According to one model, the climate impact of a transatlantic flight could cost global economy $3,000 over the course of this century.

That number embodies assumptions which may not be true. If civilization collapses by 2060 with or without the flight, the flight's ultimate impact might be zero. If civilization survives enough to talk about the impact of any specific act, that impact could vary depending on other details.

I wonder what the likely impact of having a child would be. According to the study which estimated the expected impact of one child as 2880 translatlantic round trips, it would be 2880 * 2 * 3000, which is 17,280,000. Rounded to one significant figure, that is 20 million dollars. But I suppose that could be off by a factor of 5 or 10 in either direction.