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Comment by ramblenode | Hacker News Reader

You make a good point about animal-based carbon emissions being a closed loop, but I don't think your conclusion that this loop doesn't accelerate the greenhouse effect is correct.

Methane degrades to C02 in 1-1 proportion. So at any time, if more atmospheric carbon is concentrated as methane than as C02 then the greenhouse effect will be stronger at that time (because methane is a stronger GHG). If agriculture removes 1 unit of C02 from the atmosphere (from feedstock) and emits 1 unit of methane (from cow) then total atmospheric carbon is unchanged but the proportion of methane, and therefore the total GHG effect, is increased at that time. Summing over time, and you get an increase in overall heat that has been trapped.

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> I don't think your conclusion that this loop doesn't accelerate the greenhouse effect is correct

It's not like mammalian herbivores are a recent invention. If a constant amount of mammalian herbivores in the world would cause a constant acceleration of greenhouse effect then the greenhouse effect would have increased exponentially for millions of years already. That has not been the case.

If you increase the number of mammalian herbivores in the world then the greenhouse effect will increase for about a decade because of increasing levels of methane. After a decade, the methane level (and therefore the greenhouse effect) will have found a new (higher) equilibrium and no longer increase.

It's not new, but the number has hardly stayed constant, since at some point humanity started mass herding.

And, also, we kinda quadrupled the cheptel size in 50 years ? https://ourworldindata.org/meat-production#global-meat-produ...

(To be fair, I was expecting more, and I was again astonished by the relative numbers of cattle vs poultry)

We have increased farming, but the American plains were there once home to vast herds of bison. Basically there’s been 30 million large ungulates there for a very long time.

There are roughly 1.5 billion cows in the world right now.

https://cairncrestfarm.com/blog/how-many-cows-are-there-in-t...

Yeah... And we hunted that population to... ?

Humans and their livestock make up the vast majority of the mamallian biomass.

The natural carrying population of bison eating grass is going to be considerably smaller than cows being fed grains produced using artificial fertilizer and major irrigation projects, given antibiotics to grow larger, etc. Part of what makes American beef so carbon intensive is that massive supply chain moving around animals and feed.

Another thing to consider is that American beef cattle are famously rich methane sources due to the artificial diet they’re fed and how early calves are started on corn. Not only are there fewer bison, they would be smaller and eating the food they evolved to eat so each of those animals would be smaller and less gassy.

> It's not like mammalian herbivores are a recent invention. If a constant amount of mammalian herbivores in the world would cause a constant acceleration of greenhouse effect then the greenhouse effect would have increased exponentially for millions of years already.

Factory style livestock farming is a recent invention. There's no way a similar amount of herbivores existed a million years ago in the wild compared to what we can currently cage and feed corn product to.

You're missing the point. An increase in the number of mammalian herbivores just means an increased point of equilibrium for methane. But there will still be an equilibrium.

In contrast, using fossile sources of carbon (oil etc) will increase the greenhouse effect every year even if the usage is constant.

And you seem to be missing the point that increasing the equilibrium concentration of atmospheric methane is something we very much do not want to do. And that agriculture isn't actually a closed loop.

> then total atmospheric carbon is unchanged but the proportion of methane, and therefore the total GHG effect, is increased at that time. Summing over time, and you get an increase in overall heat that has been trapped

This is not correct. We are already in a steady state. Methane levels due to cattle are already at their maximum (given a fixed amount of cattle).

At any point in time, gras will absorb some CO2 from the atmosphere, cattle will convert some gras / carbon into methane and emit the latter into the atmosphere, and some methane in the atmosphere will decompose into CO2. This is a continuous process, that's happening every second, and if the amount of cattle is kept constant, there is a maximum amount of methane that you can reach in the atmosphere as well as a maximum amount of CO2. After all, the total amount of carbon involved in the process is constant – energy conservation dictates that mass doesn't appear out of nowhere.

In fact, since we've been doing agriculture for a time much longer than the time scale in which grass grows, a cow digests grass or methane decomposes into CO2, this whole closed loop has already settled into a steady state: At any point in time, the amounts of methane and CO2 in the atmosphere due to cattle are constant. The resulting radiative forcing will thus stay constant, too.

Maybe we were talking past each other.

> ...and if the amount of cattle is kept constant...

My point (unclear) is that this is not a constant, but a variable (in the sense that it is a societal choice). Animal agriculture shifts more of the distribution of atmospheric carbon at any time toward methane, which accelerates warming.

> ...this whole closed loop has already settled into a steady state: At any point in time, the amounts of methane and CO2 in the atmosphere due to cattle are constant.

The premise that the amount of animal agriculture is constant is incorrect. It has been increasing year over year for some time as the human population increases. The theoretical concentration of methane has been increasing over that same time. It's also worth noting that industrial animal agriculture is not a closed loop because it currently relies on mined hydrocarbons for feedstock fertilizer and transport.

Thanks for your comment!

> The premise that the amount of animal agriculture is constant is incorrect.

That certainly is true – I just had a look at the exact numbers: Cattle has seen a 15.6% increase between 2000 and 2020[0]. However, even if you double the numbers in my calculation in my other comment[1], you will see that agricultural greenhouse gases in the atmosphere are still basically nothing compared to those caused by fossil emissions.

> because it currently relies on mined hydrocarbons for feedstock fertilizer and transport.

Many types of food require fertilizer for production and logistics. I'm not trying to say that animal agriculture might not be comparatively bad here but we certainly won't get rid of fertilizer- and logistics-related emissions over night by overcoming animal agriculture. In fact, it could be that we'd just replace one emission source with another. So, before prescribing vegan diets for everyone, I'd really like to see some numbers that suggest that such a move would actually change anything.

[0]: https://www.destatis.de/EN/Themes/Countries-Regions/Internat...

[1]: https://news.ycombinator.com/item?id=35675049

> Methane degrades to C02 in 1-1 proportion

Source? I understood that the long-term radiative forcing of methane was lower than CO2, which is incompatible with this claim.

Presumably, each molecule of atmospheric methane (CH4) primarily degrades through oxidation to 1 CO2 and 2x H2O - this is basic chemestry.

Although atmospheric losses to space and capture into oceans and subsequent precipitation into hydrates cannot be excluded as potential atmospheric methane sinks, I expect those to be only marginal at the grand scheme of things.

> Although atmospheric losses to space […], I expect those to be only marginal at the grand scheme of things.

Indeed: https://en.m.wikipedia.org/wiki/Atmospheric_escape#Earth

The source there would be that they both contain only one carbon atom...

The four hydrogen atoms then... oxidize to form water?

Eh, we use plenty of petroleum based fertilizer to grow animal feed, so it is still there.

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