◄Previous: 8 The path to fully decarbonised transport

# 8.1 International shipping

Shipping and aviation are ‘international’ topics and often get omitted from national transport policy considerations.

In 2023, globally CO2 emissions from shipping made up about 2.3% of the total (IEA, 2024). The bulk of the world’s shipping currently uses large highly efficient diesel engines. These usually run on heavy fuel oil which has the advantage of being cheap, but it can be highly polluting (an international limit of 0.5% sulfur content was introduced in 2020).

A range of options for decarbonisation have been suggested.

## Hybrid diesel-electric and full battery electric ships

For ships making short journeys, such as ferries, the weight of batteries may not be a serious problem. However, ports would need to introduce high capacity charging facilities.

A full battery electric ferry, the Aurora has been operating the 4 km crossing between Denmark and Sweden since 2018. The power ratings and battery capacity are about 100 times larger than those for a car. The Aurora has a 4.1 MWh lithium ion battery driving 6 MW of electric motors turning the propellers.

Video 1 Battery and charging system for an electric ferry

## Alternative fuels

Biofuels – the fuel flexibility of large diesel engines potentially means that ship biodiesel would not have to reach the same tightly specified standard as road vehicle or aircraft biofuel. But could large quantities be produced sustainably and at an acceptable cost?

Hydrogen produced from low carbon sources – this could be used directly with fuel cells. As described earlier, the volume of the hydrogen required could pose problems. A better solution might be to convert it to liquid ammonia, which could be burned in large internal combustion engines.

Wind power – various schemes for ‘wind assistive technologies’ have been proposed to add automatically deployed and controlled sails to large cargo ships.

And, of course, there is always the option of reduced international shipping movement by using more home-produced goods.

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