Projections of CO2 emissions and fuel mix for the global shipping fleet

We explore three different CO2 pathways for the world fleet, where the uptake of energy-efficiency measures, speed reduction, and alternative fuels are simulated based on costs, and on existing and imminent policies. Two are pathways to meet the IMO GHG ambitions, while one is what would happen under current policies. The results show that achieving the IMO ambitions is possible, but will require adoption of policies to promote development and uptake of alternative fuels. 

The demand for seaborne trade is projected to grow by 39% until 2050. The energy use per tonne-mile will decline by 35% to 40% on average towards 2050 in all projected pathways. This is due to energy-efficiency measures, mainly hull and machinery improvements, and speed reduction, which do not require further policies to promote uptake. 

In all modelled pathways, there is a prevalent use of liquefied methane (40%–80% of the 2050 fuel mix). Both fossil and non-fossil primary energy is used to produce the methane. Ammonia is the most promising carbon-neutral fuel option for newbuildings. Another alternative would be a gradual shift on existing ships relying on drop-in fuels compatible with current fuel converters (such as bio/electro-diesel replacing liquid fuels, or bio/electro-methane replacing LNG). The preference for ammonia is due to the lower cost of the converter, storage and the fuel itself compared with H2 and liquefied biogas (LBG)/synthetic methane. The share of carbon-neutral fuels in world fleet energy needs to be 30%–40% in 2050, in addition to improving energy efficiency, to achieve IMO GHG ambitions.

The 2050 fuel mix is heavily dependent on the specific design of the GHG regulations which are put in place, and on how fuel-converter costs (e.g. diesel engine, marine fuel cell) and fuel prices develop towards 2050. We find that minor changes to the underlying assumptions can significantly alter the outcome. Unless alternative fuels become price competitive with fossil fuels, introducing policy measures is a key component for addressing shipping GHG emissions. Figure 4 shows one possible pathway for international shipping achieving the IMO ambitions; here, regulations will gradually require all newbuilds from 2040 to be almost carbon-neutral.

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