Photo: ©Sky Sails

Shipping can and must do more

Greenhouse gas emissions from shipping could be cut by more than three-quarters with current technologies.

In 2012, international shipping was responsible for emitting 938 million tonnes of carbon dioxide (CO2), corresponding to 2.6 per cent of global emissions. According to the third greenhouse gas study by the International Maritime Organisation (IMO), shipping activity could double or even triple by 2050 under business-as-usual scenarios. Consequently, greenhouse gas emissions from ships could increase by between 150 and 250 per cent by 2050, if no further action is taken in this area.

However, a new scientific review of around 150 studies reveals that major potential exists for shipping to cut its emissions, and that many of the measures available would actually save the industry money because of the fuel savings incurred.

Together, if implemented, these measures could increase efficiency and reduce the emissions by more than 75 per cent against a 2050 baseline scenario. In terms of emissions per freight unit transported, emissions could come down by a factor of 4–6.

The authors identified a whole range of measures, which they grouped under five main categories: Hull design; Power and propulsion; Alternative fuels; Alternative energy sources; and, Operation (see figure).

Hull design measures focus primarily on utilising economies of scale and reducing resistance during operation, while power and propulsion includes e.g. hybrid drivetrains.

The highest CO2 reduction potential was found for the use of biofuels, but the authors point out that there are several issues around biofuels that need to be resolved, such as variations in CO2-reduction potential, the carbon neutrality assumption, and competition for scarce land resources.

While switching to LNG as a fuel could somewhat reduce CO2 emissions, it would increase emissions of the potent greenhouse gas methane. Moreover, a one-sided focus on LNG – which is a fossil fuel – risks lock-in of the sector into a high-carbon infrastructure.

Regarding alternative energy sources, the authors observe a high reduction potential for wind power but a low one for solar power. Shore-side electricity (cold ironing) has some potential, but it depends on how the electricity is produced. There is still little data available on fuel cells for power generation on-board ships.

Speed optimisation is classified as a measure that can achieve relatively high reductions in fuel consumption and emissions.

The different measures can be combined in many ways. One practical and economically feasible example is given in the study that would result in a 78 per cent emission reduction (using third-quartile reduction potential data). If biofuels are also included, the reduction potential increases to 85–96 per cent.

The authors conclude that there is potential for reducing ship emissions of CO2 by 75–85 per cent, i.e. a factor of 4–6 per freight unit transported, with current technologies and based on third-quartile values. If median values are used instead, an emission reduction of 50–60 per cent is said to be more realistic.

The IMO has for many years been under pressure from the European Union and the UN Framework Convention on Climate Change (FCCC) to come forward with concrete proposals to reduce the sector’s greenhouse gas emissions. The issue will be discussed further at a meeting with the IMO’s Marine Environment Protection Committee in April next year.

Christer Ågren

State-of-the-art technologies, measures and potential for reducing GHG emissions from shipping – a review. By Evert Bouman et al. Published in May 2017 in Transportation Research Part D. Link:

Figure: CO2 emission reduction potential from individual measures, sorted into five main categories



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