@FreeMan: No mode of transport is completely environmentally harmless, but some modes of transport are much less environmentally harmful than others. See this link.

@FreeMan train travel gives off a tiny fraction of the emissions of plane travel.

Trains mostly run on electricity which can be made by greener ways than burning stuff. Greenest option is to stay at home. Next is walk or cycle. Next best is probably the train.

People, while I do not agree with the first comment in this series, claiming train travel is also damaging to the climate, it is a legitimate comment and should not be deleted. So please stop flagging it.

Don't forget that electricity in Germany and the UK is largely produced from fossil fuels. app.electricitymaps.com/zone/DE shows 416 g CO2/kWh in Germany, 47 in France, 270 in UK for the last 30 days. It's harder to find a value for kWh/km/train passenger, but it seems to be around 0,5 giving around 2,8 T CO2 for the journey.

@grahamj42 the number I've found is way less: around 0.11kWh per (passenger.km), over ~2000km giving 220kWh, or, assuming 300g/kWh, 66*kg*. (The overall is likely significantly lower, depending on how much of the trip is in France, and considering that DB claims that ICE run on 100% renewable electricity. That would take that number down to under 40kg)

@grahamj42 the one-way trip is on the order of 2000 km, even if I take 0.4 kg CO2/kWh the whole way and 0.5 kWh/km that gives me 0.4 tonnes each way (0.8 total). Not sure how you ended up at your number. The other point is: the trains are going either way, and the marginal increase in power use from one more passenger is much smaller than the equivalent on a plane. If demand really spikes you throw another car on the train, versus having to fly a whole other plane. Even just switching to a larger plane on the route is a big increase in fuel burned.

Why don't you just drive? It's much more convenient.

If you do train, be aware that a change of stations in Paris, is a nightmare dealbreaker. Don't forget that if you don't just go by car, you'll have huge inconvenience and expense on each end actually getting to/from anywhere. Scotland has no public transport to speak of (unless you happen to be going to the center of Edinburgh or Glasgow and that's it).

OP @Nick the answer to your question depends totally on whether you are a family travelling (say 5 or more people) or a young solo traveller.

As a curiosity does anyone know the flat our QUICKEST possible time, from central Munich (old town, the rathaus) to central Edinburgh (statue), using trains? (and/or obviously buses is needed for the connection ends) ... ?

Whether you choose to take the train or fly, the airline will still fly its scheduled flights. If it helps you feel better then do what you want, but don't delude yourself into thinking your personal choice has done a thing for the environment.

@Fattie - Scotland has no public transport to speak of (unless you happen to be going to the center of Edinburgh or Glasgow and that's it). Are you sure about that? I just came back from Aberdeen by train and had lots of choices.

@MichaelHarvey i'd put it this way, for a person living in or familiar with Munich (the OP?) or Copenhagen or Switzerland, then relatively Scotland is a "rural region" where you "need a car" to do much of anything. Sorry for leaving out the 3rd (and of course, by far best!) city (where my family's from!)

Exactly as @MichaelHall points out, not-flying IS A PROTEST MEASURE. To literally use the least enviro-whatever you should fly because self-evidently the plane is already flying and putting yourself on it uses zero enviro units. (Exactly the same applies for folks who feel you should not-use-train.)

@Fattie the train is also driving whether or not you are on it.

@MichaelHall change is made by the sum of many individual choice. Sure, one guy not taking one flight has no impact. But every single flight out there is made up of a hundred-plus people who individually chose to take a flight.

@Tom - yes, you may have missed where I stated exactly that, in the comment !!

@MichaelHall, Fatty This standard argument is frequently used, but not valid. By this you can justify nearly everything which has "only" a social or global impact. Avoiding consumption has a long-term and maybe more indirect impact (the chicken I don't buy is already dead, the electricity I don't consume was already produced, etc.). The impact is there because providers of transport (or electricity etc.) will consider their experience on needs. On the other hand, changing consumption attitudes show that it's possible. So one motivation is also trying to change by being an example.

At the scale of the individual it IS completely valid. But, I acknowledge that there is power for change in volume. (Obviously, because demand drives supply...)