I don't think you can really consider the environment here as there are too many variables to consider in a reliable model. E.g. its not clear that replacing that entire planes worth of peoples trips with another routing would even net a gain, if people might have to do more circuitous routing that take more time and distance, or take different modes of transit that aren't a fully electrified rail that goes end to end, e.g. a lightly filled bus that has a much lower per passenger mpg than an airplane.

I understand that some comparisons with realistic assumptions have been made. Notably, high-speed trains cause significantly more emissions than classical trains, but are still better than planes.

Are high sped trains worth the extra capital and operating expense?

I love trains.