Reasoning from first principles (physics), there is zero CO2 impact of food, including beef (especially discounting methane). Animals are part of the CO2 cycle

Reasoning from first principles (physics), there is zero CO2 impact of food, including beef (especially discounting methane). Animals are part of the CO2 cycle. They breathe out CO2, you eat meat and breath out CO2, grass consumes CO2 to grow, cow eats grass - loop complete. Of course, there are other inputs - e.g. transportation and fertilizer production (fun fact: 50% of the protein of your body is artificially produced, organic nitrogen bound via Haber-Bosch process). But those are energy inputs, not CO2 inputs. If we used nuclear/solar, farming would be CO2-neutral. All long-term climate change impact is coming from fossil fuels, not meat/farming. (Methane has only short-term impact.)