Cruises are among the most carbon-intensive ways to travel. They're also one of the fastest-growing tourism sectors — the number of passengers boarding cruises almost doubled in the past decade, peaking at 30 million in 2019. 

But cruise liners make up just a tiny fraction — less than 1% — of the ships crisscrossing the world's seas, which in total are responsible for around 2.5% of global greenhouse gas emissions. Despite their small share in international shipping, experts say cruise companies are uniquely positioned to drive emission-cutting innovations in the sector as a whole. Their huge profit margins, for example, mean they have the money to invest in alternative fuels and decarbonization technologies that could later be rolled out to larger ships. 

Lucienne Damm is the senior environment manager at TUI Cruises, a joint venture of the world's largest tourism operator TUI Group — which is based in Germany — and the world's second-largest cruise line Royal Caribbean. TUI Cruises employs more than 7,000 people and has seven ships operating on 80 routes around the world.

DW's environment podcast "On the Green Fence" spoke with Damm about how TUI Cruises plans to decarbonize its ships and meet its goal of reaching carbon neutrality by 2050.

DW: We're going to have to make big changes if we want to become carbon neutral by 2050. What are your reduction targets until then?

We want to bring down our relative emissions by 40% per passenger per overnight in 2025 compared to 2015. In 2030 we want to offer carbon neutral ships or routings. And hopefully we can have climate neutral cruising by 2050. However, we don't know yet which technology will be available in a larger scale by then, not only for the cruise industry, but also for the whole shipping sector and its hundreds of thousands of ships. We don't have one solution that fits all. It will be a mix of a lot of technologies. We know these technologies from shoreside applications, but we have to get them on to the ships. And that is one of the biggest challenges that people tend to forget. 

What does your fleet run on right now?

On marine diesel and heavy fuel oil with scrubbers and catalysts, so comparable to marine gas oil from the exhaust side. Heavy fuel oil was more or less erased with the International Maritime Organization 2020 regulation which stipulates that all the ships that don't have any exhaust gas treatment system have to use maximum 0.5% sulfur fuel or marine diesel oil (MDO).

But you have commissioned two liquefied natural gas (LNG) ships?

Yes, the first one will be delivered in 2024 and the second in 2026. We are now looking into options for how to fuel these ships, not with conventional LNG, but for example with bio LNG. We have a lot of proposals on the table and we now have to assess which makes sense ecologically and also economically. But LNG will be just an interim solution.

LNG only reduces CO2 emissions by up to 20% doesn't it?

That's a rather optimistic figure, actually. I think we have to bring these ships into service and really measure what the carbon reductions are. And also as soon as you use fracking gas, it's about way more than just emissions and it would destroy the whole purpose of sustainable shipping. There are some things are that are a "no-go" for TUI Cruises.

That's set in stone? No fracking gas on your ships?

For us it's not an option here. We still have to use some fossil LNG but hopefully we'll be able to replace it with some alternative bio LNG in a couple of years.

What about using batteries?

Everyone is talking about batteries and going electric. But it doesn't make sense on a seagoing cruise ship because these batteries would be too big and too heavy. The ship can't really manage that.

But isn't that what your competitor Hurtigruten is doing? Haven't they got a ship that's a hybrid electric ship?

Compared to our product, they are using much, much smaller ships on really defined routes in Norwegian fjords. You can see what regulation is doing there: Norway declared the Norwegian fjords as zero-emission areas as of 2026. So the pressure is on and a lot of companies are trying to find solutions, but mostly for these areas only. Hybrid-electric ships can maybe operate in the fjord, back and forth, but outside on the oceans they rely on the conventional engine configuration.

According to your last environment report from 2019, you seem to be doing a good job reducing food waste, reducing water consumption, reducing the per capita emissions. But  overall emissions are still growing because your operations are growing. So you're not really solving the global problem of rising CO2 levels?

On a fleet basis, of course, you have an advantage if you are bringing new ships into the fleet that are more efficient. With all the companies out there trying to tackle carbon emissions, you really have to look carefully into the relative and absolute carbon emission goals and you will see that most of them have relative targets. So the biggest challenge really is to have this absolute target for these absolute emission reductions. And we can only achieve that by switching fuels.

There's a lot of research happening regarding alternative fuels, but most are not scalable yet. Which fuel is going to come out on top?

It's a bit too early to say, but I think we have to push the biofuels because we still have so many conventional ships out there. With a good blend-in strategy, you can really cut your emissions and you can increase that drop-in amount from year to year, for example, and adjust to where you need to be by 2030 or in 2050.

And how are these biofuels to be sourced and scaled?

The sourcing issue is why the experts are a little bit reluctant here. I think we need to find solutions that source fuels from byproducts from shore-based industries. I think there's a lot of potential to use waste. And this also goes for cars or for aviation. For me, the bigger picture is that we have to find biofuels to use as drop-ins for the overall transportation sector.

How important is pricing in this context? Fossil fuels are, after all, still much cheaper than biofuels.

Yes, absolutely. It's difficult to make a prognosis at the moment but if the demand and also the production capacity of biofuels increase, we expect better pricing. But in general you are right, alternative fuels will be more expensive in the future and we have to take that into account. I think that companies have to be prepared to pay more for producing goods, but also to raise the asking price for the consumers.

Lucienne Damm is the senior environment manager at TUI Cruises.

This interview was conducted by Neil King and has been edited for clarity and length.