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Comment by ryanjshaw | Hacker News Reader

> cows produce a disproportionate amount of methane, which is a disproportionately powerful greenhouse gas.

Can somebody explain run through these quickly, I'm not sure which parts are wrong and how much they're wrong:

1. the constituents in the methane came from the food the cows eat?

2. the food got it from the atmosphere?

3. cows don't increase methane constantly, rather it's the marginal volume of feed required to sustain every new cow on the planet less the ones slaughtered? I.e. the growth in new supply?

4. Eliminating cows raised for meat would stop the increase in methane due to increase in supply and it would result in a one-off net reduction in atmospheric methane in time proportional to what cows were releasing, assuming the food continues to grow?

5. What happens when the food the cows are no longer eating dies, does anything get released then?

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Not my field, so assumptions and simplifications follow. Animal feed mostly grows from absorbing carbon dioxide, not methane. Cows (and other grazing animals) produce net positive methane because their gut microbiota ferment the animal feed, producing methane. So, to keep methane in balance, something in the local grazing biome needs to absorb methane. Otherwise, cows can increase proportional atmospheric methane.

Well yes, but the same grass that these cows eat....would rot and release methane eventually anyway? Is that not correct?

Not quite correct - the grass may rot due to non-methanogenic organisms and/or be eaten by something.

It is correct.

Assuming no fossil fuels provide the carbon, the whole thing is indeed carbon neutral.

However, from a green house gas perspective, plants consume Co2 (moderate green house potential), and either due to rotting or as part of digestion, methane does get produced. Which has a high green house potential. Not in identical proportions to the co2 consumed of course, cows and rotting plants also produce co2.

So think of part of the problem being some co2 being converted into a more problematic green house gas (methane) with a lot of steps in the middle.

Also people being jealous of that tasty steak that is a byproduct of the process.

1/2: Grass turns CO2 and water into sugar and oxygen, cow eats grass and turns sugar and oxygen in to methane and CO2 and more cow.

(Via intermediary step of some of their stomachs being bioreactors filled with bacteria, oh the irony).

3: Sure, but demand is still going up: https://en.wikipedia.org/wiki/File:Beef_production_1961_2021...

4: I'm not sure I follow the question, but methane has an atmospheric lifetime of about 12 years, so it would probably fall, but I'm not sure how much by

5: Some mixture of CO2, methane, and carbon sequestration; at this scale it's worth considering which crops are grown and how they are used precisely to minimise that kind of impact

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