If you are serious about climate change, stay at home. There are only two solutions...
1. Drastically cut consumption of everything (including travel) for everyone on the planet.
2. Drastically shift the fuel mix for power generation to nuclear.
Calculating CO2 output on a incremental basis is not sustainable, you have to look at life cycle costs like road construction, production of steel rails and and concrete ties, gas consumed by air traffic controllers during their commute, mining lithium for Tesla batteries, paving runways, etc., etc.
Regarding train travel, unless you have extremely high population density (maybe two or three places on the planet) which will justify high frequency (think one train every 5 to 10 minutes) and high capacity (1500 pax) trains, the carbon footprint of building the infrastructure is phenomenally high on per mile traveled basis.
For those interested, average jet fuel consumption is 20% of weight (passenger plus baggage) per hour of flight. On an incremental basis it's 5% percent. So assuming a 10 hour RT flight for an average pax+bags of 200 pounds that's 400 pounds (60 gallons) of jet fuel which when burned produces roughly 1200 pounds of CO2.
If you are talking about getting rid of straws, solar panels on your house, driving instead of flying, then you don't have a clue and are BIG part of the problem.