WATCH: Alarming moment huge clouds of black smoke spew out of cruise ship in shock video

”It’s dangerous, it’s not a healthy thing for us to be exposed to,“ Ryan Kennedy, author of the report and an assistant professor at Johns Hopkins University Bloomberg School of Public Health, told CNN.

Carnival hit back at the claims, made in January, saying: “We test the air quality of our ships and they meet or exceed every requirement.

“The air quality on our ship decks when in port compares favourably with a typical urban or suburban environment. Independent testing on our funnels – which is the area where the exhaust originates- further validates our claims.”

Cruise Line International Accusation (CLIA) added: “At CLIA, we take our environmental commitment very seriously and will continue to focus on improvement in this area as a priority across the sector.”

“CLIA member cruise lines strive to ensure that each new generation of ships is more eco-friendly than the previous one and our members are committed to fitting existing ships with the latest technology as part of continued improvements across the industry.”

According to the CLIA website: “The cruise industry has invested $1 billion to develop and deploy innovative environmental technologies, practices, and cleaner fuels to help reduce air emissions.

“CLIA works with the International Maritime Organisation (IMO) to develop stringent requirements to reduce emissions from the global maritime fleet.