On Saturday, the world’s largest cruise ship, Royal Caribbean’s Icon of the Seas, set sail from Miami on its maiden voyage. The nearly 1,200-foot-long and 250,800 gross-ton behemoth can accommodate close to 8,000 passengers across 20 decks.

The ship is the first Royal Caribbean vessel to be powered by liquefied natural gas (LNG), which the company claims sets a new standard for sustainability with the use of energy-efficient technology designed to minimize the ship’s carbon footprint and move closer to the company’s goal of introducing a net-zero ship by 2035.

That being said, environmental groups say methane leakage from the ship’s engines is an unacceptable risk to the climate because of its short-term harmful effects. (Natural gas is predominantly made up of methane.) 

“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, as quoted by Reuters.

At first glance, LNG used as a fuel appears to be a significant improvement over traditional heavy fuel used on cruise ships. LNG has a roughly 30% lower carbon footprint than bunker fuel and emits virtually no sulfur oxides (SOx) and particulate matter (PM). Compared to existing heavy marine fuel oils, LNG can, depending on the technology used, emit up to 95% fewer nitrogen oxide (NOx) emissions according to Sea-LNG, an industry group.

The problem with LNG as a marine fuel is what is known as methane slip. Methane slip is the escape of unused methane from an engine’s combustion chamber and other parts of the ship where it is stored and transferred. The fuel is not used by the engine so the methane escapes in its pure form to the environment.

As a greenhouse gas, methane is 80 times worse than CO2.

“We would estimate that using LNG as a marine fuel emits over 120% more life-cycle greenhouse gas emissions than marine gas oil,” Bryan Comer said.

Cruise ships like Icon of the Seas use lower-pressure, dual-fuel engines that leak methane into the atmosphere during the combustion process, according to industry experts. Engines used on bulk carriers or container ships emit less methane but they are too tall to fit in a cruise ship.

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 one piece of our actual strategy,” he said.

“People will say LNG is not the long-term fuel and we agree and view it as transitional,” Rose said. “We have built the ship to make it adaptable to future fuel sources.”

The company is preparing to debut the Celebrity Xcel next year, a 3,248-passenger ship that will be equipped with a tri-fuel engine designed to accommodate methanol, which several environmental groups consider to be one of the most promising fuels to achieve carbon-neutral sailing, reports the New York Times.
 

Thanks to Alaric Bond for contributing to this post.