Reducing GHG emissions from international shipping

The International Maritime Organization’s revised strategy and future plans.

Eddy Van Bouwel
EvBo Consult

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Article Summary

The International Maritime Organization (IMO) holds responsibility for regulating emissions from international shipping. The IMO is a United Nations agency headquartered in London, and brings together 175 Member States (IMO, 2023). IMO established GHG reduction ambitions for the first time in 2018, when an initial GHG strategy was adopted (IMO, 2018). The initial strategy included the ambition to ‘reduce the total annual GHG emissions by at least 50% by 2050 compared to 2008, while, at the same time, pursuing efforts towards phasing them out entirely’. Importantly, the initial strategy included a commitment to review the strategy every five years. IMO’s Marine Environment Protection Committee (MEPC) was given a timeline to adopt a revised GHG strategy in 2023.

Revised IMO GHG Strategy
A revised strategy was adopted at the 80th session of the Committee in July 2023, significantly raising the level of ambition and the speed to reach net zero GHG emissions (IMO, 2023). The most significant change is the adoption of a net zero GHG target by or around 2050. In addition, indicative checkpoints have been added for 2030 and 2040, including the ambition to have at least 5% of the energy used to be from near-zero GHG technologies by 2030. The initial and revised strategies are summarised in Table 1.

Current emission levels and outlook to 2050
As all targets are expressed as percentage reductions vs 2008, it is interesting to look at the most recent emissions data vs 2008. IMO’s Fourth GHG study, published in 2020, provides an authoritative reference (IMO, 2021). Over time, different methodologies have been used to estimate GHG emissions from international shipping; two such methodologies were used in the Fourth IMO GHG report: vessel-based allocation and voyage-based allocation.

Vessel-based estimation uses vessel characteristics combined with assumptions of typical operations by vessel type to estimate total emissions. This methodology was used in earlier IMO GHG assessments.

Voyage-based estimation uses actual voyage data combined with vessel characteristics. This obviously requires a lot more data and data processing but should yield a more accurate estimate of total emissions.

While there is a significant difference in the results of both methods in terms of assessing progress towards the new IMO GHG targets, the most important point is to look at the numbers on a consistent basis. To that purpose, the 4th IMO GHG report includes a reassessment of the 2008 emissions based on the new estimation methods. Table 2 summarises the main GHG emissions estimate numbers reported by the 4th IMO GHG study.

In the absence of further regulations, emissions are projected to increase from about 90% of 2008 emissions in 2018 to 90-130% of 2008 emissions by 2050 for a range of plausible long-term economic and energy scenarios (see Figure 1). The current projections are significantly lower than earlier ‘Business As Usual (BAU)’ estimates. For example, the BAU scenarios considered in the Third IMO GHG study (IMO, 2015) projected an increase in emissions by 50% to 250% in the period to 2050.

As historically different methodologies have been used to estimate total GHG emissions from international shipping, measuring progress towards IMO’s targets will be less straightforward than one would expect.

IMO’s ability to assess global emissions, however, should further improve through the implementation of the Data Collection System (DCS) (IMO, 2016). Starting from January 1, 2019, ships of 5,000 gross tonnes (GT) and above are required to collect and report fuel consumption data for each type of fuel oil they use. The reporting process includes a third-party verification step. This should allow IMO to produce more accurate estimates of emissions. Obviously, the 2008 reference emissions will need to be reassessed to ensure a consistent basis for measuring progress towards IMO’s GHG strategy targets.

Carbon Intensity
Carbon intensity (CI) is a measure of ship efficiency in relation to the cargo carried, assessing GHG emissions per ton-mile of transport work. It can be measured in two ways: relative to the ship’s cargo carrying capacity, referred to as the Annual Efficiency Ratio (AER) and measured in gram CO₂/Dwt/nm (where Dwt = dead weight tonnage), or, relative to actual cargo carried, referred to as the Energy Efficiency Operational Indicator (EEOI) and measured in gram CO₂/ton cargo/nm.
The IMO Fourth GHG report has estimated CI improvements relative to 2008 for both CI indicators and based on the two emission inventory methodologies discussed above. The results are summarised in Table 3.

CI has clearly improved quite substantially since 2008. It is interesting to note that the largest improvements apparently happened between 2008 and 2012. This was when the first energy efficiency measures were being discussed at IMO. From 2012 onwards, annual improvements appear to settle in the 1-2% per year range. The difference between vessel-based and voyage-based CI numbers is directionally consistent with the observed differences in total emissions estimates between the two methods. The difference between AER and EEOI numbers is striking. This undoubtedly reflects the effect of so-called ballast voyages, when ships travel empty between ports while pursuing new cargo, and partial load voyages.

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