Tens of thousands of cargo ships will have to start using less polluting fuels in January, a boon for the environment that could however lead to higher bills for consumers.

The International Maritime Organization decided in 2016 that the sulphur levels in fuels for ships would have to fall to 0.5 percent in 2020, compared to 3.5 percent currently.

The idea is to reduce the emission of highly toxic sulphur dioxide -- a health hazard also responsible for causing acid rain -- by the nearly 80,000 cargo ships which ply the seas delivering raw materials and merchandise.