LONDON—The International Maritime Organization is mulling a new tax on shipping to help build a global network of alternative fuel stations for vessels and subsidize developing countries facing higher export costs.

The proposal calls for charging vessel operators $100 for each metric ton of carbon dioxide emitted per trip. The shipping regulator said the levy could raise around $1 trillion over the next three decades, according to a World Bank study submitted to the IMO in September.

The...

LONDON—The International Maritime Organization is mulling a new tax on shipping to help build a global network of alternative fuel stations for vessels and subsidize developing countries facing higher export costs.

The proposal calls for charging vessel operators $100 for each metric ton of carbon dioxide emitted per trip. The shipping regulator said the levy could raise around $1 trillion over the next three decades, according to a World Bank study submitted to the IMO in September.

The IMO has been under pressure from governments, big cargo owners and others to speed up efforts to drastically cut greenhouse emissions, but the agency’s head said little can be done if there is no money to fund the transition.

“Those who say we are dragging our feet are misinformed,” Kitack Lim, the IMO’s secretary-general, said in an interview. “If the developed world wants a faster track, they have to assess and address the economic impact on developing countries. The IMO is not a company that makes its own decisions, we have 175 member countries and we need consensus.”

The levy discussions at the IMO began in October as part of a range of market-based measures to finance the industry’s green transition. The matter will be discussed later this month at the body’s Marine Environment Protection Committee, which has a decisive voice over the panel’s timeline to cut carbon emissions.

If the committee backs the levy, it would set the stage for a consensus decision over the next two years among IMO members to adopt it.

The IMO has said that it aims by 2050 to cut in half the carbon dioxide emitted in 2008 by the world’s more than 60,000 cargo and passenger ships. Mr. Lim said that time frame will likely be revised in 2023, with a number of members pushing for the industry to set a target of net-zero emissions.

Developing economies, including Brazil, Argentina, Chile and a host of African nations, say aid is needed because a rapid shift in industry operations would harm their export-driven economies by making food and other commodities more expensive to move. Fuels like biomethanol, hydrogen and ammonia are also in short supply and cost at least twice as much as conventional bunker oil.

The shipping industry accounts for an estimated 2.5% of all global greenhouse-gas emissions.

Photo: Hollie Adams/Bloomberg News

Mr. Lim said the production of carbon-neutral fuels will scale up substantially over the coming years as energy majors are investing heavily in alternatives to crude oil. The shipping industry accounts for around 2.5% of all global greenhouse-gas emissions, according to the regulator, about as much as the average of a major European Union country.

“The new green ships will come much faster,” Mr. Lim said of the levy.

The levy proposal gained support at the COP26 climate conference in Glasgow, Scotland, this week with more than 50 countries from Asia, the Caribbean, Africa, the Middle East and Latin America, officially endorsing it.

Mr. Lim said the IMO should manage the funds collected through the levy, but that there hasn’t been much discussion on how the funds would be disbursed to developing nations.

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He said that from his consultations so far, the majority in the shipping industry prefer a levy on the price of bunker fuel instead of other proposals under consideration as a means to finance the green transition.

Some industry executives are calling for those efforts to move even faster.

“We need to get the IMO to be much more ambitious in terms of setting targets,” said Soren Skou, chief executive of Denmark’s A.P. Moller-Maersk

A/S, the world’s biggest boxship operator. “We can get a 50% reduction in CO2 emissions by 2030, two decades ahead of the current timeline.”

Maersk’s annual bunker-fuel usage results in about 36 million tons of carbon dioxide emissions, which means the levy could cost it roughly $3.6 billion a year.

Mr. Skou said that Maersk has proposed a $150 levy, but he said that if the $100 fee is adopted it would be a “huge step forward.”

Ship operators usually pass higher fuel costs to cargo owners. Mr. Skou said that with the $100 levy added, a container with 8,000 sneakers could cost an additional 10 cents per pair of shoes.

“The inflation for the consumer will be perfectly manageable,” Mr. Skou said.

Write to Costas Paris at costas.paris@wsj.com