One reason is that users frequently give corrective upvotes (https://hn.algolia.com/?query=corrective%20upvote&dateRange=...), which leaves a complaint like this dangling as uncollected garbage.
Your other comments are great, so it would be nice if you would fix this.
A longer commute will generate more, being stuck in traffic will generate more, building new roads will generate more. A flight that is not cross-Atlantic will generate much less.
It’s not clear which way the balance will tilt, but you can’t just make blanket statement that planes will be worse than cars - you have to show your math.
A round trip from JFK to FRA emits about 0.91 t (910 kg) CO2 but if you account for radiative forcing [1] it is equivalent to 1.62 t (1620 kg) [2].
That's not to mention multiplying all these figures by 6 (for every 2 months), so that's 9720 kg.
I don't think it's a wash.
[0] https://www.nrc.gov/docs/ML1006/ML100621425.pdf
2. Few people will move form US to Germany. It's more likely someone will move e.g. from Portland to San Diego. 275kg roundtrip, 550kg adjusted for radiative forcing.
So if you fly 3 times per year it's a wash, if you fly 6 times a year it's double the CO2 emission.