Shipping is the backbone of the global economy, responsible for about 90% of world trade. But it also accounts for almost 3% (and rising) of man-made carbon dioxide emissions. The industry’s regulator set a series of emissions-cutting targets back in 2018 aimed at driving a transition away from high-polluting fossil fuels. If the more ambitious goals are to be hit, the world’s ships will need to start burning new, clean fuel by 2030. The question is, which one?

1. What’s the fuel of the future for ships?

Ships burn about 5 million barrels of fossil fuel every day, pumping a constant stream of CO2 and other chemical nasties into the atmosphere. Yet figuring out the fuel of the future isn’t just about emissions. It’s got to have enough power to propel gigantic tankers around the globe, be storable and transportable, and, of course, not too costly. Here’s a list of the front-runners:

  • Ammonia
    • Pros: Doesn’t produce any C02 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 and so would need about three times as much space to contain the same amount of energy, a problem for ship designers; toxic for humans and aquatic life
  • Hydrogen
    • Pros: Is potent enough to send rockets into space and can be produced without CO2 emissions; can be used in a ship’s internal combustion engine, or in a fuel cell
    • Cons: Less energy dense than ammonia and 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 and some ships already use
    • Cons: Still a fossil fuel so it’s not carbon neutral, although bio and synthetic LNGs do exist. Also needs costly infrastructure and causes methane emissions
  • Biofuels
    • Pros: Made from the likes of vegetable oil and compatible with several commercial marine engines and bunkering infrastructure
    • Cons: More expensive than fossil fuels and a major increase in production would be needed
  • Methanol
    • Pros: Liquid at ambient temperature so it can be stored in regular, non-pressurized tanks; can be made cleanly and is in use in some ships
    • Cons: Less energy dense than oil-based fuels and the clean version is much more 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 weeks on a nuclear-powered ship?