Podcast Episode 1.54

The bottom line on sustainable shipping: Can the shipping industry reach zero emissions?

with Bryan Comer, Marine Program Lead at the International Council on Clean Transportation

If the international shipping sector were a country, it would be the sixth largest CO2 emitting nation in the world. Every year, 11 billion tons of goods – about 80% of all the goods we use or consume – reach us by ship, emitting nearly a billion tons of CO2 into the atmosphere in the process. And, about 40% of those goods – nearly 4.5 billion tons – are fossil fuels.

Unlike switching to renewable energy and electric road vehicles, there is not an obvious short-term economic benefit to decarbonizing shipping, which makes even the simplest solutions (like slowing down the ships!) difficult to incentivize. Climate Now sat down with Bryan Comer, Marine Program Lead at The International Council on Clean Transportation (ICCT), to discuss the shipping industry’s decarbonization goals, the policy changes needed to reach them, and the future of sustainable shipping. 


Bryan Comer
Marine Program Lead at the International Council on Clean Transportation


Bryan Comer

Marine Program Lead at the International Council on Clean Transportation

Bryan is a lead author of the Fourth International Maritime Organization Greenhouse Gas Study and is an expert on Arctic shipping issues, including efforts to reduce black carbon emissions and the use of heavy fuel oil. Bryan’s work highlights how maritime transportation can transition away from fossil-fueled ships to zero emission vessels.

Hosted By:

James Lawler
Climate Now Host


James Lawler

Climate Now Host
James Lawler is the founder of Climate Now. James started Climate Now as a way to learn about climate change and our energy system. Climate Now’s mission is to distill and communicate the science of our changing climate, the technologies that could help us avoid a climate crisis, and the economic and policy pathways to achieve net zero emissions globally. James is also the founder of Osmosis Films, a creative studio.


[00:00:00] James Lawler: I’m James Lawler and you are listening to Climate Now. Today, I’m joined again by our guest host, Darren Hau, senior charging manager at Cruise and former applications engineer at Tesla. This is the second installment of our series on decarbonizing marine transportation. The aim of today’s episode is to get a sense of the landscape when it comes to decarbonizing shipping.

[00:00:28] James Lawler: What are options to reduce emissions, what are the barriers, and who are the entities that will decide and regulate how it is done?

[00:00:34] Darren Hau: That’s right, James. For most of us, the ins and outs of the shipping industry, and why this is such a challenging sector for us to decarbonize, is not as easy for us to grasp as, say, driving or the airline industry. Luckily, we are speaking today with Dr. Bryan Comer, who leads the marine program at the International Council on Clean Transportation (ICCT). Bryan’s been researching how to assess and reduce emissions coming from marine transportation for more than a decade. 

[00:01:01] James Lawler: Bryan, welcome. I’d love to start with a little introduction to what the ICCT is. Can you explain to us the role of your organization and the kind of work that you do there? 

[00:01:10] Bryan Comer: Yeah. The ICCT is the International Council on Clean Transportation. We’re a nonprofit research organization. In role at the ICCT, I actually go and advise environmental non-governmental organization NGO delegations at the International Maritime Organization (IMO), which makes the policy for international shipping. So, you have the opportunity here to do everything from research design, to doing the work, to interpreting what it means for policy, and then explain it to the policymakers themselves on exactly what your research findings can help them do. 

[00:01:52] Darren Hau: Out of curiosity, what is the makeup of the staff at the ICCT?

[00:01:57] Bryan Comer: Mostly it’s engineers, and quite a few PhDs, although myself and my staff were more on the technical policy analysis side, so we have degrees in public policy. I have a marine biologist on staff, which is kind of cool. 

[00:02:13] Darren Hau: That’s really cool that you guys have that cross-pollination going. I really want to ask what that marine biologist does on your team.

[00:02:19] Bryan Comer: Well, she has been analyzing the distribution of wash water discharges from ships that use scrubbers. So, the scrubbers suck up seawater and they spray it into the exhaust, and the seawater is basic and the exhaust is acidic. The idea is that you’re removing sulfur from the exhaust to meet fuel quality standards for sulfur, so instead of removing the sulfur from the fuel, which would make the fuel more expensive, you just remove it from the exhaust. It ends up being cheaper, but then you’re collecting oil and carcinogens and acids and particulate matter and dumping it into the ocean. So, she’s been modeling out where the ships discharge that wash water and linking that to impacts on marine life. 

[00:03:13] Darren Hau: I’d love to dive into our next question. Could you give us a brief overview of the shipping industry in general? For example, how much stuff is shipped versus manufactured locally, you know, maybe shipping versus freight versus rail or air?

[00:03:27] Bryan Comer: Sure. So, the shipping industry moves about 11 billion tons of stuff around the world each year, that’s about 300 times more than what you move by aircraft, for instance, and those are the two main international freight transportation modes for getting across an ocean, at least. To move 11 billion tons of cargo, ships are emitting about a billion tons of carbon dioxide. If it were a country, the shipping sector would rank sixth, more than Germany.

[00:04:10] Darren Hau: To put those 11 billion times in context, what percentage is that globally? 

[00:04:16] Bryan Comer: Let’s see. About 80 percent of total freight transportation by mass is carried by ship. A lot of people say 90 percent, it’s actually more like 80 percent.

[00:04:30] Bryan Comer: That’s about 70 percent by value. 

[00:04:33] Darren Hau: Gotcha. Thanks for that context there. We’re obviously not shipping experts, so can you enlighten us on the types of ships there are, what they transport, and then maybe how shipping emissions are distributed among those different types of carriers?

[00:04:48] Bryan Comer: In my team, we like to say that there’s the big three, and those are container ships, bulk carriers, and oil tankers. Those three ships account for over half of the emissions from the sector.

[00:05:02] Bryan Comer: There’s about 50 to 60,000 commercial ships that are big enough to really count. In total around the world, there’s hundreds of thousands of ships, but you have to sort of draw the line. So, of those 50 to 60,000 ships, 5,000 are container ships, so about 10 percent of the fleet, and they’re responsible for about 25 percent of carbon dioxide emissions from the sector.

[00:05:32] Bryan Comer: Then we have bulk carriers. There’s about 10,000 of those, and they are responsible for about a fifth of emissions, and then oil tankers for about a sixth of emissions. So, the container ships are moving manufactured goods back and forth, you know, if you look around your office and look at all the stuff you have, quite a bit of it, maybe all of it was moved at some point on a ship.

[00:06:01] Bryan Comer: But the other portion of the shipping industry that maybe doesn’t get as much attention is just how much fossil fuels are transported by ships. So, we have bulk carriers and oil tankers, and those two are transporting coal and crude oil and petroleum products, diesel fuel, and about 40 percent of that 11 billion tons of cargo is fossil fuels.

[00:06:30] James Lawler: Wow, so 40% of the cargo we are moving around in these carriers and tankers are fossil fuels. So, just reducing our dependence on fossil fuels in all other sectors would have a huge impact on reducing shipping emissions. But, let’s get into some specifics. What are the actual goals for emissions reduction in the shipping industry itself?

[00:06:49] Bryan Comer: So, the shipping industry is regulated by the International Maritime Organization. It’s a specialized agency of the United Nations, and it’s designed such that countries that are interested in shipping, which is almost every country on Earth, come together and put together proposals on how to regulate ships for safety and for the environment.

[00:07:15] Bryan Comer: So, the International Maritime Organization, in 2018, we agreed to a couple of targets. The first is that by 2050 absolute emissions from the, sector would fall at least 50% from 2008, which was the historic peak in shipping emissions just before the global financial crisis. 

[00:07:35] Bryan Comer: By 2030, we would reduce the carbon intensity of shipping. So, how much carbon dioxide or greenhouse gases, are emitted per ton per nautical mile by at least 40% compared to the 2008 baseline. 

[00:07:53] Bryan Comer: And that we would work to eliminate greenhouse gases from the sector as soon as possible, before the end of the century, and that we would try and align the strategy with the Paris Agreement temperature goals. Maybe more than try. The vision of the strategy is to be aligned with the Paris Agreement temperature goals.

[00:08:16] Bryan Comer: So, you may intuit that a 50% reduction by 2050 is probably not aligned with the Paris Agreement temperature goals. Part of the initial strategy is that it’s reviewed and updated every five years. So, in 2023, next year, we’re going to have the first revision of the greenhouse gas strategy and the United States, under the Biden Administration, has put forward a proposal with other countries to achieve zero emissions by 2050, not even net-zero. Literally, zero emissions from the sector by 2050. Other countries have come on board with proposals for net-zero by 2050, recognizing that you might need to use sustainable biofuels or synthetic fuels made with renewable electricity that have negative upstream emissions when you produce them, and positive downstream emissions when you burn them, in the ship.

[00:09:17] Bryan Comer: So, the actual targets for the sector are expected to really strengthen next year, but there’s a big mismatch between ambition and the regulations that the International Maritime Organization is developing to try and achieve those targets. 

[00:09:33] James Lawler: What are the actual strategies that are proposed in that target? What is the path to get from where we are to zero emissions by 2050? 

[00:09:44] Bryan Comer: At the International Maritime Organization, usually the debate goes like this. What’s the target? Let’s negotiate that, what numbers sound good, what years sound good, from what baseline? Then, how are we going to achieve this?

[00:10:01] Bryan Comer: But the negotiation starts first on what are the targets? And then, how do we get there? 

[00:10:07] Darren Hau: Is it just a finger in the air? This target sounds good, or like, how does that initial stake in the ground get set? 

[00:10:12] Bryan Comer: My group tries to explain, if you’re trying to be aligned with the Paris Agreement, what’s the emissions reduction trajectory that you need to be on in order to have a carbon budget by 2050 that could be consistent with the Paris Agreement temperature goals. Basically, how much carbon budget do we have between now and before we exceed 1.5 or two degrees. And then, what does that imply for how quickly we need to reduce emissions from the sector.

[00:10:44] Bryan Comer: In addition to that trajectory, we model out how much can you achieve just by operational measures? The easiest thing to do is to slow a ship down. There’s a cubic relationship between how fast you go and how much fuel you consume.

[00:11:02] Bryan Comer: So, in order to go just a little bit faster, you have to consume a lot more fuel, and the opposite is also true. If you go a little slower, you consume a lot less fuel, even though it’ll take you a little longer to complete your journey because it’s a cubic relationship, you end up saving fuel. That’s the easiest thing to do.

[00:11:20] James Lawler: I’d love to ask you a question about that that James Womack and Daniel Jones described the creation of a tin can in their book, Lean Thinking. First, you have bauxite, which is the raw ore from aluminum, which is mined in Australia. That is reduced in a chemical reaction and shipped as aluminum oxide to Sweden or Norway from Australia. In Sweden or Norway, it sits in a yard sometimes for several months before it’s processed into aluminum ingots, which are then shipped to Germany, where it sits for a number of weeks before it’s rolled and flattened, and then sent to England where the cans are actually made. 

[00:12:01] James Lawler: So, at each step, you’ve got huge amounts of emissions that are released from the heat required for that step of the transformation, and at each step, you have transportation punctuated by a lot of waiting around. It’s a great case study for just how inefficient the whole system ends up being, and I’m wondering if that, you know, resonates with, with the work you’ve done. 

[00:12:21] Bryan Comer: It does. That is one interesting challenge of the international shipping industry, is how do you make sure that the ships that are arriving at ports are doing so at a time that makes sense to reduce congestion, to make sure ships aren’t just idling off the coast, which is a big problem that we’ve had during the pandemic off the west coast with container ships, and with oil tankers as well. But there’s not a global logistics, a plan to make sure that all the ships are operating and in harmony across the seas.

[00:12:55] Bryan Comer: And so, slowing the ship down could reduce congestion because you would have more time to figure out when the ship ought to be calling up the port, and also it could be a lot more efficient. There’s likely some interaction here between the speed at which the goods need to get there and how the ship is rented out.

[00:13:21] Bryan Comer: The bulk carriers in the oil tankers are rented out, so they’re chartered is how we would call it. And so, whoever’s renting the ship tells the ship when it needs to leave one port and when it needs to arrive in the other port, and then the captain of the ship is in charge of figuring out what speed they should sail to get there.

[00:13:43] Bryan Comer: You don’t want to miss that window. There’s fines associated with that in the charter agreement, so there is also this ‘hurry up and wait’ that can happen in the industry because of how the charter agreements are working out. 

[00:13:59] Darren Hau: I’d love to ask some other questions around what makes it difficult to accomplish these goals that you mentioned, right? Are there nuances that most people don’t think about that make it difficult to say one thing, but actually achieve that goal in the maritime industry? 

[00:14:12] Bryan Comer: There are a couple of challenges. One is on the policy side and the other is on the economic side. The only way we’re going to reduce emissions from the shipping sector is either if we make regulations that mandate ships do something different than they are currently doing, or if it’s less expensive to do the right thing.

[00:14:36] Bryan Comer: On the policy side, the International Maritime Organization usually ends up with regulations that are the lowest common denominator, because they’re trying to work under consensus, not necessarily unanimity. You’ll have countries that are quite ambitious, and you’ll have countries that want to maintain the status quo or even move backwards, and you end up with a regulation somewhere in the middle that usually is only an incremental improvement on where the industry was headed already. That needs to change if we’re going to achieve zero emissions by 2050, for sure. 

[00:15:15] Bryan Comer: That’s one challenge. The other challenge is it’s a global industry and competition can be fierce. Whoever is offering the cheapest way to move whatever you’re trying to ship from point A to point B, that’s who wins. I mean, the cheapest option now to run a ship is to flag in a country that isn’t going to charge you any extra taxes, is going to have lax, environmental, safety, and labor standards, and is going to allow the ship to use the cheapest fossil fuel.

[00:15:46] Bryan Comer: In fact, we have a situation now where, in 2020, the fuel sulfur limit for marine fuels reduced from a maximum of 3.5 percent to 0.5 percent, and that was supposed to have this shift to more expensive fuel, which would encourage ships to slow down and reduce their emissions, but what ended up happening instead is that a lot of ships installed sulfur scrubbers.

[00:16:13] Bryan Comer: That way they could keep using the cheapest high sulfur fuel and keep their freight rates low. So, the economics is really a challenge until the alternative fuels are less expensive than the fossil fuels, nothing’s going to happen on the market side. We’re working from a market angle and from a regulatory angle all at the same time and trying to pull enough levers on both of those sides to make sure that we actually do start reducing emissions from the sector. So far, between 2012 and 2018, we saw a 10% increase in emissions, so we’re going the wrong way. 

[00:16:55] Darren Hau: Got it. Well, this is a great segue to start talking about solutions that you’ve seen. Could you tell us about the trends in shipping decarbonization? What are some of the technologies or leaders in the space? 

[00:17:06] Bryan Comer: Sure. So, there’s a lot that we can do on the operational side, which I mentioned earlier, including just slowing ships down, but in order to get to zero emissions, we need to change the way that ships are fueled. That’s requiring a change not only in the type of fuel that’s used onboard ships, but also the type of propulsion system that we have onboard the ships. 

[00:17:32] Darren Hau: Could you walk us through what those different options are in making those changes?

[00:17:36] Bryan Comer: Right. When we’re thinking about the fuels that could be used to power international shipping, you need something that has a good energy density and that’s not too difficult to handle, and that you can use either in an internal combustion engine, or maybe a fuel cell. If we start with maybe the hardest situation, which would be a liquid hydrogen fuel in combination with a fuel cell, that requires having very insulated tanks, very cold fuel, and running it in a fuel cell which hasn’t been tested at scale yet for international shipping. 

[00:18:16] Bryan Comer: It gets easier from there. If you go to ammonia, which you can use in an internal combustion engine, that is easy to be liquified. It’s a gas, but if you apply just a little bit of pressure, it’ll liquefy, or if you cool it down just a little bit, it’ll liquefy. So, it might as well be a liquid. But burning it, you’re going to produce nitrous oxide N2O emissions, and that’s a greenhouse gas with a global warming potential almost 300 times as strong as carbon dioxide. We don’t know how much will be emitted by burning ammonia in a marine engine, so it’s not going to be zero greenhouse gas, like using hydrogen in a fuel cell would be. 

[00:18:59] Bryan Comer: Then we’re talking about methanol. Methanol is a liquid at room temperature and pressure. That’s good, we can store it onboard the ship. It’s got about half the energy density of fossil fuels, so you need twice as much of it if you’re going to go the same distance, but the same is true for ammonia as well. It is a hydrocarbon fuel, so when you burn it, you’re going to produce carbon dioxide. The source of the carbon is really critical when you’re using methanol as a decarbonization strategy. 

[00:19:35] Bryan Comer: We have biofuels and we have synthetic fuels as our options. There are huge concerns on the sustainability of biofuels because many of them are made with corn or soybeans, and those have direct and indirect land use change consequences that can make them worse than the fossil fuels they’re replacing. If it’s from a sustainable biosource, like some of that would have become a waste material, then that’s good, but the supply of that is really limited.

[00:20:09] Bryan Comer: If it’s from direct air capture of carbon dioxide, that’s good. You can call that net-zero carbon dioxide, but that’s where the challenges of cost and scaling up, come into play. But we are seeing companies like Maersk, who have been the leader on the container shipping side, and really for the international shipping sector in total, starting to invest in companies that actually produce green methanol. They’re being transparent, or they intend to be transparent at least, about what the source of the carbon dioxide is and how they’re doing the conversion. 

[00:20:51] Bryan Comer: We’re looking to hold them to account on that and make sure that they’re transparent. 

[00:20:54] James Lawler: So, Bryan, I noticed you didn’t include liquified natural gas or LNG on your list of options, even though I understand it’s being touted as a way to quickly decrease shipping emissions. Can you comment on why it didn’t make the list?

[00:21:06] Bryan Comer: No, we actually didn’t talk about LNG at all, which is one of my hobby horses on why it’s not a climate solution for ships, and yet half of cruise ship capacity that’s being built today, and I think a third of container ships and maybe a quarter of bulk carriers and oil tankers are designed to run on LNG, which is methane, and burned in engines that are leaking large amounts of unburned methane to the atmosphere.

[00:21:35] Bryan Comer: We’re actually just launching a study. We launched it a couple of days ago, FUMES, Fugitive Methane Emissions from Ships, where we’re partnering with a company that flies drones and helicopters, and another research organization that goes on board ships to actually measure methane emissions from LNG fueled ships, to try and better understand the greenhouse gas consequences of using this fuel that has lower carbon dioxide emissions, but higher total greenhouse gas emissions in most cases. 

[00:22:09] Darren Hau: That’s a good point. That all of these fossil fuel alternatives might reduce CO2 emissions, but they come with other risks. For example, I know with the ammonia, one of the big challenges is the safety of this toxic material. Maybe you could speak to that a little bit more? And on the methanol side, correct me if I’m wrong, but I’ve heard that methanol can actually corrode steel, and that will make it more difficult to adapt traditional containers and pipes to handle that fuel.

[00:22:33] Bryan Comer: Methanol is already transported by ship, and so there’s actually been a lot of work done ensuring that the methanol can be safely handled on board ships and it was just approved, I think it was last year, as a ship fuel. On the safety side, IMO is actually pretty competent on that, so that I’m not too worried about. It is toxic though, you don’t want to ingest it, but it’s not a breathing hazard like ammonia is. So, if there’s even a small ammonia leak, then the entire crew could be killed. If there’s a spill, then the marine life would be killed as well that’s around the ship. 

[00:23:14] Darren Hau: Your biologist would not be very happy with that.

[00:23:17] Bryan Comer: Yes, our marine biologist would not be happy with that. So, that’s a big challenge. Methanol, if it’s spilled, is biodegradable, but you know, there’s some acute toxic impacts as well during the initial part.

[00:23:29] Bryan Comer: So, I mean, there’s tradeoffs with all of this. I think the safest thing would be green hydrogen. Even that’s not risk-free because you have a fire and explosion hazard, but if you’re going to have a fuel onboard the ship, unless it’s wind power, then all of it needs to burn. That has the advantage of not being toxic, not being poisonous, and not being a greenhouse gas.

[00:23:56] Darren Hau: Let’s talk about hydrogen to wrap this up, because one of your papers mentioned that you studied a transpacific corridor route, and you found that 99 percent of those voyages could actually be powered by cryogenic liquid hydrogen and not really affect the fuel capacity or operations very much.

[00:24:15] Darren Hau: Can you maybe speak a little bit more to that? Why are we not hearing more discussion of cryogenic, hydrogen and fuel cells in that case?

[00:24:23] Bryan Comer: We modeled out the transpacific container ship corridor, and we looked to see if you could complete those voyages using liquid hydrogen fuel, which is cryogenic, by fitting it within the same space as the existing fuel tanks and the engine systems, and not changing the speed of the ship or anything like that. Half of the voyages could be achieved just as they normally were, you didn’t have to change anything about it. The other half, you would need to add an additional refueling stop to complete the voyages. In that case, you could achieve 99 percent. The other way to achieve it is, you replace some of your cargo space with fuel, but it’s not necessary if you have that additional refueling stop. 

[00:25:09] Bryan Comer: We’ve also modeled out pairing hydrogen fueled ships with wind assisted propulsion, which reduces how much fuel you need to consume because you get power from the rotor sails in this case is what we modeled.

[00:25:24] Darren Hau: Gotcha. So, I was probably being a little optimistic in saying barely any changes. There would have to be refueling stops, or minor changes to cargo capacity. 

[00:25:32] Bryan Comer: The one thing that we didn’t model out though is, what if you slowed down the ship a little bit. In that case, almost certainly you would be able to achieve all of the routes with a reduction in speed, but we wanted to do a pretty tough scenario because we knew that everything else would be easier.

[00:25:49] James Lawler: Have you ever done an analysis of what would happen if you pulled all the levers, or looked at which of these strategies will have the biggest and fastest impact and where we should be concentrating our efforts? Because it strikes me from our conversation that slowing down is going to give us the biggest bang for our buck. 

[00:26:04] Bryan Comer: We’ve definitely modeled out how exactly you could get to zero emissions on a trajectory that could be consistent with the Paris Agreement temperature goals, and it requires slowing down as the first step, and then it requires scaling up the low and zero lifecycle greenhouse gas fuels pretty rapidly. That would require reducing all of the political and economic barriers to progress.

[00:26:34] Bryan Comer: So, it’s certainly possible. It’s definitely possible. The challenge here is going to be to do it in good time, and make sure that we have rules that are in place that force the transition to occur. Not just things that rely on the market to incentivize the change, we need a combination, not only of the market-based measures, but also command and control.

[00:26:57] James Lawler: Well, Bryan, thank you so much for your time today. This has been really fascinating, and we’ve covered, you know, it’s a great primer, really, for anyone who’s interested in this space.

[00:27:06] Darren Hau: Thanks for joining us, Brian. This was really fascinating. 

[00:27:09] Bryan Comer: My pleasure. Thanks for having me and thanks for your interest in our work.

[00:27:16] James Lawler: That’s all for this episode of the podcast. Climate Now is made possible in part by our science partners like the Livermore Lab Foundation. The Livermore Lab Foundation supports climate research and carbon cleanup initiatives at the Lawrence Livermore National Lab, which is a Department of Energy Applied Science and Research Facility.

[00:27:33] James Lawler: More information on the foundation’s climate work can be found at livermorelabfoundation.org. To listen to other interviews from Climate Now, watch our videos, read our articles, or sign up for our newsletter, visit climatenow.com. If you’d like to get in touch, you can email us at contact@climatenow.com or tweet us @weareclimatenow.

[00:27:51] James Lawler: We hope you’ll join us for our next conversation.

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