Are 'green' cruise ships good for the climate? (2024)

Many cruise companies are touting their green credentials. But can cruise ships ever be sustainable?

In January, the world's largest cruise ship set sail on its seven-day maiden voyage from the Port of Miami. The vessel, named Icon of the Seas, cost Royal Caribbean $2bn (£1.6bn) to build, has 18 decks, seven swimming pools and more than 40 restaurants, bars and lounges. It is 365m (1,195ft) long – 35m (115ft) longer than the Eiffel Tower and about five times as large as the Titanic.

The ship is powered by liquified natural gas (LNG) which Royal Caribbean has described as the "cleanest-burning marine fuel available". But environmental campaigners say LNG harms the climate because it leaks polluting methane into the atmosphere, which is about 80 times more potent than carbon dioxide (CO2) over a 20-year time span.

The industry's impact on the natural world is only set to grow as cruising booms. Ticket sales for cruise ships in 2024 have reached an all-time high. By the end of the year, 360 cruise ships are projected to have carried a total of 30 million passengers, a 9.2% increase compared to 2019, before Covid-19 hit.

"The problem is that the number of cruise ships keeps growing and the size of those cruise ships keeps growing as well," says Constance Dijkstra, shipping campaigner at the non-profit Transport & Environment. This will lead to more air and ocean pollution, she adds.

Cruise contamination

"We continue to caution people: 'If you're concerned about the environment, perhaps think about another kind of vacation,'" says Marcie Keever, director of the oceans and vessels programme at Friends of the Earth.

But is cruising worse than flying?

Cleaning up cruising

Port cities are starting to crack down on cruise ships amid mounting health and environmental concerns. In 2021, Venice banned cruise ships from entering its historic centre, restricting them to the industrial port in response to a request from UN cultural body Unesco due to cruise pollution damaging historic buildings. Amsterdam and Barcelona have also banned cruise ships from their centres, in a bid to curb pollution and reduce overtourism.

"This is an industry that's flown under the radar when it comes to regulation," says Keever. "We're now seeing communities stand up to cruise ships and say 'the environmental pollution and the amount of passengers you're bringing here is too much.'"

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But it's the need to switch away from polluting fossil fuels that arguably poses the industry's largest challenge.

"To have a green cruise implies a change of fuel, which is very difficult," says Dijkstra. "It's great that cruise ships are promoting recycling or going plastic free, but if they're going to keep using fossil fuels, we're in trouble."

Carnival Corporation, one of the world's largest cruise operators, is relying on LNG to reduce its carbon footprint. The company aims to reduce its carbon intensity – the quanity of CO2 emitted per nautical mile – by 20% by 2030, compared to 2019 levels. It currently has nine LNG ships in operation, with orders placed for four more.

"There's a limit to how far we can go with efficiency measures," Vice Admiral Bill Burke, chief maritime officer at Carnival Corporation, tells the BBC. "We're probably in a situation where we're only going to get 20-30% of our overall emissions reduction [through efficiency measures].

"Ultimately, we need new fuels and right now the best fuel out there, that is readily available, is LNG."

But others disagree that LNG is the solution to cruise ships' climate problem. "LNG is not a transition fuel," says Keever. "It shouldn't even be part of the conversation."

According to analysis by Transport & Environment, one of the UK's first LNG-powered cruise ships, P&O's Iona, emitted as much methane in 2022 as 10,500 cows over a year. A spokesperson for P&O told the BBC at the time that "LNG has much lower overall greenhouse gas emissions vs conventional fuels, even factoring in methane slip."

"Even with methane slip, the greenhouse gas footprint of LNG is better than marine fuel oil," says Burke. "It's the best fuel out there today."

Transport & Environment notes that no one knows the true extent of the methane emissions from LNG-powered ships, as the data is not available.

The race to replace gas

Whether or not LNG is an improvement on marine diesel, ultimately sustainable fuels that emit little to no greenhouse gases are needed to decarbonise shipping and meet the industry's 2050 net-zero goal, experts say. But which fuel can do this at scale remains up for debate.

Another alternative is green ammonia, made by electrolysing water with renewable electricity. Analysis by the Environmental Change Institute at the University of Oxford found that green ammonia, which emits no CO2 when burned but does produce nitrous oxide emissions, could decarbonise 60% of global shipping when provided at just the top 10 regional fuel ports.

But the Cruise Lines International Association (CLIA), the trade body for the cruise industry, says that alternative fuels such as methanol and ammonia are not viable options.

"There are currently no sustainable alternative fuels available at scale to achieve [the cruise industry's] decarbonisation ambitions," says Andy Harmer, managing director of CLIA UK and Ireland. "CLIA is calling on governments to help accelerate the transition by setting more ambitious production targets, particularly for synthetic and biofuels."

Burke says that while methanol is the fuel that people often talk about, it's more expensive [than LNG and marine fuel] and not readily available. "There is no green methanol today," he adds, noting that most methanol is currently produced using natural gas, rather than renewable energy.

The process to produce green methanol is complex: CO2 must be captured out of the atmosphere, via technology which is still emerging, expensive and as yet unproven at scale.

However, the other green fuels on offer also spark other concerns. Ammonia is a highly toxic, corrosive and flammable fuel, according to the Global Maritime Forum, a non-profit based in Denmark. "Ammonia is toxic," Burke says. "It's not the best fuel for cruises – we've got 8,000 people on our ships, and many in our engine rooms."

Dijkstra says many cruise companies say ammonia is unsafe to use on board ships carrying passengers. "But other companies are looking at that option…we are, for example, seeing DFDs ferries betting on ammonia," she says.

Keever says "it is feasible" for cruise ships to wean themselves off polluting fuels and switch to greener alternatives produced using renewable energy, such as methanol and ammonia, rather than fossil fuels.

"It's already happening in the larger shipping industry," says Keever, adding that Maersk, for example, is investing heavily in methanol. Transitioning to greener fuels "takes time and effort and a willingness to turn away from our dependence on fossil fuels," she adds.

Battery power

Norwegian cruise company Hurtigruten is focusing on a different technology to power its ships: batteries.

"We are using advanced battery and solar technology alongside old-fashioned tech: sails," says Hedda Felin, the company's chief executive. "We have sun 24 hours a day in the summer in Norway and it's very windy on the coast, so the ship is really tailored for the Norwegian coastline."

Four of Hurtigruten's fleet of nine cruise ships already have hybrid engines, which can run on both diesel and batteries.

"Hurtigruten are one of the leaders in the industry when it comes to adopting cleaner technologies, including [greener] fuels and advanced sewage treatment systems," says Keever. "And this is important because they go to places like the Arctic."

But there are limits to the distances batteries can power. The technology works well for Hurtigruten coastal cruises as "we are never more than six hours away from a port", says Felin. But it is not a practical solution for ocean cruise liners. "If we were crossing the Atlantic, batteries would definitely not be considered," says Felin.

Cruise companies visiting climate vulnerable locations, such as the Arctic, and bringing thousands of tourists to remote communities have a responsibility to operate more sustainably, says Felin.

"The cruise industry needs to take more responsibility…We are lagging behind massively," she says, adding that cruise companies have been slow to transition to cleaner alternatives.

But Felin says there is hope on the horizon; new technology and fuels will help power a more sustainable future for cruise ships. "There are several proven and safe choices for the future which mean we do not need to have fossil fuels on our cruise ships," she says. "That is the hope for the entire cruise industry."

The Royal Caribbean did not respond to the BBC's request for comment.

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