The overnight ferry from Aberdeen to Lerwick, in Shetland, stuffed full of vehicles and visitors, uses 60 tonnes of fuel – that’s one gallon for every 45ft travelled. And as modern ships go – and there are up to 100,000 – this one is just a tiddler.

Apparently, we take little notice of the global shipping traffic as it’s mostly out of sight, over the horizon, and in international waters. Because of this, it has escaped the legislation that is attempting to limit the amount of CO2 produced. No country includes the CO2 from its own ships in its national targets, nor that from other ships that serve it, and this is a serious omission.

New figures show that shipping is now responsible for about five per cent of the main greenhouse gas, CO2, and that means it produces double the amount from the world’s airlines, more than twice the amount from the whole of the United Kingdom and comfortably more than from the whole of the continent of Africa. It’s about the same as from cement production, and generally goes unnoticed.

One reason why we need to address this situation is because the international fleet is expected to grow by at least a third in the next ten years, with the development of much larger bulk carriers, for oil, iron ore, coal, grain and wood, and the even larger container ships trading with the Far East. The latter can carry up to 15,000 containers each and they are enormous.

The main reason, though, is the nature of the fuel used. It’s a form of diesel, but much cruder, and in the form of heavy fuel oil it’s the residue left at the refineries once the petrol has been removed. This bunker fuel, rather like tar, is thick and cheap, and as it doesn’t catch fire easily, it’s favoured by shipping lines.

The downside, apart from the carbon dioxide produced, is the amount of sulphur from the bunker fuel, which at just below five per cent is 5,000 times more than the sulphur allowed from car fuel. Indeed 16 of these super-sized ships pump as much sulphur into the atmosphere as all the cars in the world.

The thick black smoke leaving the funnels is made of very small particles of sulphur and carbon which cause serious respiratory problems when breathed in, as well as absorbing sunlight, to produce heating on the one hand, and reflecting solar energy away on the other.

A way forward might be to reduce speed by a third, and so burn less fuel, but the real answer must be to use fewer raw materials, make goods at home and reduce imports.