And that’s before we even start worrying about the carbon dioxide that’s emitted. This which adds up to more than 1 billion tonnes a year, roughly the same as aviation and the container ships are the worst offenders.
“Marine Diesel Oil” is a much cleaner fuel, and is often used when close to land or in harbour, but, although pollution is singnificantly reduced, there is little benefit in terms of efficiency and thus in greenhouse gas emissions. There are some practical and operating changes that can help:
* bow profiles altered to reduce hydrodynamic drag,
* containers packed more efficiently,
* travelling only when full and rerouting to avoid bad weather.
The simplest and most effective of all would simply be to reduce speed by 50%. This would reduce fuel use by two thirds.
Electric power of some sort would of course be an ideal solution, though battery power is only practical with short haul ferries with less than 20 miles between ports. Hydrogen plus fuel cells might be usable in the future but currently it remains inefficient, expensive and hampered by the fact that most hydrogen supplies come from methane steam reforming. This is even less green than using methane directly in diesel engines, which could well turn out to be a useful intermediate technology. It would produce about a quarter less carbon dioxide than either marine diesel oil or bunker fuel – and would be certainly a lot cleaner than the latter.
Natural gas, or methane, is, however, a very powerful greenhouse gas – although it persists in the atmosphere for a lot less than carbon dioxide. However, many shipping companies are concerned that leaks from tanks and pipeworks could make the problems worse. This consideration has led several to experiment with supplementing some of its bunker fuel with treated used cooking oil (UCO).
Eventually, as more surplus electricity arises from wind turbine farms, this could be usefully used to to produce hydrogen by hydrolising water, despite the inefficiency. Then the hydrogen, or, in another variant technology, ammonia, though toxic, could be used to generate electricity in fuel cells.
One way or another the carbon burden and pollution from shipping must both be reduced – and at a faster rate than the current piecemeal solutions described above are achieving!