Shipping is the backbone of the global economy, responsible for about 90% of world trade. But it also accounts for almost 3% of man-made carbon dioxide emissions. If the world’s ships are going to hit targets for reducing emissions, they’ll need to start burning clean fuel by 2030. The question is, which one?

1. What are the front runners?

Shipping’s fuel of the future must produce lower or zero emissions, but there’s more to it than that. It’s also got to have enough power to propel gigantic ships around the globe, be storeable and transportable, and, of course, not prohibitively expensive. Here are the main options so far:

• Ammonia

• Pros: Doesn’t produce any CO2 emissions when made cleanly, which can be done by combining so-called green hydrogen with nitrogen from the air

• Cons: Much less energy dense than traditional fuel oils so would need about three times as much space to contain the same amount of energy, a problem for ship designers; it’s also toxic for humans and aquatic life

• Hydrogen

• Pros: Powerful enough to send rockets into space and can be made without emitting CO2; can be used in a ship’s internal combustion engine or in a fuel cell

• Cons: Needs to be stored at either -253 degrees Celsius (-423 Fahrenheit) or under high pressure, so another major headache for shipbuilders; it’s also potentially explosive

• Liquefied Natural Gas, or LNG

• Pros: Well-known, readily available, lower CO2-emitting alternative to oil-based fuels that some ships already use

• Cons: Still a fossil fuel so it’s not carbon neutral, needs costly infrastructure and causes methane emissions; bio and synthetic LNGs also exist

• Biofuels

• Pros: Made from the likes of vegetable oils and compatible with several commercial marine engines and fuel infrastructure

• Cons: More expensive than fossil fuels and a major increase in production would be needed to meet maritime demand

• Methanol

• Pros: Liquid at ambient temperature so it can be stored in regular, non-pressurized tanks; can be made cleanly and is already in use in some ships

• Cons: Less energy dense than oil-based fuels and the clean version is expensive

• Nuclear

• Pros: Zero emissions, extremely power dense and is already used by some ships

• Cons: Fail-safe mechanisms are now built into reactor designs, according to ship classification society Lloyd’s Register, but would you want to spend months working on a nuclear-powered ship?

2. Why has shipping got to make this switch?

The Intergovernmental Panel on Climate Change has said that human-caused greenhouse gas emissions would need to be net zero by around 2050 if global warming is to be limited to 1.5 degrees Celsius. Meanwhile, the overwhelming majority of ships burn oil-derived fuels. The International Maritime Organization, shipping’s regulator, has targeted a 50% reduction in emissions from 2008 levels by 2050. Since trade is forecast to grow, the target requires as much as an 85% reduction in emissions, per vessel, by 2050. Some gains can be made by design and operational modifications, but ultimately vessels must start using cleaner fuels. Zero-emission ships will need to begin hitting the water by 2030, according to the Getting to Zero Coalition, an industry group including more than 120 companies. Other IMO targets include cutting CO2 pollution per transport work (a measure of distance covered multiplied by cargo) by 40% by 2030. By 2100, it wants the industry to be carbon neutral.

3. What’s happening on the ground?

Things are hotting up. As of late August, there were 66 zero-emission pilot and demonstration projects underway, the vast majority in Europe, according to the Getting to Zero Coalition. The full list wasn’t made publicly available, but here are some notable projects:

• Biofuels

• Oil giant Exxon Mobil plans to sell marine biofuel oil

• Mediterranean Shipping Company began using biofuels in Rotterdam last year

• Eastern Pacific Shipping is testing biofuels on an MR tanker; testing will expand to other vessel classes in the near future

• Ammonia

• A group of companies agreed to jointly develop ammonia-powered ships

• Separately, Lloyd’s Register has given approval in principle to three ammonia-fueled ship projects: two ultra-large container ships and a tanker

• Finnish company Wartsila is testing ammonia in a marine engine

• Hydrogen & Methanol

• French energy giant Engie is developing hydrogen production equipment and will promote the gas as a clean marine fuel

• Japan’s NYK Line is part of a group developing a fuel cell powered tourist ship

• The Port of Antwerp ordered a tug boat that will burn hydrogen in combination with diesel and is retrofitting another so it can run on methanol; it’s also investing in green methanol production

4. Any other developments?

Carbon capture and storage on vessels has been mooted. Tanker owner Stena Bulk has teamed up with the oil industry to study its feasibility, and a Japanese shipping company plans to deploy a small-scale CO2 capture demonstration plant on one of its ships. In other news:

• Countries have been meeting virtually at the IMO to try and reach an agreement on how shipping can cut its emissions.

• The European Union wants to include “at least intra-EU maritime transport” in its emissions trading scheme. Critics say the approach risks undermining a global approach to cutting emissions

• Shipping is looking to create its own $5 billion climate research fund, financed by a mandatory $2/ton tax on marine fuel over a 10-year period

• Top energy and commodity firms agreed to disclose the alignment of their shipping activities with the IMO’s climate goals

• Oil Trader Trafigura has called for a tax on shipping fuels of $250-300 per ton of CO2

• Maersk wants to have net-zero emissions from its operations by 2050

• Oil giant Shell wants the regulator to toughen its emissions target to being net zero by 2050

• Maersk, Cargill and others are launching a research center to focus on clean fuels

5. What about electricity, wind and solar?

Electricity won’t work for deep sea shipping. The batteries needed to power giant tankers for weeks on end would have to be enormous. And if you shrunk the batteries and relied on wind and/or solar to recharge them along the way, you’d run into a problem mariners have faced since time immemorial: the weather doesn’t always do what you expect. It’s not to say there won’t be some wind or solar usage, but only enough to power subsidiary systems, leaving the main engine with the sole task of getting the craft from A to B.

6. How much will it all cost and who’s paying?

About $1 trillion to $1.4 trillion of investment will be needed between 2030 and 2050, according to University Maritime Advisory Services, of which the vast majority will be on land. The split highlights a chicken-and-egg situation: Shippers are happy to build vessels provided they can guarantee the fuels will be available, but energy companies don’t want to provide fuels unless there’s a market ready for them. In 2019, banks set up the Poseidon Principles as a framework for financing shipping, requiring investors to maintain their lending books in a way that matches goals in the Paris climate agreement.

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