International shipping

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Around three per cent of global greenhouse gas emissions on the International Maritime Organization's own accounting, and the most energy-efficient way yet devised to move mass over distance — which is precisely why it is difficult. A large container ship or bulk carrier burns residual fuel oil or marine gasoil in a slow-speed two-stroke diesel at thermal efficiencies above fifty per cent, better than almost any other heat engine in commercial use, and it carries fuel for voyages measured in weeks. Batteries are viable for ferries and short coastal work and nothing else. The candidate replacements are all liquid or liquefied: liquefied natural gas, which cuts carbon dioxide modestly and risks unburned methane slip; methanol, which is easy to handle and is being ordered in dual-fuel newbuildings, with the first purpose-built methanol container vessel delivered to Maersk in 2023; and ammonia, which contains no carbon at all but is toxic, has a low flame speed, and produces nitrogen oxides and potentially nitrous oxide on combustion. Wind assistance through rotor sails and rigid wings is a real if partial saving. The sector's distinguishing feature is governance: because ships are internationally flagged and operate outside national jurisdictions for most of their lives, its emissions are regulated by a United Nations agency by negotiated treaty instrument rather than by any single state, which makes progress slower and more consequential at once. Not a place.