The trade group representing the cruise ship industry unsuccessfully pushed international authorities to water down new environmental regulations despite its members' climate commitments, experts in marine air pollution warn.

Late last month, the International Maritime Organization rejected a cruise industry effort that would have improved cruise ships' carbon pollution scores. Environmental groups say it also would have led to more air pollution by allowing cruise liners to continue with business as usual.

The Cruise Lines International Association (CLIA) has membership that accounts for 95% of global cruise trips. Its four biggest members, Carnival Cruise Line, Royal Caribbean, Norwegian Cruise Line and MSC Cruises, tout their climate awareness and have all committed to drastically cutting emissions.

Yet according to a filing in April, the cruise ship association lobbied the International Maritime Organization's members to change proposed rules in a manner critics say will lead to increased emissions, while saving cruise lines money.

The International Maritime Organization is the United Nations body responsible for regulating the safety and environmental impact of shipping. Some 175 member states vote on its proposed legislation.

The proposed change would "certainly" have had a negative climate impact, said John Maggs, president of the Clean Shipping Coalition, an umbrella group of environmental groups that has official status at the maritime organization.

"The regulations are very weak anyway, and CLIA is trying to make them even weaker," said Maggs, who has almost 30 years in the field. "They are trying to water down the regulations."

But the cruise industry argues the new regulation misrepresents the efficiency of their vessels, which should not be penalized for spending more time in port than cargo ships.

Shipping emits about 2.9% of global carbon dioxide emissions, just over a billion tons of CO2 annually. Cruise liners produce more carbon dioxide annually on average than any other kind of ship due to their air conditioning, heated pools and other hotel amenities, studies have shown.

Carnival, which describes itself as "sustainable from ship to shore," has committed to reducing its carbon emissions 40% by 2030 to meet the terms of the Paris Agreement, which aims to limit global temperature rises to 1.5C.

Royal Caribbean and MSC Cruises have each pledged to meet net zero emissions by 2050, while Norwegian Cruise Lines has spoken of a "long-term goal" to reach climate neutrality.

Beginning in 2023, all large ships will be assigned a Carbon Intensity Indicator (CII), worked out by dividing CO2 output by the capacity of the ship and again by nautical miles traveled.

It will give ships an A to E sustainability rating. If a ship gets a poor rating, it has to submit a plan for how it will improve to at least a C, but there is currently no plan for penalties for badly-rated ships.

Nevertheless the trade group lobbied national delegations at the International Maritime Organization, which was established in the wake of the Titanic disaster, to make a special allowance for cruise ships. It argued their vessels differ from cargo ships because of the lengthy stays in port that are part of a cruise liner's existence -- typically with engines running to keep the lights on. This time in port hurts cruise ships' ratings, because they thus emit more carbon per mile.

"As a result, in-port emissions have a disproportionate impact" on a ship's carbon intensity grade, the industry told the agency.

Bill Weihl, a former sustainability chief at both Google and Facebook, who established Climate Voice, which calls on employees to pressure their companies into climate action, called it a familiar story for U.S. companies.

"They say — and sometimes do — good things on climate, while behind the scenes their trade associations obstruct and delay."

Two-thirds of cruise ships leave their engines running overnight while in port to power guest facilities. That affects not only the climate but air quality in port cities. The European city most polluted by cruise ship emissions with sulfur oxides and nitrogen oxides was Barcelona, topping a list of 50 affected ports, a 2019 report found. Two years previously some 32.8 tons of sulfur oxides was emitted there by cruise ships, the study said.

The cruise ship trade group argued that if its alternative proposal wasn't approved, the regulations that come into force in 2023 will create a 'perverse incentive' for ships to stay at sea longer to improve their rating. This could result in greater total emissions, they argue.

However, experts in marine air pollution say this argument does not hold water because operators cannot be fined for bad ratings, nor ships stopped from sailing.

"Additional time at sea means spending more on fuel. So it hurts their own bottom line," said Bryan Comer, who leads the marine program at the International Council on Clean Transportation. Long term, had the trade group been successful, cruise ships would emit more because there would be less incentive for them to invest in technologies that would reduce emissions such as shore power, fuel cells, and batteries, he added.

"They could continue business as usual and still receive more favorable scores that imply they are less carbon intensive than they are."

During negotiations over the legislation, Denmark, France and Germany had argued for stricter measures: that if a vessel languished in a D or E rating for too long, it should have its environmental certificate revoked, which would legally prohibit it from sailing.

Carnival spokesman Roger Frizzell denied any disconnect between the company's public statements on climate and the trade group's efforts before the maritime agency.

The company argues that complying with the rules as written could run counter to its objective to reduce real-world emissions.

"We peaked our absolute emissions in 2011," he said.

The firm said it opposes metrics that could create incentives to increase overall emissions.

During a port visit, carbon dioxide produced is much lower than during a voyage, Frizzell said. Yet cruise liners' pollution ratings will be sky high. That's because the distance being traveled is zero.

A statement released by the trade group said "CLIA and its cruise line members are fully committed to pursuing net-zero carbon cruising by 2050."

They support rating vessels by rate of carbon emissions in principle, but argue the current mechanism for doing so does not measure total carbon dioxide outputs.

"Our call is for the CII formula to be adjusted so it does not unintentionally work against absolute carbon reduction by potentially incentivizing cruise ships to improve their rating by traveling greater distances."

The International Maritime Organization invited the cruise ship industry to come up with a different proposal by 2026.

Royal Caribbean, Norwegian and MSC Cruises all made no comment, instead directing The Associated Press to CLIA's statement.

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