(originally written as a FB note, hence some argument that will already be familiar to many here)

Here’s a back-of-the-envelope comparison of plane and train journeys in light of some new (to me) information from EAA:

According to a highly authoritative source (ie top Google hit), train journeys are around 19 times as efficient* per distance travelled as taking a plane would be. Extrapolating from those figures (which are somewhat suspicious given the discrepancies between them when you’d think plane journeys would be pretty direct), an hour in the air is equivalent to something in the region of 175 KGs of CO2 emitted. Overland times will obviously vary more depending on the route you have to take, but seem to average at about 10 kilos of CO2 emitted in one plane-hour’s worth of train journey. Quite a difference.

But a very quick look at Ryan Air’s/EasyJet’s sites suggests you can get to, say Germany and back for about £55. The same journey by train would apparently cost about £86 – about 1.5 times as much, allowing for a few inevitable excess fees from Ryan Air. It seems like there’s good reason to be sceptical of typical offsetting options, not least because they allow for a certain amount of greenwashing by the airlines. But according to Effective Animal Activism’s latest estimates, giving approximately £4.60 ($7.40) to their top rated charities averts a tonne of CO2. This is, ostensibly, a *side-benefit* – their main purpose for those who support EAA’s charities is reducing very large amounts of animal suffering - which I hope the inevitable critics of the uncertainty of offsetting will consider. Nonetheless, taking it at face value as the only gain, this means that if you pay, say, £65 for the plane ticket and give the £20 saved towards these charities, you’ll have the net effect of reducing effective CO2 emissions by roughly 4 tonnes compared to the comparative neutrality of taking the train.

But that doesn’t account for the time saved – imagine that you might have done paid work, or perhaps money-saving labour with the extra time you gain from flying. Broadly speaking, the further you travel, the greater the proportion of time you seem to save, so it’s hard to generalise. A four hour flight, according to that page, could be anything between 8 to 15ish hours. So let’s say the plane saves you approximately 6 hours. What this is worth depends largely on your income, and how productively you use your free time. If you earn £10 an hour and use free time at about half your employment efficiency (ie you do about half the good with your free time as you would by just donating the salary of your equivalent working time), the difference between plane and train is just over another 6 tonnes of CO2 averted for a gain of about 10 tonnes averted CO2 compared to taking the train.

*accounting for the effect of emissions higher into the atmosphere.

Arepo wrote: an hour in the air is equivalent to something in the region of 1.75 tonnes of CO2 emitted

... do you mean for the airplane? based on the numbers in one of your links, I get about 60 Kg of CO2 per hour per passenger for air travel, but the per-hour number would become increasingly inaccurate for short flights (due to the fixed cost of getting to cruising altitude). If the number were 1.75 tonnes per passenger, then a plane on an 8 hour flight would have to carry too much weight to fly.

Regardless of that number, the ratio of plane to train seems reasonable.

Hm, I think I forgot to carry a one

Should be about 175 kilos of CO2 - the 60 you mentioned (I went with 65 I think) multiplied by the factor of 2.7 he gives for it being released higher into the atmosphere. I've fixed the OP.

Note, however, that, for most people, free time is wasted. Not only that, but airport security is such an amazing hassle that it can truly sap your energies. The same for the logistics. Airports are often far outside cities, so there's at least an extra half-hour involved coming and going.

Flying is a pain in the neck, and this reflects on your productivity.

Trains, however, are amazingly simple and straightforward, and you can usually board them from somewhere close to the very heart of the city.

Planes are good for international travels, but on anything smaller than six hundred kilometres, I'd say that trains are optimal.

As a matter of fact, the relative cheapness of trains could be enforced by the State taxing the difference from the airline companies, funding the difference for the railroad companies, or anything in-between. If it's done by taxing, and people still prefer flying, the difference could be explicitly used to finance efforts that are optimized towards CO2 emission reduction. The State is often useful in such "Tragedy of the Commons" situation, where most people would go "I'm definitely not paying the difference to charity X and I'm certainly not dedicating my free time to do good", but, when proposed the plan, might say "that is quite a virtuous plan, and I would vote for it".

For most people this won't apply - the reasoning only holds if you're a utilitarianesque consequentialist or prepared to act like one in certain scenarios (eg this).

You can also suggest it to people in specific circumstances – for eg I was prompted to think about this in part by some friends insisting on taking a train for a holiday we were trying to organise, where they would have done better and saved a lot of time and organisational difficulty for the rest of us by committing to give the difference. One simple way of doing this is to have one (utilitarian) person book flights for everyone on the above understanding, and ask them to send him the full cost inc donations, which he’ll then make in one lump sum.

Well, if the decisive reason for taking the train was saving CO2, rather than, you know, comfort, ability to walk around, more ease for meeting new people, and so on, then it's a reasonable conclusion. Otherwise, it's disputable. And, heuristically, I feel reservations about a "break and mend" polcy as opposed to a "don't break in the first place" approach.

Am I right in assuming that utilitarianism is, in practice, largely about detecting where heuristics that work well for daily problems stop working, and what to do instead in those situations? When do we come up with better heuristics for normal moral conundrums?

Right, I'm only thinking about environmental (or rather utilitarian) reasons for choosing here.

I think what utilitarianism is in practice depends a lot on the circumstances of the individual considering it. Personally I see little value in self-imposing heuristics (usually if you're in a situation where there's any doubt about whether to apply one, you're effectively calculating already, and there's little value in precommiting yourself) - with the possible exception of avoiding (or rather compensating for) cognitive biases.

with the possible exception of avoiding (or rather compensating for) cognitive biases.

Such as in the case of ethical injunctions, along the lines of . "don't do generally bad thing X for specific good outcome Y, especially if it seems like a clever idea"?

Yeah, for example. Or don't stake too much on my getting something right that other people have got wrong.