[himinlomax]

I find the methane issue quite dubious: as it gets oxidized over time, the quantity of methane from cattle in the atmosphere is more or less proportional to the number of heads. The problem with CO2 otoh is that it keeps increasing because we create it from fossil sources.

[tsimionescu]

There are two problems with methane: for one, while it is "sitting" in the atmosphere, its greenhouse effect is much stronger than CO2's. After that somewhat short-lived period, it oxidizes to CO2 and water, so it still at best ends up as bad as CO2.

So even if we stopped producing CO2 from fossil fuels today, we would still be increasing the amount of CO2 in the atmosphere though breeding cows and other livestock, moving through a CH4 phase that does even more harm. Livestock are releasing the C trapped in plant bodies.

[himinlomax]

That carbon in cow farts & burps was grass yesterday, which was atmospheric CO2 last week. Cows are not fed petroleum products, though some petroleum may be used in the production of industrial feed (but not or much less for pasture feeding).

Atmospheric CH4 does not "do harm" as such, it's indeed a greenhouse gas that contributes to global warming in proportion to its prevalence. Said prevalence, as I'm trying to point out, is proportional to the number of heads of cattle. As such, if we don't increase the number of heads significantly, the impact will be constant.

Contrast with fossil fuels for, say, transportation: their impact on greenhouse effect is constantly increasing at a rate proportional to the number of cars/planes/trips.

Or put another way: we have to stop using ICE cars and planes altogether to stop increasing greenhouse effect; we only have to keep eating the same amount of beef and cheese to stop their impact.

[dTal]

But the C trapped in plant bodies comes from sequestered atmospheric CO2, no? It's not possible to permanently increase atmospheric CO2 purely through livestock, only "temporarily" increase methane (permanently, if we keep the livestock industry running forever).

There is only one place that actual surplus carbon comes from, and that is fossil fuels. Everything else is part of the closed-loop carbon cycle.