Do you have a source on that? A source which takes into account "milk cows" being slaughtered and eaten after max. 4 years too? Accounting for the fact the cows only produce milk when having baby cows and some of these being male?

I am highly sceptical cutting meat is enough. Animal based protein, and energy is just inherently wasteful since 3/4 of intake energy is radiated away as body heat. (Yes, there is this super small niche of grass land unsuitable for humans feeding agriculture.)

I am not sure about the thermodynamics and ecology of fish in general, but I think eating predatory fish is an ecological disaster regardless of the carbon footprint.

Just to make sure, I don't think you have to quit all animal products for a sustainable future. If people go 95% plant based calorie-wise that's probably enough. Celebrate a steak once a month, commit to that, pay the real price for that!

"GHG emissions in kilograms of carbon dioxide equivalents per day (kgCO2e/day) were 7.19 (7.16, 7.22) for high meat-eaters ( > = 100 g/d), 5.63 (5.61, 5.65) for medium meat-eaters (50-99 g/d), 4.67 (4.65, 4.70) for low meat-eaters ( < 50 g/d), 3.91 (3.88, 3.94) for fish-eaters, 3.81 (3.79, 3.83) for vegetarians and 2.89 (2.83, 2.94) for vegans"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4372775/

I don't know what reduction is enough.

I think this study does not address my point and includes dairy products as their partial footprint of growing cow. The problem is: no meat, no milk.

The low footprint of vegetarianism only works as long as there are meat eaters eating the "milk cows". If everyone stopped eating meat, the dead cows would end up on the vegetarian's bill. I hope this doesn't sound stupid and you get my twist :)