The scale of shipping's CO2 emissions

And some other unfortunate substances too...
30 January 2024

Interview with 

Peter Selway, Powercon & Lisa Lewis


A cruise Ship


If you’re a human being on planet Earth, the chances are you rely on shipping to uphold your day to day life. Some estimates put the amount of commerce transported worldwide by ships as high as 90%, that’s food, medicine, cars, pretty much anything you can think of. But all of that comes at a carbon cost. To find out more, here are a couple of people who can outline the scale of shipping’s carbon footprint...

Peter - So the shipping industry globally produces about 3% of greenhouse gases, but it's responsible for transporting 90% of the world's commerce. So it's extraordinarily critical to the world's economy.

Lisa - If shipping were a country, it would be the sixth largest emitter in the world.

Will - To jump on that point and to make sure that we're all on the same boat, as it were, it would be so much higher if we weren't using boats to transport stuff around.

Peter - Yes. So shipping is an extraordinarily efficient way of transporting, moving goods and people. On a short sea route, from Dover to Calais, a ship like this would emit about 16 grams of CO2 per tonne-kilometre, whereas road transport would use about 62 grams of CO2 per tonne-kilometre. So it's much more efficient and along the routes it becomes even more efficient still.

Lisa - If we remember that shipping is 3% of global emissions, road equates to approximately 15%, aviation is only 2.5% of global emissions, but the efficiency of using jet fuel is far less efficient than a ship engine.

Will - Given that this is still the best way of transporting all the world's goods, it is still the plan to reduce the amount of CO2 being produced. Is there a set amount for a set date?

Peter - The UK government has committed to decarbonising shipping by 2050. To be on track to hit that target, we need to reduce emissions by 15% between 2022 and 2030. And at the moment, unfortunately, we're not on track to do that.

Will - This is all talking about carbon dioxide. Is that the only greenhouse gas or harmful substance that is in play when we're talking about trying to reduce the footprint of shipping?

Lisa - No, absolutely not. Combustion isn't a hundred percent efficient. At its peak it's approximately 65% efficient for the main engines. Compare that to a petrol car which is 35% efficient. And when it's not a hundred percent efficient, you get waste products coming off. But if you're burning fossil fuels, you're going to get nitrous oxide, sulphur oxides, black carbon particulates, fugitive emissions, unburnt fuel gets leaked... there are lots of things that can damage the climate and human health.

Peter - Most ports are in town and city centres. Often when you see pictures of a ship, you might see some black carbon coming out of the chimney stack. What you can't see is the nitrous dioxide and the sulphur dioxides. The problem is, even with the low sulphur fuel that's being used at the moment, it has still got a hundred times the sulphur content of road diesel, and that pollution has generally been blown straight over these towns and city centres.

Will - This is almost a direct public health concern as well as a general climatic concern as well?

Peter - Absolutely. Shipping, by its nature, is out in the ocean and I think it gets forgotten about. Although it's a really efficient way of transporting goods and people, there are still big problems and there are big polluters. Particularly when that pollution is close to humans, the impact on human health is considerable.

Lisa - The modern experience of using a ferry or a cruise ship is very much more like a bubble than actual exposure and experiencing the maritime world. People drive on in a car, they go to very comfortable lounges, they use the restaurant, they might wander out for a quick walk on the deck on the prom, but often not at all on a short crossing between Dover and Calais. Therefore people are in some way disconnected and it's more of a sanitised journey.

Will - All of what you're saying to me right now makes this sound like a really multi-level, multifaceted problem to solve.

Lisa - So decarbonisation as an aspiration has got so many problems that will potentially create friction on the journey towards that target state. We've got disconnection in public policy, drivers towards human health and drivers towards decarbonisation are not necessarily always aligned. The technology, some of it's in proof of concept stage, there are multiple options on the table. For a ship designer, ship owner, ship operator, which way are you going to go? Depending on your investment, you could have a long time to get that payback in terms of performance change and you could be many years down the road in your design or construction when the public policy changes and then what will you do? In terms of all the potential solutions around the alternative fuels, there are many complexities and constraints around that, which Peter can go into more detail with.

Peter - These ships are some of the biggest machines humans have ever created, so the amount of energy they use is also absolutely huge. There's lots of alternative fuels I've been looking at. If you want to hit these 2050 decarbonization targets, there's lots of fuels like hydrogen, methanol, ammonia, they've all got lots of disadvantages. There's none of them that's an obvious alternative, and none that produce anything like the quantities we are going to need to fuel vessels of this sort of scale. One of the most obvious alternative fuels is electricity, and there's two elements of electrification of vessels. When a ship comes into a port, instead of running its diesel engines, it plugs into the electrical supply from the grid from the country, and uses that supply of electricity whilst at berth. That's called shore power. The other solution is, in addition to shore power, if we can provide enough electricity where batteries onboard the ships, like the ship we're on at the moment, can store that energy and use that energy for propulsion. Fundamentally, what we're trying to do here is decarbonise shipping by 2050 at the absolute latest. Yes, there are lots of alternative fuels. Yes, there are lots of issues with those, but we can't let that prevent us making the right measures now to try and decarbonise. One of the big challenges we have with the shipping industry is that a ship will last typically 30 years, whereas a car might last 10 years. Ships will still be in use in 2050, so we've got to decarbonise now and the only consensus fuel is electricity because all these ships are using electricity at the moment.


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