Planes, Trains & Boats

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Flying produces roughly 0.15kg of CO₂ for every mile that a single person flies. This is a massive simplification and relies on multiple assumptions, but it is one of the published DEFRA figure for cattle class, short-haul flights with a fairly full plane. However, this figure does not take into account the greenhouse effects of other aircraft emissions into the upper atmosphere, such as NO_x or vapour trails, which could push the figure up to 0.4kg of CO₂ (equivalent). Double this value again if you fly business class or even more comfortably.

In 2006 there were roughly 228 million air passengers flying from or through the UK. It is projected that by 2030 this will rise to 465 million. If these projections are reasonably accurate, it appears that by 2050 air travel will produce between 30 and 44 million tonnes of CO₂, not including the other aircraft emissions such as NO_x or vapour trails.

The plan is to cut the UK’s total CO₂ emissions down to 65 million tonnes by 2050m, which could be tricky if air travel is causing such damage. There is, of course, an easy accounting fix for this: the planes are travelling abroad, so just say the emissions are someone else’s problem. This currently appears to be the way out of the problem favoured by government.

On the bright side, planes are changing and becoming a lot more fuel efficient. In the short term this will mainly consist of using lighter materials and slightly better engines, but in the long term completely new aircraft designs could emerge and cut emissions by up to 50%. This is good news, but will still leave flying as one of the most damaging forms of travel.

There is a lot of disagreement about the emissions from trains, but the current situation for an intercity train with about 80% occupancy is around 0.05kg/km per passenger. This seems to be getting worse if anything, due to passenger trains getting heavier as they get more luxurious and fall under more stringent rail regulations, health & safety etc. There is even less information about freight trains, but a 2004 report by AEA Technology apparently concluded that freight trains produce a tenth of the CO₂ per tonne delivered as do lorries.

Buses produce about 0.08kg/km per passenger, with a London bus apparently producing a total of 1.4kg/km for the whole bus. This is a little bit strange as it suggests that London buses only carry 18 people; different sources using different assumptions, no doubt.

Ships have very little solid data about emissions, but it is interesting to note that 90% of the world’s goods travel by ship. Ships also produce 5% of the worlds CO₂ emissions (about 1100 million tonnes), as opposed to air travel’s 2% - but they do carry a lot more stuff. The only calculation on ship emissions I could make was from a Chinese, long distance ferry from around 2000, which appears to have given out 0.04kg/km per passenger.

For comparison, cars produce somewhere between 0.1kg/km and 0.5kg/km of CO₂ for the car as a whole, depending on type, condition and age.

Canal freight is on the up again, although not on a massive scale. For bulk goods it is a great thing, with some sand and gravel shipments in the north and around London doing well. Marks & Spencer have also used barges to take their waste cardboard from London to Birmingham for recycling, but I am not sure whether that continues. There have been a lot of canals revived lately, so barge transport is worth considering again for bulk, heavy cargoes that can be scheduled in advance, but there are some problems with canal-side residential developments squeezing so close to the water that cargo barges cannot use the locks anymore. Bit greedy, that.

Emissions compared

The following average figures are approximate, estimated and probably wildly inaccurate due to the complexities involved, but they should give some indication of the relative merits of the different forms of transport.

All figures in kg/km per person of CO₂ produced (or equivalent).

A more accurate but involved set of figures have been produced by DEFRA and are reproduced below; you can get the full story from DEFRA. There is some disagreement between the various figures as nobody can agree on exactly what to measure, how to measures it or when, so the odd pinch of salt is required here and there to season the claims.

DEFRA have also produced the following statistics for freight transport.

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