But progress to reduce vessel speed is a happening far too slowly despite multiple environmental benefits

There is no doubt that technical progress will, or at least should, contribute providing practical solutions to challenges we face as society. This is certainly also applicable to address the two main urgent crisis the planet face: global warming and biodiversity loss. But at the same time we know that technical progress alone won’t be enough the fix those crisis nor will it act as the only solution. Thus, in context to both referenced crises, we need to think broader and practical. And often, progressive and very effective measures are just right in front of us and are far easier to implement than you might have expected.

Especially when it comes shipping. By transferring the vast majority of internationally traded goods from A to B, it is implicit that the shipping sector does leave a certain ecological footprint. Burning fossil fuels for propulsion resulting in air pollutants and GHG emissions; the cavitation created by the propellor resulting in severe ocean noise pollution; navigating right through breeding or feeding grounds of large megafauna resulting in collisions that most of the times end deadly to the animal hit; one could continue the list.

Technical measures alone won’t be enough

As long as the list, you will find a number of potential measures of what can be done to address each of the single aspects resulting in a kind of ecological footprint. For sure, many of such measures will be of technical nature, relate to the functioning of propellers, ship design, type of paint, zero emission fuels, you name it. But what about if there is one practical measure you could impose today which lowers the ecological footprint per se at almost no economic cost? And yes, it’s there: reducing vessel speed is such a measure which generates multiple environmental benefits. You may call it “slow steaming”.

The positive effects of slow steaming have been demonstrated many times and even widely applied for several years as a consequence of the world economic crisis in 2008. The third study by the International Maritime Organization (IMO) on GHG emissions summarizes that “Fleet activity during the period 2007–2012 demonstrates widespread adoption of slow steaming. The average reduction in at-sea speed relative to design speed was 12% and the average reduction in daily fuel consumption was 27%. Many ship-type and -size categories exceeded this average. Reductions in daily fuel consumption in some oil tanker size categories was approximately 50% and some container-ship size categories reduced energy use by more than 70%.” But after leaving that crisis behind, the industry was quick to speed up again and so sonification of the ocean continued to increase almost on global scale with e.g. the ocean noise emissions in European waters doubling between 2014 and 2019.

New study demonstrates that slowing down reduces ocean noise pollution

A new scientific paper published often provides the opportunity to give attention to a certain phenomenon. So here is one from January 2023. The scientific paper “Large-Scale Simulation of a Shipping Speed Limitation Measure in the Western Mediterranean Sea: Effects on Underwater Noise” by a group of French scientists concludes that speed limitation is an effective mitigation measure to reduce underwater shipping noise. The most significant effect was demonstrated with a reduction of speed to 10 knots in deep-water environments.

That sounds like very good news. But there is another aspect which puts these findings in a positive light. The area of the scientific simulation – the North-Western Mediterranean Sea – is actually part of an area which four countries – France, Italy, Monaco and Spain – have proposed to become designated as a Particularly Sensitive Sea Area (PSSA). The proposal has already been accepted in principle but awaits formal adoption at the next meeting of the Environmental Committee (MEPC) of the IMO which will take place in July 2023. The so-called PSSA has one clear objective: to reduce risk of ship collisions with endangered fin whales and sperm whales inhabiting that area which, to a large extent, had already been identified as an Important Marine Mammal Area (IMMA).

Being hit by a vessel poses the main single threat to these two species in that area. But unlike in some other areas, the science about the distribution and habitat use of these large marine mammals does not result in clear guidance for where shipping routes would reduce the risk of colliding with whales, but only one other method has yet been proven to reduce such collision risk: slowing down! Reducing vessel speed to around 10 knots would be the most effective way forward preventing endangered animals being deadly hit and, as we have just learnt, also result in measurable reduction of ocean noise pollution, another threat these animals, but also other marine wildlife, face.

International shipping company announces slowing down and re-route to protect whales

And there is more good news. Almost at the same time of the release of the referenced scientific findings, STOLT-NIELSEN, the world’s largest operator in chemical tankers, released a statement confirming to slow down vessel speeds in three regions and change their navigation route in another. The decision has been made after a consultation process towards implementing measures to reduce the risk of colliding with endangered whales.

In more detail, the measures taken are:

  • re-routing 15 nautical miles south of the current traffic lane off southern Sri Lanka to avoid collisions with blue whales;
  • slowing down vessel speed by 20% from 12.5 to 10 knots in the north-west Mediterranean Sea for fin and sperm whales: in the waters around Vancouver Island, for orcas; and on the east coast of the US for North Atlantic right whales and humpback whales.

Noteworthy, the company acknowledges the fact that slowing down their vessels will also reduce ocean noise emissions and help achieve the UN Sustainable Development Goal 14 – Life below water.

But even with such large player taking action, one might wonder: why aren’t others, and why is it so difficult to get governments to agree within the core UN body regulating shipping – the International Maritime Organisation. It is also worth asking why the set of actions proposed by the four countries alongside the designation of a large area in the Northwestern Mediterranean Sea as PSSA does not include the only effective measure scientifically proven: a mandatory speed limit, or even a certain reduction in speed per vessel category.

Creating a level playing field – a way forward

Measures of voluntary nature are – as the current situation proves – simply not resulting in the expected or needed result. Only the adoption of a mandatory vessel speed reduction throughout the area would effectively reduce the collision risk to large whales while creating a level playing field for all shipping companies. It would certainly prevent economic disadvantages for especially those companies which are willing to reduce their ecological footprint by themselves.

No one would dispute the fact that slowing down vessels results in multiple environmental benefits. Among the various operational measures available, speed reduction has been shown to be the most cost-effective way to reduce the environmental impact of shipping, enabling emissions of greenhouse gases and air pollutants such as sulphur oxides (SOx), nitrogen oxides (NOx) and black carbon, as well as underwater noise, to be reduced very significantly and with immediate effect.

So, if not for the sake of whales or the wider marine ecosystem, what about for the sake of human health? Or for combating climate change that threatens our very existence?

Let’s put it that way: there is an urgent need to reduce GHG emissions from shipping – a sector with more than 1 billion tonnes of GHG emissions per year globally and currently the biggest world’s laggard in its decarbonisation process – and one effective measure which could be put into practice today. Your assumption is correct: slowing down.


Nicolas Entrup
Director International Relations


Carlos Bravo
Ocean Policy Expert