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Cruise Ships Face Headwinds Toward an Electric Future

The International Council on Clean Transportation (ICCT) says cruise travel is worse for the climate than flying. Here are some sustainable alternatives to reduce its impact

Even the most efficient cruise ships can emit more carbon dioxide per passenger-kilometer (pax-km) than an airliner.
July 30, 2022 | 09:57 am

Could electric mobility conquer the seas? That possibility is not crystal clear by now, but it seems there is a chance, albeit not for all vessels and not as a single solution to naval pollution.

The maritime industry releases more than 1 billion tons of carbon dioxide every year, 2.5% to 3% of the world’s total, according to the International Energy Agency (IEA). To curb these emissions, new fuel and energy sources are needed, and electricity, as it’s the case on land, is a promising alternative.

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This is especially relevant given that the International Maritime Organization (IMO), an agency of the United Nations, is committed to ensuring:

  • A minimum 40% reduction in carbon emissions from this industry by 2030 and a 70% reduction by 2050 as compared to 2008 levels.
  • A reduction of greenhouse gases (emissions of carbon dioxide, nitrous oxide, methane, and ozone, among others) by over 50% by 2050, as per the Paris Agreement.

While vessels such as pleasure boats or ferries already cover short distances powered by marine batteries, questions remain on the efficiency of e-engines in the case of large cruise ships sailing long-term and over long distances. The question is whether e-batteries are a realistic choice and what is needed for them to become a viable option.

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Experts at the International Council on Clean Transportation (ICCT) argue that tackling pollution in the seas, especially from cruise ships, is key. They estimate that traveling by cruise ship can be worse for the climate than flying.

How much do cruises pollute?

Methane leaks can make LNG-fueled ships more polluting than fuel oildfd

Traveling by ship can be a more affordable option for tourists visiting several destinations in a single trip compared to buying multiple plane tickets. According to the ICCT, their environmental impact is greater. This happens because even the most efficient cruise ships can emit more carbon dioxide per passenger-kilometer (pax-km) than an airliner.

A recent report by ICCT concludes that the largest and most efficient cruise ships emit about 250 g CO2 (pax-km), while the average carbon footprint of transatlantic aircraft ranges from about 10 g CO2 (pax-km) to 130 g CO2 (pax-km). This gap expands if we consider that cruise ships operate as floating hotels, so emissions from lodging should be added.

Research by Cornell University indicates that a one-night stay in a 4-star hotel in the U.S. may result in about 30kg of carbon dioxide emissions per room per night. If there are two people per room, the figure can be cut in half.

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Estimates by ICCT researcher Bryan Comer show that a person taking a 5-night trip logging 2,000 km on an efficient liner cruise -- typically releasing 250 g CO2 (pax-km) -- generates some 500 kg CO2, or 100 kg CO2 per night.

Using the same scenario, if a person flies by plane, they would emit 160 kg CO2 in an average airline trip. Adding hotel emissions would be 30 kg CO2 more per night, i.e. 150 kg CO2. The total would therefore be 310 kg CO2, or 235 kgCO2 if sharing a room. In this instance, an airline passenger would generate approximately 40% less CO2 than someone who flies and stays in a hotel. If this person shares a hotel room, the figure stands at over 50%.

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“At vessel level, cruise ships are probably the worst (polluters) since they have a huge energy demand associated with their hospitality services,” John Maggs, chairman of the Clean Shipping Coalition, a leading collaborative group working on shipping issues with the IMO, said in a press release.

According to Comer, new cruise ships are increasingly opting for Liquified Natural Gas, essentially methane, as a fuel. Actually, according to Clarksons University, half of all new cruise ships run on LNG. And while it reduces direct air pollution emissions, the engines used by LNG-powered cruise ships leak unburned methane (known as methane slip) into the atmosphere.

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Comer notes that the life-cycle emissions of these engines end up being higher than low-sulfur marine gas oil (diesel or diesel).

Research by Transport & Environment also concludes that fossil LNG as a marine fuel is “particularly problematic due to engine leakage or slippage”. According to the IMO, between 0.2% and more than 3% of diesel fuel is believed to leak from the combustion process to be directly released into the atmosphere.

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Many of the non-LNG-powered cruise ships use air purifiers or scrubbers that divert air emissions into the water. According to the ICCT, water discharged from the scrubbers is tainted with “polycyclic aromatic hydrocarbons and heavy metals that have been linked to cancers and reproductive dysfunction in marine mammals.”

Is there a future for electric vessels?

Yangtze River Three Gorges 1, the world's largest e-cruise ship.dfd

Elise Georgeff, a research associate with ICCT’s Marine team, explained to Bloomberg Línea that ship size and route length are the factors that most influence the feasibility of electric mobility for cruise ships.

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She notes that existing battery technologies satisfy the majority of coastal fleets, i.e. smaller ferries running short routes, which could drive the adoption of battery-electric ships. However, she says that “battery technology is critical in the more difficult-to-electrify segment: bigger ships deployed on longer routes.”

For her, the feasibility of electric mobility follows this equation: “Shorter routes = less energy = fewer batteries needed on board = better for smaller ships.”

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She notes that electric systems can be a viable option for long-distance maritime transit, although new and larger investments are needed for this purpose. “If a ship requires mooring at a dock or terminal for a period of time, there is a change for that vessel not to use its engines, but instead connect to the local grid and run on electricity. This is called shore power and is relevant to ships that require a lot of power while docked (especially cruise ships),” she says.

However, she notes that the real challenge lies on the open sea. “Depending on the length of the route, a ship is least likely to run on batteries alone. Then, you have to consider alternative energy technologies that may contribute to fuel savings, such as wind,” a source that has helped maritime transport in recent years.

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Georgeff believes that there will be room in the future for many zero-emission technologies, such as battery-electric ships, yet its potential depends on several factors such as the availability of alternative fuels.

“The types of ships that cover short, fixed routes and schedules -- such as ferries and harbor craft like tugboats -- will be more easily electrified, especially if shore power is installed. Long-haul ocean-going vessels, however, might use alternative fuels from renewable sources, such as green hydrogen or ammonia,” she says.

She says ICCT’s research suggest this future is feasible. “One study revealed that 43% of all container ships in the Pacific could complete their routes using only liquid hydrogen and fuel cells, and this number rises to 99% if an additional refueling stop is added. So battery electric ships are not the only option, large ships can also get to zero emissions with alternative fuels,” she says.

The fact is that there are already ships powered by electric motors that cover short distances and prove their efficiency on set itineraries. In terms of e-cruises, the Yangtze River Three Gorges 1 reinforces Georgeff’s notion. This is the largest e-cruise in the world with the largest battery capacity, and it can charge batteries on sea to complete its course.

This is relevant as supplying energy at sea is a major challenge to solve if electric cruise ships on long routes are to be viable. Maritime giant Maersk introduced a project based on a wind farm to recharge its own vessels in the middle of the ocean. This model could be replicated in the case of cruise ships.

How to reduce ship emissions?

Carnival's cruise ship Panorama docking at Long Beach, California.dfd

Georgeff says cruise ships could plug into the shore power grid when it is available (and where local grids can support the power demands of a ship of such size). It would also be ideal for cruise ships to switch to zero-emission alternative fuels, but she says “it’s not feasible until years from now”.

She stresses that it is key to reduce water pollution from cruise ships and to guarantee a standard along any routes and with all pollution sources. “Cruise ships going from Seattle to Alaska pass through Canadian waters, but Canadian discharge standards are not the same as those in the U.S., so they may discharge varying levels of pollutants depending on their location,” Georgeff said.

Environmental compliance is an important way to reduce the impact of cruise ships. Georgeff notes that Alaska had a program called Ocean Rangers: naval engineers who enforced compliance and reported polluting activities. These rangers were independent from the government. Though the program was scrapped, she believes the measure could be a viable option for a transition to more planet-friendly energy sources.

Meanwhile, the European organization Transport and Environment says that the transition also requires legislation to encourage investment in “green” infrastructure, so that sustainable fuels “are price-competitive and feasible” given that current costs are, it says, “too high” to compete with fossil fuels.