The world's largest cruise ship sets sail for the first time this Saturday. But environmental groups are expressing concern that this and other giant cruise ships that run on liquefied natural gas (LNG) will leak harmful methane into the atmosphere in the future. Royal Caribbean International's Icon of the Seas, a 20-deck, 8,000-passenger ship leaving Miami, is capitalizing on the rapidly growing popularity of cruise travel. The ships are designed to run on LNG, which burns cleaner than traditional marine fuels, but there are concerns about the significant risks posed by methane emissions. Environmental groups argue that methane leaks from ships' engines pose an unnecessary risk to the climate, citing short-term harm. “This is a step in the wrong direction,” said Brian Comer, director of the oceans program at the International Council on Clean Transportation (ICCT). “We estimated that using LNG as a marine fuel produces 120% more life cycle greenhouse gas emissions than marine gas oil,” he said. As reducing greenhouse gas emissions is a key factor in maintaining global temperature stability, methane has an impact that is 80 times worse than carbon dioxide over 20 years. Cruise ships like Icon of the Seas use low-pressure, dual-fuel engines and leak methane into the atmosphere during the combustion process, a phenomenon known as "methane slip." Royal Caribbean claims the new ships are 24% more efficient than the carbon emissions required by the International Maritime Organization (IMO). LNG is said to emit fewer greenhouse gases than the very low sulfur fuel oil (VLSFO) that powers most of the world's shipping fleet. The cruise ship's engines convert natural gas into power in their cylinders, and "it is important to ensure that all natural gas is converted into energy," said Juha Kitula, director of R&D and engineering at Wärtsilä. “What is not converted can leak into the atmosphere during the combustion process, and Warzira’s natural gas engine technology now produces 90 percent less methane emissions than it did 20 to 30 years ago,” he added. A 2024 study funded by ICCT and other collaborators estimates that the average methane slip on a cruise ship is about 6.4%. However, IMO estimates the methane slip at 3.5%. “Methane is being looked at more,” said Anna Barford, Canadian shipping campaign manager for the Stand Earth non-profit organization. Last summer, the IMO pledged to address methane emissions in its greenhouse gas reduction efforts, including in response to climate change. said. It is expected that 63% of ships on order between January 2024 and December 2028 will be powered by LNG, with approximately 6% of the 300 cruise ships currently powered by LNG. New cruise ships are being designed to run on alternative fuels such as traditional marine gas oil, LNG or bio-LNG, which accounts for a fraction of U.S. fuel consumption. “LNG is only one part of the real strategy,” said Nick Rose, Royal Caribbean’s vice president of environmental, social and governance. “As the market changes, Royal Caribbean will use a variety of fuels,” he added.