I'll check the train calculation it's a US website I think (didn't have many European airports I used Gatwick - Barcelona 6 return flights a year)
Most are there, they've just mangled the names somehow so search by city isn't reliable. The airport code or its "other name" may work.
e.g. Can't find Montpellier airport if I search for "Mont" but if I put MPL in it has "Mediterranee" (which is its other name).
2 return flights for me (skiing) and one down to Cornwall (oddly the flights were half the cost of the train[1] for this one).
I'm still ~7.5 ton of CO2 and the bulk of that is in the secondary calculations (6.47t); more than 1t of CO2 for each of food/drink, furniture, hotels/restaurants/pubs, banking/finance.
Going to Annecy again this year, all by train and we're done with flying down to Cornwall now they've moved the flights to LHR from LGW.
1. Second trip down we got the cheap train tickets so it was only £70 return for 3 of us.