• The IMO LCA Guidelines play a key role in the IMO Net-Zero Framework by allowing companies to estimate the well-to-wake GHG emission factors for marine fuels. 

• The 2024 LCA Guidelines are the latest version, covering the assessment of marine fuels' life cycle GHG intensity –  including scope, methodology, emission factors, and the need for verification and certification. 

• Emission factors are values that represent the GHG emissions per energy unit of fuel and are used in determining vessels’ compliance with the IMO Net-Zero Framework. 

Not a subscriber yet? Sign up for Countdown newsletters here.

For industry, the IMO LCA Guidelines will be a key building block in the business case for low-emissions maritime energy. Companies ranging from fuel producers to shipowners and operators must familiarize themselves with the IMO’s LCA methodology and associated emission factors. Even minor changes in emissions intensity can have a significant impact on a ship’s compliance cost.

Life cycle analysis (LCA) is used by policymakers to evaluate the environmental aspects of products, processes, and services across production, transportation, use, and disposal (hence “life cycle”). In the context of the IMO Net-Zero Framework (IMO NZF), the IMO LCA Guidelines define how the life cycle GHG emission factors of marine fuels and energy carriers are assessed. These emission factors are used to calculate a ship’s attained annual GHG fuel intensity (GFI) and the extent to which it meets, exceeds, or misses the targets set by the IMO NZF (see Figure 1). The 2024 LCA Guidelines are the latest version of the IMO LCA Guidelines, adopted at MEPC 81 in March 2024.  

The 2024 LCA Guidelines are organized into five chapters covering scope, methodology, emission factors, verification, and certification, as well as the review process for further development of the Guidelines. In this edition of Countdown, we’ll look at the scope, methodology, and default emission factors in the guidelines, while verification and certification will be covered in future editions. 

Figure 1: A conceptual diagram showing how the IMO LCA Guidelines fit within the IMO Net-Zero Framework (IMO NZF).

The 2024 LCA Guidelines use ISO standards 14044: 2006 and 14040: 2006 as the basis for the methodology, principles, framework, and quantification of GHG emissions. These two ISO standards, which are widely used by voluntary reporting frameworks and policymakers, provide guidance on each phase of the LCA as well as the overall process. 

The 2024 LCA Guidelines are still under development, with revised versions expected to be adopted at MEPC 84 (May 2026) and MEPC 87 (first half of 2028).

The MEPC is responsible for adopting updates to the Guidelines, building on proposals from IMO Member States and observer organizations, and receiving scientific guidance from the GESAMP LCA working group (GESAMP-LCA WG).  

GESAMP stands for the Group of Experts on the Scientific Aspects of Marine Environmental Protection. It was originally established in 1969 as an advisory body to the UN system.  

The GESAMP-LCA WG is the 46th GESAMP group, set up by the IMO in 2024 and consisting of twelve experts. The group is responsible for scientific review and continuous development of the IMO LCA Guidelines.

Table 1: The building blocks of the IMO LCA Guidelines which come from the 2024 LCA Guidelines. These key elements are used to determine the emission factors of energy used in ships.

The 2024 LCA Guidelines include a methodology for calculating the GHG emission factors of marine fuels, specifically focusing on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). As shown in Figure 2, the Guidelines define the well-to-tank (WTT) stage as emissions from feedstock extraction/cultivation/acquisition/recovery, conversion to fuel, transportation and bunkering, while the tank-to-wake (TTW) stage covers the onboard combustion and conversion of fuel.

Figure 2: A breakdown of the system boundaries, or what is included in each stage of the life cycle analysis.

The WTW GHG emission factor of fuels is expressed in grams of CO2 equivalent per megajoule (gCO2eq/MJ). The term "equivalent" here refers to standardization of the three covered GHGs (CO2, CH4, and N2O) to the climate impact of CO2. 

These emission factors are used to calculate ships’ attained annual GFI, as described in Regulation 33 of the IMO NZF. The emission factor of the fuel is multiplied by the annual energy consumption of that fuel to obtain a ‘GFI compliance balance’, converting intensity values into total GHG emissions in terms of tonnes CO2eq. 

A compliance balance that is in deficit (meaning that the GFI is too high) must be addressed through purchasing Remedial Units or Surplus Units from other ships.  

The 2024 LCA Guidelines also include ten sustainability themes or aspects, each with its own objective and metric. The criteria are limited to the environmental impacts of fuel production and consumption, covering elements such as air, water, and resources quality and/or availability, as well as the impact on changing land use. These themes are broadly described and are pending further guidance to be developed by the IMO.  

The 2024 LCA Guidelines also include the concept of the ‘Fuel Lifecycle Label’ (FLL). The FLL is a technical tool that includes all the information relevant to the LCA assessment of marine fuels and energy carriers: 

• Fuel type 

• Feedstock (feedstock type and feedstock nature or carbon source) 

• Conversion or production process (process type and energy used in the process) 

• GHG emission factors 

• Information on fuel blends  

• Information on sustainability themes or aspects 

We don’t yet know exactly how the FLL will be combined with certified information from the fuel production supply chain and the bunker delivery note (BDN). Guidelines addressing these elements are scheduled to be adopted by MEPC 85 in November 2026.

Emission factors used in the context of the IMO LCA Guidelines can be default or actual. Here, we break down how each type of emission factor is used in the 2024 LCA Guidelines. 

In the IMO LCA Guidelines, default emission factors provide standardized GHG intensity values to be used directly when calculating attained GFI.  

The 2024 LCA Guidelines cover no fewer than 128 different fuel or energy carrier pathways, along with 14 fuel groups that include some default emission factors. Out of this list of 128, only three currently include full WTW values.  

To determine default GHG emission factors, the GESAMP-LCA WG are applying “representative” and “conservative” assumptions to account for regional differences in feedstock pathways, onboard ship conditions, and the performance of energy converters (e.g., engines). 

At MEPC 83, the GESAMP-LCA WG was tasked with developing a uniform understanding of the terms “representative” and “conservative” for the assessment of default emissions for MEPC 84 in Q2 2026. The aim of using “representative” and “conservative” default factors is to set realistic values that incentivize economic operators to demonstrate lower emissions by using actual emission factor.  

IMO Member States could submit proposed default emission factors to the group for review until August 2025. As shown in Figure 3, future windows of opportunities for submitting default emission factors are expected.

Figure 3: Timeline for default emission factor review and approval. Adapted from draft work plan in document MEPC/ES.2/2 on IMO DOCS.

Upon approval, these default emission factors will be submitted as part of the group’s final report and considered for approval and inclusion in the IMO LCA Guidelines by the MEPC. More about the submission, review, and recommendations for emission factors can be found in MEPC Circular 916 from April 2025. 

Under the 2024 LCA Guidelines, economic operators can submit actual emission factors for verification and certification in cases where their GHG performance is superior (lower emissions) to the default values. The three critical points in this process are:  

1. The methodologies to calculate the actual GHG emission factor must follow the 2024 LCA Guideline methodologies under development for both WTT and TTW emission factors.  

2. Fossil fuel pathways are excluded from applying for actual WTT emissions, unless the fuel production includes carbon capture and storage or utilization and storage (CCS/CCUS) – i.e., so-called “blue fuels.”  

3. All fuel pathways are allowed to use actual TTW GHG emission factors.  

However, the verification and certification methodologies required for all three points still need to be developed.

Figure 4 illustrates the use of default values from the 2024 LCA Guidelines to calculate a fuel’s GFI. In this example, we use heavy fuel oil (HFO) with very low sulfur, one of the three pathways with values in the Guidelines and the most widely used fuel type for international commercial shipping.

Figure 4: An example of how to calculate the emissions intensity of heavy fuel oil with very low sulfur, based on the inputs and methodologies found in the 2024 LCA Guidelines.

This example with HFO is a good starting point for understanding calculation methodologies. Other fuel types involve more complex calculations, as they incorporate elements such as emissions associated with land use, the impact of fugitive gas emissions that leak from supply chain processes, and methane slip (fuel that escapes from the energy converter without being oxidized).

To ensure the IMO LCA Guidelines are fully implementable and operational, IMO Member States must address some key aspects that require further development. These include defining and accounting for co-products and by-products, classification of waste and residues, and further guidance on the assessment of sustainability themes/aspects. System boundaries also need further clarification, particularly regarding the inclusion of avoided emissions, infrastructure, and pilot fuel use, among others. Addressing these gaps will be crucial for effective application and compliance with the IMO LCA Guidelines.  

Additionally, key parameters in the IMO LCA calculation methodology are still pending guidance, such as:  

• Emissions related to direct land-use change (‘el’ in the LCA formula) 

• Emissions credits related to improving agricultural management (esca) 

• Factor related to carbon source from captured CO2 as carbon stock to produce synthetic fuels (SFccu)

• Emissions credit from the use of captured CO2 as carbon stock to produce synthetic fuels (Eecu) 

• Emissions credit from the use of onboard carbon capture, OCCS (Eoccs) 

• Percentage of fuel emitted as fugitive emissions on board ship (Cfug)

The IMO LCA Guidelines are more than a technical document: they define the emissions accounting rules that determine compliance, regulatory costs, and market access under the IMO NZF. While details are continuing to evolve, understanding how the IMO LCA Guidelines work can help companies prepare for 2028 with a strategy that can lower emissions as well as compliance costs. 

Authors: Francielle Carvalho, Reuben Carey, Clémentine Hourtiguet, Harshil Desai, Joe Bettles (all MMMCZCS).