How many airports are landing anything like a 747 every 1.4 minutes? Especially given that the Shinkansen runs in both directions, so your airport is going to have to handle exclusively 747s, with high loadings and a headway of around 40 seconds. That's slightly more planes and massively more passengers than London Heathrow.

In terms of carbon emissions you'd need the flights to be long, and the trains to be pretty inefficient and empty (think current Amtrak trains), and even then there is evidence that the high altitude appears to make the emissions significantly more harmful than the equivalent ground-level emissions