Go slower to go greener

The overcapacity in the cargo fleet creates an opportunity to reduce ship emissions by simply sailing slower.

Current overcapacity in the ship fleet presents a golden opportunity for the global shipping industry to make quick and substantial reductions in emissions.

A new report1 assessing the potential of the shipping industry to cut its emissions of the main greenhouse gas (GHG) carbon dioxide has concluded that if the main shipping sectors make full use of existing fleet overcapacity they could reduce emissions by as much as a third, or up to 255 million tons per year, over the next three years.

Sailing at slower speeds improves operational efficiency and reduces fuel consumption. According to the study, a 10 per cent reduction in ships’ speed corresponds to a drop in fuel use – and an accompanying drop in fuel-related emissions, such as carbon dioxide and sulphur dioxide – of approximately 27 per cent per unit of time, or 19 per cent per unit of distance. In reality, the emissions reductions will be higher than 19 per cent, as ships sail only a part of their time at their optimal speed.

If you slow ships down you need more ships to move the same amount of cargo in a given time and this has been one of the arguments used against reducing the speed of ships. However, the study shows that for the most important fleet segments – tankers, bulk carriers and container ships – the recent economic downturn has resulted in sufficient overcapacity in the fleet to cut emissions by around 30 per cent by slow steaming. Moreover, the study assumes levels of speed reduction that are consistent with the safe and reliable operation of ship engines and that do not require the retrofitting of new equipment.

The overcapacity in the world fleet can be addressed in several ways. One is to decrease the amount of cargo carried per ship, another is to idle ships, and a third is to sail at lower speeds. The latter option has the advantage that fuel is saved and emissions are reduced.

“In short, this study shows that the current overcapacity in the fleet presents the global shipping industry with a golden opportunity to make substantial reductions in emissions in the short term,” said John Maggs, Policy Advisor with Seas At Risk, “This is particularly important given the urgent need to peak greenhouse gas emissions in the next few years if global warming is to be kept well below two degrees and catastrophic consequences avoided.”

Consequently, speed reduction is an important part of the package of measures that will be necessary if the shipping industry is to make a proper contribution to the very large cuts in emissions that are necessary to avoid runaway climate change.

The launch of the study coincides with ongoing deliberations in the International Maritime Organisation (IMO) concerning the technical, operational and market-based approaches to tackle GHG emissions from shipping.

Christer Ågren

[1] The study, entitled “Going Slow to Reduce Emissions” was commissioned by Seas At Risk, undertaken by the Dutch consultancy C.E. Delft. Available from www.seas-at-risk.org.