Given the tonnage of CO
2 we pump into the atmosphere, I cannot see how we can deny that we're causing the CO
2 increase.
Are you telling me that the 7 billion people and the equivalent 700 billlion chicken per year needed to feed them (using chicken for equivalency, don't want to list quantities of all livestock) are not incremental to the average of 250 million people and their livestock that had been the average population of humans for most of their history.
I don't think so, but I'm not really sure what you're asking.
The fossil fuel requirements of keeping people fed is certainly contributing to global warming, though the 'food' aspect of fossil fuel usage is not the major consumor of fossil fuels. However, in general, eating is not a CO
2-increasing activity. All CO
2 I breathe out was a plant within the last year, and new plants will be grown to feed me next year. It's a zero sum game.
If I eat a cow that was raised on grass pasture, all the fossil fuels expended are the shipping and the cooking; not really all that much. All other CO
2 is already ecologically balanced.
However, given the way we raise cattle a whole lot more CO
2 is consumed than need be.
So, it's not the chickens breathing that's the problem, but how we get grain into their gullets.
I think this answers your question?