A boom in cruise liner holidays is raising concerns over the widespread use of “emissions dodging” by global shipping to meet tough new dirty fuel rules next year.

Royal Caribbean Cruises Ltd revealed this week it had received record bookings for 2019, with the boom sparked in part by a rise in Chinese passengers.

More than half a million Chinese passengers sail with Royal Caribbean every year. The company said it was seeing rapid growth in tourists wanting to take cruises in Europe and Alaska, and rising demand to tour the Caribbean.

The cruise industry – like the rest of the global shipping fleet – has to meet a deadline of 2020 to change from heavy sulphur fuel to more expensive low sulphur fuel to reduce toxic emissions. Many cruise ship owners are turning to the use of exhaust cleaning systems, known as scrubbers, rather than opting to buy cleaner fuel.

The controversial system has divided the industry. It uses seawater to “wash” dirty fuel before sending the washwater back into the ocean – or in the case of more expensive closed-loop systems, containing the washwater and disposing of it on land at regulated sites.

Singapore, Hong Kong and China have all banned the release of washwater from scrubbers into their waters to protect the marine environment, as have some Caribbean islands. Global NGOs called last month for a ban on scrubbers.

Analysts say about 90% of cruise ships are opting to install scrubbers to meet the IMO regulations which from 2020 will require ships to use fuel with a maximum sulphur content of 0.5%, compared with the current 3.5%. The IMO is allowing the use of scrubbers but there are concerns over the impact on the marine environment.

Many in the shipping sector believe this moves the pollution threat from the air to the ocean – and could be particularly damaging when “washed” fuel is released in congested waters like those used by many cruise ships. There is also concern on how the new regulations will be enforced.

Facebook Twitter Pinterest A cruise ship in Venice. Photograph: Marco Secchi/Getty Images

Paddy Rodgers, CEO of EuroNav, the world’s largest crude tanker company, said: “The cruise industry is not my sector but we are all in it together because the fuel standards affect all shipping. You will have a lot of argument in the shipping world that it is environmentally OK, but I struggle with this.

“No one has done any scientific work on a proper basis to see the impact of this. There were tests that have been taken by lobbying groups who have used limited sampling and testing to make their point.

“But we know that the byproduct that we are trying to get rid of is sulphuric acid, which is a pollutant. There are marine regulations to stop you putting it over a ship but with scrubbers, what they are doing is bringing the sea water on board, mixing the acid with the sea water and then pumping it out at sea. That is a monumental fudge.”

RCC, based in Miami, said this week 75% more Chinese guests were opting for a non-China itinerary in 2019, compared with three years ago.

RCC has revealed publicly that the company will be using scrubbers – described as “advanced emission purification” systems – to meet the 2020 regulations. Adam Goldstein, RCC vice-chairman, told the trade press the company planned to install them in up to 60-70% of its vessels by next year.

He said: “You inject tremendous amounts of water into the exhaust and it takes the sulphur away … that is our principal strategy.”

Shipping fuel emits significant amounts of CO2, sulphur oxides and nitrogen oxides, but also particulate matter containing organic carbon, black carbon, polycyclic hydrocarbons and heavy metals.

Friends of the Earth US said: “The cruise industry should be striving for the ceiling and not the floor when it comes to environmental protection, especially since it goes to some of the most pristine places on the planet and relies on those places to remain clean for it business.

“That means it should be installing better pollution reduction technologies like diesel particulate filters which don’t allow the ships to burn heavy fuel oil, they have to use cleaner fuel. Then you don’t have the generation of acidic scrubber sludge that can be discharged at sea, and the threat of a heavy fuel oil spill is significantly reduced.

“The industry is a contributor to climate change and they shouldn’t make it worse by adding acidic sludge to an already warming ocean. If they continue to insist on scrubbers then they should lead by creating facilities to dispose of the sludge on land and at the same time move away from heavy fuel oil for their fleets.”

In a statement RCC said: “We invest heavily in numerous technologies to reduce both emissions and energy consumption. Our ships are more energy efficient than they have ever been, and we are committed to sustainable practices across our company.

“We believe AEP (advanced emission purification) technology is the best approach to meet IMO’s 2020 regulations. The technology, which removes up to 98% of sulphur, allows us to operate in compliance in areas where compliant fuel sources may become limited. We continue to explore alternative fuel options, such as LNG and fuel cells.”