A transatlantic flight of 6 hours on a Boeing 737 would emit about 540 kilograms for a single passenger. In the US per capita C02 emissions were 15.8 metric tons in 2017. So the round trip would account for ~1/15th of a person's yearly total.

You could probably make that up by driving less, since a typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year. If you look at the UK, it's estimated that 20% of the nation's emissions are directly from heating and hot water, which is analogous to many areas of the US. This is largely due to old and poorly insulated housing stock.

This isn't meant to be CO2 whataboutism, but rather to compare meaningful individual contributions to emissions. IMO aviation for most international travelers may be a large single contribution, but they do it infrequently and other activities could be moderated of modified to make up ground. I mention this to support my parent claim that aviation has numerous benefits, and they may likely outweigh their costs accounting for externalities. That said, I would advocate a carbon tax that prices emissions into things like gas, heating, flying, etc.