Cruise lines have made the case for their environmental efforts following analysis that claimed emissions from European vessels were far outstripping those from all the continent's cars.
Green group Transport & Environment (T&E) said research showed that in 2017 Carnival Corp's ships emitted 10 times the sulphur oxide of the 260m-strong vehicle fleet, with Royal Caribbean at four times.
Industry body Cruise Lines International Association (CLIA) said it and its members are committed to a zero-emission future.
