Away with the ferries

The Isle of Arran, as I’m sure you all know, is on the west side of Scotland  Being an island, it has somewhat limited means of access: Caledonian MacBrayne run two ferries from the mainland.  These ferries are being replaced with allegedly better ferries. However, the BBC headline said ‘Green’ ferry emits more CO2 than old diesel ship

In reply, “Ferries procurement agency CMAL, which owns the ship, said the comparison was “inaccurate” as Glen Sannox is a larger vessel.” 

While New Zealand is very attached to per capita representations of everything, sometimes they aren’t helpful.  The new ship is bigger. Precisely for that reason, it would emit more CO2 if run on the same fuel as the old ship.  The plan is actually to run the ship on liquified fossil gas imported from Qatar and trucked up from the south of England. This would reduce the CO2 emissions, but would produce methane emissions that pretty much compensate for the reduction — and the UK follows mainstream science in recognising that methane actually matters.

In some settings, such as comparing Auckland’s double-decker buses to traditional buses, it’s important to take account of the fact that they’re bigger and so you don’t need as many of them to carry all your passengers.  But when you’re talking about a ferry route with two ships there isn’t the same room for per capita savings to pay off the larger per-ship emissions.   If you run the same number of trips with bigger ships you’ll get more emissions. And if you can carry more cars on the bigger ferries that’s not really going to reduce emissions, either.