This is true in some sense but in US flying is probably most peoples' greatest carbon contribution. A single round-trip flight across the US emits about the same carbon as you save going vegan for an entire year. This is also the amount emitted by commuting a half hour to work by car 3x/week for a year.
It is definitely the case that almost everybody would have to be entirely vegan in a world that takes climate change seriously. Half-Earth Socialism did the math on this; it's a simple constraint problem.
I did some googling, not crosschecking sources, just some napkin math
Taking a passenger flight from NY to LA and back - 0.62 tons
Average american eats a 124kg of meat a year and 1 kg of beef (not counting other meats cause lazy) needs 100kg of CO2.
So a year of beef is equal to 20 roundtrips (exactly). Though the real number is probably a lot less since beef is the worst meat if you don't want CO2, then you'd need to remove the emissions from the vegan diet
Its that 100kg factoring in the CO2 that is absorbed in growing the feed? Seems way too high per kg. (Yes widespread veganism is a requirement for managing climate change though. )
Looks like it's CO2 equivalent, so it includes methane which will inflate the numbers a lot. This is a neat chart
Another thing to consider is that people get pretty upset that the Amazon is burning. No one mentions what it's being burned for though.
These estimates vary quite a bit. Here's a 2023 paper in Nature studying climate impacts of various diets for people in the UK (not US): https://www.nature.com/articles/s43016-023-00795-w
Dietary impacts of vegans were 25.1% (95% uncertainty interval, 15.1–37.0%) of high meat-eaters (≥100 g total meat consumed per day) for greenhouse gas emissions
Vegans emit 2.16 kg/day while heavy meat eaters emit 7.28 kg/day of CO2 per this table.
Heavy meat eaters: 7.28 kg/day * 365 days/year = 2657.2 kg/year
Vegans: 2.16 kg/day * 365 days/year = 788.4 kg/year
Difference: 1868.8 kg/year saved by going vegan
600 kg for a round-trip cross-country flight seems about right, checking various city pairs on google flights. So here the estimate is more like 3x round trip flights. Other references I've seen make it closer to 1-1.5x. Actually if you choose the low meat eaters emissions from the same table (4.21 kg/day) that comes to 1-1.5x round trips.
