Is green shipping a contradiction in terms? To some environmental campaigners, it certainly is.

With more than 800m tonnes of CO2 emitted from the world fleet each year, other noxious exhaust emissions, open-loop scrubber wastewater, garbage dumped overboard and the beaching of scrapped ships, it is without doubt an industry that needs to clean up its act.

Yet it is undeniably — tonne for tonne of cargo moved — by far the most energy-efficient means of transport, far outperforming road and rail, let alone heavily polluting aircraft.