A couple of years ago, the Mediterranean Shipping Company (MSC) featured in a top 10 polluters ranking put together by environmental NGOs. Other entrants on the list were exclusively coal power plants.

But the biggest difference between big shipping companies like MSC and mega-polluting plants in Germany and Poland was the carbon market rules that apply to them. That is now going to change.

Currently, big industrial sites and energy producers have to buy emission permits for every tonne of carbon emitted. They get a big chunk of free allowances to help keep European industry productive but still have to pay substantial sums every year.

Earlier this year, permits topped €100 for the first time and although the price has since dropped, it is a far cry from the sub-€20 pricetag that was commonplace in the years after the market was first launched.

Shipping – which globally would be one of the top 10 polluters if the sector were a country – has for a long...