New York:
The world's largest cruise ship will make its maiden voyage on Saturday, but environmental groups are concerned that the liquefied natural gas-powered vessel – and other giant cruise ships to follow – will leak harmful methane into the atmosphere.
Royal Caribbean International's Icon of the Seas departs from Miami with a capacity for 8,000 passengers across 20 decks, capitalizing on the rising popularity of cruises.
The ship is built to run on liquefied natural gas (LNG), which burns cleaner than traditional marine fuel, but poses a greater risk of methane emissions. Environmental groups say methane leakage from ship engines poses an unacceptable risk to the climate due to its damaging short-term effects.
“It's a step in the wrong direction,” said Bryan Comer, director of the Marine Program at the International Council on Clean Transportation (ICCT), an environmental policy think tank.
“We estimate that using LNG as a marine fuel emits more than 120% more greenhouse gas emissions over its life cycle than marine gas oil,” he said.
In terms of warming effects, methane is 80 times worse than carbon dioxide over 20 years, making reducing those emissions essential to combating global warming.
Cruise ships like Icon of the Seas use low-pressure dual-fuel engines that leak methane into the atmosphere during the combustion process, known as “methane slip,” industry experts say. Two other engines are used on bulk carriers or container ships that emit less methane but are too large to fit on a cruise ship.
Royal Caribbean says its new ship is 24% more efficient in terms of CO2 emissions than required by the global shipping regulator, the International Maritime Organization (IMO).
LNG emits fewer greenhouse gases than very low sulfur fuel oil (VLSFO), which powers most of the global shipping fleet, said Steve Esau, chief operating officer of Sea-LNG, an industry association.
Cruise engines convert natural gas into power in a cylinder, where it is “important to ensure that all natural gas is converted into energy,” said Juha Kytola, director of R&D and Engineering at Wartsila, which developed the cruise ship's engines.
What is not converted can escape into the atmosphere during the combustion process, he said, adding that Wartsila's natural gas engine technology emits 90% less methane than 20 to 30 years ago.
Cruise ship engines have an estimated methane slip of 6.4% on average, according to 2024 research funded by the ICCT and other partners. The IMO assumes a methane slip of 3.5%.
“Methane is coming under more scrutiny,” said Anna Barford, a Canadian shipping campaigner at Stand Earth, a nonprofit organization, noting that the IMO said last summer that its efforts to reduce greenhouse gases include tackling of methane gas emissions.
Of the 54 ships on order between January 2024 and December 2028, 63% are expected to run on LNG, according to the Cruise Line International Association. Currently, about 6% of the 300 cruise ships sailing are powered by LNG.
Newer cruise ships are being designed to run on traditional marine gas oil, LNG, or alternatives such as bio-LNG, which account for only a fraction of U.S. fuel consumption.
Royal Caribbean will use different fuels as the market evolves, said Nick Rose, the company's vice president of environmental, social and governance.
“LNG is part of our actual strategy,” he said.
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