available here.

• The IMO website is also a useful resource for following the latest developments, learning about the organization’s functions, and accessing IMO publications.

• For a full overview of the draft workplan for the implementation of the IMO NZF, see document MEPC/ES.2/3 on IMODOCS (registration required).

Authors: Reuben Carey (MMMMCZCS) and Pernille Palmelund Sørensen (MMMMCZCS)