The world"s largest cruise ship has set sail from Miami, Florida, on its maiden voyage, but there are concerns about the vessel"s methane emissions. The 365m-long (1,197 ft) Icon of the Seas has 20 decks and can house a maximum of 7,600 passengers. It is owned by Royal Caribbean Group. The vessel is going on a seven-day island-hopping voyage in the tropics. Environmentalists warn the liquefied natural gas (LNG)-powered ship will leak harmful methane into the air. Although LNG burns more cleanly than traditional marine fuels such as fuel oil, there is a risk that some gas escapes, causing methane to leak into the atmosphere. Methane is a much more potent greenhouse gas than carbon dioxide. "It"s a step in the wrong direction," Bryan Comer, director of the Marine Program at the International Council on Clean Transportation (ICCT), was quoted as saying by Reuters news agency. "We would estimate that using LNG as a marine fuel emits over 120% more life-cycle greenhouse gas emissions than marine gas oil," he said. Earlier this week, the ICCT released a report arguing that methane emissions from LNG-fueled ships were higher than current regulations assumed. A powerful greenhouse gas, methane in the atmosphere traps 80 times more heat than carbon dioxide over 20 years. Cutting these emissions is seen as crucial to slowing down global warming. Royal Caribbean said the Icon of the Seas is 24% more energy efficient than required by the International Maritime Organization for modern ships. The company plans to introduce a net-zero ship by 2035. On Thursday, Argentina"s World Cup winning captain Lionel Messi, who currently plays for Inter Miami, took part in the ship"s naming ceremony. He was seen placing a football on a specially built stand to trigger the traditional "good luck" breaking of a champagne bottle against the vessel"s bow. Icon of the Seas cost $2bn (£1.6bn) to build. It now boasts seven swimming pools, six waterslides, and more than 40 restaurants, bars and lounges. — BBC