The International Maritime Organization (IMO) has introduced the 2024 Life Cycle Analysis (LCA) Guidelines as a foundational component of its Net-Zero Framework (IMO NZF). These guidelines establish the methodology for calculating the full life cycle greenhouse gas (GHG) emission factors of marine fuels, a critical step for the industry’s transition to low-emissions energy.
Role within the IMO Net-Zero Framework
The LCA Guidelines define how the well-to-tank (WTT) and tank-to-wake (TTW) GHG emissions of fuels are assessed. These calculated emission factors are expressed in grams of CO2 equivalent per megajoule (gCO2eq/MJ), standardizing the climate impact of CO2, CH4, and N2O. These factors are then used to calculate a ship’s attained annual GHG Fuel Intensity (GFI).
Ships that run a GFI deficit (meaning their GFI is too high) must address this imbalance by purchasing Remedial Units or Surplus Units from other vessels, demonstrating how even minor changes in emissions intensity can directly affect a ship’s compliance cost.
Scope and Methodology
The 2024 Guidelines, adopted at MEPC 81 in March 2024, are structured into five chapters covering scope, methodology, emission factors, verification, and certification. The methodology is based on the widely used ISO standards 14044 and 14040.
- System Boundary: The guidelines break down the fuel pathway into two stages. The WTT stage includes emissions from feedstock acquisition, conversion to fuel, transportation, and bunkering. The TTW stage covers onboard combustion and energy conversion.
- Scientific Development: The ongoing development and scientific review of the Guidelines are led by the Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) LCA working group, a body established by the IMO and consisting of twelve experts.
Default and Actual Emission Factors
The guidelines use both default and actual emission factors to determine compliance:
- Default Factors: These provide standardized GHG intensity values for use in GFI calculations. The 2024 Guidelines identify 128 different fuel pathways, though only three currently have full WTT/TTW values. The GESAMP group is tasked with applying “representative” and “conservative” assumptions to these factors to set realistic values and incentivize economic operators to pursue lower, verifiable emissions.
- Actual Factors: Economic operators can submit actual emission factors for verification and certification if their fuel’s GHG performance is superior (lower emissions) to the established default values. This option is available for all fuels’ TTW emissions, but for WTT emissions, it is primarily limited to non-fossil fuel pathways or “blue fuels” that incorporate carbon capture and storage/utilization and storage (CCS/CCUS). The specific verification and certification methodologies for these actual values are still under development.
Future Components
The 2024 LCA Guidelines also introduce two concepts pending further detailed guidance:
- Sustainability Themes: Ten broad environmental impact themes, such as air/water quality and resource availability, are included, but specific guidance and metrics are still being developed.
- Fuel Lifecycle Label (FLL): This is a technical tool designed to compile all relevant LCA information about marine fuels, including fuel type, feedstock, production process, emission factors, and sustainability information. Guidelines detailing how the FLL will integrate with the supply chain and bunker delivery documentation are scheduled to be adopted in November 2026 (MEPC 85).
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Source: Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping
