Shipping is the backbone of the global economy, carrying more than 80% of the world’s traded goods. But it also accounts for almost 3% of man-made carbon dioxide emissions. If the world’s ships are going to hit a key emissions reduction target, they’ll need to start burning clean fuels by 2030. The question is, which ones?

1. What are the front-runners?

Shipping’s fuel of the future must produce much lower or zero emissions, but also have enough power to propel gigantic vessels around the globe and be storable, transportable and affordable. Here are the main candidates so far:

• Ammonia

• Pros: Doesn’t produce 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 containment space, a challenge 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 engine or in a fuel cell

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

• Liquefied Natural Gas, or LNG

• Pros: Well-known, generally 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 infrastructure and causes methane emissions; bio and synthetic LNGs are also a possibility

• Biofuels

• Pros: Can be made from substances including vegetable oil and are compatible with several commercial marine engines and fuel infrastructure

• Cons: Generally more expensive than fossil fuels, and a major increase in production would be needed to meet maritime demand; lignin fuels (based on biomass residue and alcohols) may be price-competitive

• Methanol

• Pros: Liquid at ambient temperature so can be stored in 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 already used by some ships

• Cons: Fail-safe mechanisms are now built into reactor designs, according to ship classification society Lloyd’s Register. However, security concerns make them unappealing to governments.

2. What about renewables and other options?

Today’s batteries lack the energy density to power globe-trotting ships on their own. A large container ship would need the power of 10,000 Tesla S85 batteries every day, according to the International Chamber of Shipping. But electricity is still an option. The world’s largest electric ferry has entered service in Norway, while Asahi Tanker has ordered two vessels completely powered by lithium-ion batteries. Wind can also help. Maersk Tankers has fitted rotor sails -- giant pillars on deck -- to an oil tanker, saving about 8% of fuel. Cargill has said it plans to add so-called wing sails to some of its cargo fleet. Carbon capture and storage on vessels has also been mooted, with tanker owner Stena Bulk teaming up with the oil and gas industry to study its feasibility.

3. Why the urgency?

Because most vessels burn oil-derived fuels. The International Maritime Organization, shipping’s regulator, is targeting a 50% reduction in greenhouse gas emissions from 2008 levels by 2050 -- an effective 85% cut in CO2 emissions per nautical mile when increased trade is factored in -- and the complete phasing out of GHG emissions by 2100. Design and operational changes can help, but ultimately ships must start using cleaner fuels and the IMO has made only limited progress on this. Meanwhile, as part of proposals to curb greenhouse gas emissions, the European Union wants to include shipping in its Emissions Trading System, and the U.S. has also said it wants emissions from international shipping to drop to zero by 2050.

4. How much will this cost and who’s paying?

About $1 trillion to $1.4 trillion of investment will be needed between 2030 and 2050, of which the majority must be on land, according to University Maritime Advisory Services. In 2019, banks set up the Poseidon Principles as a framework for financing shipping. They require investors to align their lending books with a decarbonization target. The majority of signatories failed to hit the goal in the group’s first report. Meanwhile, shipping is looking to create its own $5 billion climate research fund, financed by a $2/ton charge on marine fuel. If approved, this would be the world’s first mandatory, global carbon levy, according to the World Bank.

5. What’s actually happening?

There are more than 100 zero-emission pilot and demonstration projects, many in Europe, according to the Getting to Zero Coalition, an industry group including more than 150 companies. It estimates that zero-emission fuels will need to make up 5% of the fuel mix by 2030 to put international shipping on course to align with the Paris Agreement’s goals. Maersk, the world’s biggest container line, says all of its new vessels will have to be capable of running carbon-neutral fuels as well as traditional oil-based products. It has also called for a CO2 tax for shipping of $150/ton, while commodities trader Trafigura has pushed for one of $250-$300/ton.

6. Who’s playing in this game?

Efforts to develop ammonia to power ships range from Greek company Avin International ordering a Suezmax tanker, which is set to be the first ammonia-ready vessel in the world, to Euronav aiming to have eight new oil tankers by the end of 2024 which will have the potential to run on the fuel. Amsterdam-based GoodFuels has supplied Volkswagen AG, Stena Bulk and others with marine biofuels and says they could make up as much as 15% of the marine fuel mix by 2030 and 25% by 2050. Engie SA and ArianeGroup SAS are developing hydrogen production equipment, while MSC Cruises is looking into the feasibility of the world’s first hydrogen powered, oceangoing cruise ship. Uniper SE and two other firms have partnered to develop green methanol as a maritime fuel in Europe. As of August, there were more than 550 ships powered by LNG in operation and on order, according to ship-classification society DNV. Maersk plans to have a small container ship capable of running on carbon neutral e-methanol or sustainable bio-methanol on the water in 2023.

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