Further, the 15 largest ships in the world emit as much nitrogen oxide and sulphur oxide as the world's 760 million cars. The problem isn't necessarily with the ships' 109,000-horsepower engines ...

Cruise ship engines have an estimated methane slip of ... Methane is a powerful greenhouse gas and is the second-largest contributor to climate warming after carbon dioxide, according to the ...

Engines on the world's biggest ships can be as tall as a four-storey house, and as wide as three London buses. So a lot of fuel is required, which in turn creates a large amount of CO2.