Toxic, filthy and cheap, the sludge-like substance known as heavy fuel oil has powered the shipping industry since the 1960s. What is perhaps less well known is that this same substance is still used to power more than half of cruise ships today, making what many choose as an alternative to flying one of the most environmentally damaging ways to travel.
The good news is that the industry, under pressure from environmentalists and new regulations, is adopting new technologies, energy saving designs and studying alternative fuels.
But can cruises, especially at the rate the market is growing, ever be considered a “sustainable” way to travel? And, with a target date of net zero by 2050, are they decarbonising fast enough?
How green is my cruise holiday?
While the cruise sector forms a tiny part – just 2% – of the shipping industry, the ships are growing in size and number. As a result, they need to do more than they are doing now towards sustainability, says Inesa Ulichina, sustainable shipping officer at Transport & Environment (T&E) campaign group.
“Part of the reason we focus on cruise ships is because they are close to people,” she says. “Cruise ships spend, proportionately, more time in port than other ships, particularly in pristine and natural locations where the impact of pollution is greater.”
Critics say the cruising boom – ships have soared in number from 21 in the 1970s to 515 today and the world’s biggest have doubled in size since 2000 – dwarfs decarbonisation efforts by individual lines and vessels. A study commissioned by the high level panel for a sustainable ocean economy concluded that the 2% annual improvements in carbon intensity reported by two leading cruise lines in recent years is “cancelled out many times over” by an expected 6% to 7% rise in passenger traffic.
“If we look at Europe, the worst emitting ships are cruise ships or large ferries,” says Ulichina.
A list of Europe’s top 20 worst carbon emitters, compiled by T&E from data required by EU laws for ships to report carbon dioxide emissions, featured nine of the largest cruise liners, 10 ferries and just one cargo vessel.
Up to 40% of the total energy consumption of a cruise ship is the “hotel operations” – swimming pools, spas, lounges and restaurants – on board, according to Sintef, a European research organisation.
It is unsurprising then, that cruise ships pumped out 17% more carbon dioxide in 2022 than they did in 2019, according to a T&E study, while methane emissions rose 500% over the same period.
So should I choose a ship powered by a different type of fuel?
Earlier this year, Icon of the Seas, a 20-deck, 7,600-passenger, theme-park rich party-ship, longer than the Eiffel Tower is tall, drew crowds when it launched in Miami. It runs on liquefied natural gas (LNG), which its owner, Royal Caribbean, describes as the “cleanest burning marine fuel available”. Another similarly sized vessel, Star of the Seas, will follow in 2025 and a third in 2027 – all powered by LNG.
Only 19 ships, or 6.7% of the fleet are powered by LNG, says the Cruise Lines International Association (Clia), which represents 90% of operators in the sector. By 2028, it will rise to 10%. More than 15% will be equipped with battery storage and 15% capable of running on methanol in the next five years, the first in 2025.
But environmentalists have warned that, while LNG, a fossil fuel, burns more cleanly than marine oil, there is a risk LNG-powered ships will leak methane, a powerful greenhouse gas, into the air. Bryan Comer, director of the International Council on Clean Transportation, a US thinktank, estimates that using LNG as a marine fuel emits 120% more life-cycle greenhouse gases than marine oil.
Marcie Keever, of Friends of the Earth US, says the industry has a history of adopting the “wrong” technology. When told in 2020 to reduce air sulphur emissions, many cruise lines instead adopted “scrubbers”. These are systems built into ships to clean exhaust gases – but they dump the chemicals removed from the exhaust directly into the sea instead.
“They [cruise operators] are talking about converting to other types of fuels but when they choose to use LNG, they are locking in climate-destroying technology,” says Keever. “Our opinion right now is just pause. Don’t adopt the next failing technology for the climate.”
Which cruise companies do best on sustainability?
While the larger vessels (greater than 10,000 gross tonnes) are the biggest contributors, producing 90% of the sector’s total greenhouse gas emissions, the leaders in decarbonisation tend to be companies with smaller vessels.
Hurtigruten, a Norway-based company that operates three small vessels with hybrid technology, aims to launch “SeaZero”, the first climate-emissions free, electric cruise ship in 2030.
“For expedition cruise ships, some of the companies, like Hurtigruten, are the ones investing in batteries and vessels that could be sustainable,” says Ulichina.
Hurtigruten’s goal of a climate neutral ship by 2030, has “a lot of dependencies” Gerry Larsson-Fedde, the company’s chief operating officer, acknowledges, such as whether or not the technology will be sufficiently mature. “We’ve gone for batteries because the technology is developing quickly, meaning you can get more and more energy stored in less and less space, with less weight.”
One of the biggest challenges is land-based infrastructure, he says. “You need a lot of electricity in charging areas and you need to charge quite quickly.”
Sönke Diesener, of German based NGO the Nature And Biodiversity Conservation Union, says battery capability is hugely dependent on the places a ship visits. “If they [Hurtigruten] sail in the Norwegian coast, they have infrastructure for reloading batteries. But for ships that sail to the Galápagos, or the Arctic, batteries would be too heavy.”
That is one reason cruise companies are focusing on alternative fuels for bigger ships.
There are companies looking to take things even further – though only for smaller, high-end vessels. French Polar company, Selar, aims to power the futuristic Captain Arctic, a 36-passenger polar expedition ship using sun, water and wind by 2026. The “almost zero emissions” ship design has 35m sails that retract like a Swiss army knife when not required.
How does the industry aim to mitigate its impact on the climate?
The Clia says its member cruise lines are investing in new ships and engines that “allow for fuel flexibility”. By this it means they have included capacity for renewable biodiesel, green methanol when available, and LNG. Data published by the International Maritime Organisation shows cruise lines have reduced their use of heavy fuel oil from 74% in 2019, to 57% today.
Ships operating on LNG will be able to switch to renewable “zero and near-zero fuels” such as bio or synthetic LNG when it becomes available at scale with little or no engine modification, says the Clia.
Half of all ships can connect to an onshore power supply, a 23% increase from 2023. This will rise to 76.5% by 2028. However, only 35 of the world’s ports (3% of the total) have a cruise berth with onshore power supply.
The EU is bringing in significant penalties for sailing on dirty fuel from next year, and has set targets for greenhouse gas reduction. The hope is that this kind of legislation, coupled with pressure from environmentalists and the public, could drive more positive changes for cruise ship holidays in the future.
