[svara]

From https://en.m.wikipedia.org/wiki/Individual_action_on_climate...

""" Several scientific studies have shown that when people, especially those living in developed countries but more generally including all countries, wish to reduce their carbon footprint, there are a few key "high-impact" actions they can take such as: having one fewer child (58.6 tonnes), living car-free (2.4 tonnes), avoiding one round-trip transatlantic flight (1.6 tonnes), and eating a plant-based diet (0.8 tonnes). These differ significantly from much popular advice for "greening" one's lifestyle, which seem to fall mostly into the "low-impact" category. """

... although I have seen air travel clearly dominate car use in other sources. Obviously it depends on how you use the car and what type it is.

Also, not having children being so impactful seems to assume that emissions are proportional to population, which seems doubtful to me (haven't looked into the original sources though).