Decarbonisation Technology - November 2023 Issue

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

Total GHG emissions Mton CO 2 eq, (% change vs 2008)

Voyage based

Vessel based

2008 2012 2018



701 (-11.7%) 740 (-6.8%)

848 (-9.8%) 919 (-2.2%)

Table 2 Evolution of emissions from international shipping

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









2020 2015










Credit: Reproduced with the permission of the International Maritime Organization (IMO), which does not accept responsibility for the correctness of the material as reproduced: in case of doubt, IMO’s authentic text shall prevail. Readers should check with their national maritime Administration for any further amendments or latest advice. International Maritime Organization, 4 Albert Embankment, London, SE1 7SR, United Kingdom. Figure 1 Projections of maritime ship emissions as a percentage of 2008 emissions (IMO, 2021)


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