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Comment by ageofwant | Hacker News Reader

Fertilisers and fuel did not come from the air. There are hundreds of millions of cows (and other livestock) that did not exist before. Landscapes have been sterilised to support them with a massive resulting freeing of previously captured carbon, or carbon trapped in a slow cycle. Methane from ruminants are a significant source of CO2 and are not easily recaptured, not to mention a potent greenhouse gas.

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Carbon dioxide is captured from the air, by plants, and then eaten by cows. So you're saying that any greenhouse gas from cows is that which has been previously captured.

But you're missing the fact that some of the CO2 captured by the grass is farted by the cows as methane, CH4.

About 1% of the CO2 is released as CH4.

CH4 is about 25 times more potent as a greenhouse gas. It's one of the most potent greenhouse gases.

Luckily methane has a half life of 7 years in the atmosphere, so anything we do to reduce methane emissions is likely to be helpful.

"Fertilisers and fuel did not come from the air."

True, and they are probably at least a small net flow into the atmosphere. But:

"There are hundreds of millions of cows (and other livestock) that did not exist before."

... that part doesn't matter: agriculture is by nature carbon-neutral (except if you count mechanization aspects like fertilizers + fuel).

Agriculture is most certainly not carbon-neutral by nature, even with your exclusions. CH4 is persistent and not readily available for photosynthesis.

It burns back into CO2 before too long.

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