[belorn]

A single trip between Paris and Nantes is calculated (using some random website) to be between 0.1-0.3 tons of Co2 per person on the plane.

Using some other random website, the same trip for one person on train is calculated to be 2kg.

So that makes it a factor of about 100x. How much could the tax be that would still make it distinguishable from a ban? How would people react if say the tax would be 1€ per kg?

[version_five]

This is the wrong way of looking at it. What is the cost to offset or sequester that 0.1-0.3 tons? That should be the worst case premium.