Could you explain which externality this is? I know they produce a lot of methane which is more of a GHG than CO2, but as far as I know, that methane is a part of the carbon cycle so it should be a net neutral contribution.
The problem isn't the cycle, it's the delta of total emissions in the cycle. By your definition, literally everything is part of the carbon cycle, as we are just putting the carbon of old plants in the air, which will slowly be consumed by plants. The problem is if we put all that carbon in the air all at once, we have problems.
The biomass of livestock is 14x larger than all other mammal apart from humans[1], so it makes sense that, even if their carbon cycles is short, it's still a massive amount of effectively permanent GHG that exists in our atmosphere that wouldn't otherwise be there... about 15% of all emissions[2].
Not counting livestock as emissions because they form a decades long closed loop could be fine when we are carbon negative, but we are dealing with the very real problem of total emissions right now, not just unsustainable growth of emissions.
I think a big part of it is that we have so many more cattle than the earth could naturally support, and the number is only increasing as the world gets more developed. As it stands, even without any other sources of carbon emissions cattle would be enough to cause significant climate change on their own. [0]
I don't know if it's by gross weight or calories, but the number I've heard is that feeding plants to animals is 10-20 less effective than just having people eat the plants. Or mostly eat the plants. So, in the case of Denmark, where 50% of the surface area is used to grow food for pigs, we could instead use 3-5% of the surface are to grow food for people and come out at something resembling the same amount of food, at least if we're just talking "food needed to survive". And given some of the other talk we see on this site, (or used to see a few years ago) about how indoor farming is an absolute necessity because we're running out of land due to rising populations, I think that seems quite significant.
BTW, I am not a full-time vegan nor interested in becoming one, but the average meat consumption in Denmark is as far as I know measure in the hundreds of grams per day. Maybe there's room for compromise?
Cows don't eat plants that people can derive appropriate nutrition from. They also don't generally use land that is appropriate for crops. Also, from what I understand, the emissions from the animals isn't significantly different than seasonal die off from natural grasslands they graze on. Beyond this, most of the calculated water consumption "used" is rainwater on said grasslands.
Cows in America derive most of their calories from corn. And while most Montana cows generally live on land unsuitable for crops, Montana only has a small fraction of American cows.
And I believe that your comments are even less true in other prominent cattle producing countries than America.
I'm not a climate scientist, presumably the Danish government has consulted some of those though. My understanding is that livestock farming, in particularly beef and dairy cows, contribute significantly to the Co2e(carbon dioxide equivalent) emissions of the farming sector, which itself is a major overall contributor. The negative externality is this emission, which is not accounted for in the price of beef and dairy products
Given a constant population of cows [1], the cows do not cause an increase in green houses gasses over time.
This is because the methane from the cows has a half life of between six and eight years [2]. Given a fixed population cows, the amount of GHG going into the atmosphere is the same as the amount of GHG coming out of the atmosphere.
The problem with run away climate change is oil. Given a fixed consumption of oil, the amount of GHG in the atmosphere increases over time.
perhaps some kind of financial incentive to curb and eventually reverse the artificially inflated population of cows whose emissions, while part of the closed carbon cycle, increase the greenhouse gas effect of our atmosphere during their half lives, would be a simple and effective step we could take towards increasing the odds we survive the next few centuries that is not at all at odds with also tackling our reliance on fossil fuels?
This is a factual matter. Why be snarky when you can instead lookup the answer? The population of cows in the EU has been relatively constant with a slight downward trend. [1]
Maybe I’m using the wrong term but my understanding is that the carbon comes from the feed, which itself pulls it from the atmosphere. Thus, it came from the air, and goes back into the air.
The fossil fuels did the same but on a grander scale and longer timeline where the carbon becomes sequestered. Carbon taxes on that make sense.
From what I understand carbon comes from the soil as well as from the air, and it's supposed to be "stored" back into the soil by various means but our agriculture and more generally human activities tend to accelerate release of carbon from the soil and refrein the storing process. And that provokes a climate disimbalance.
There was a good video on the relation between carbon cycle and massive extinctions throuhout history (1h long) : https://www.youtube.com/watch?v=uxTO2w0fbB4
It has a short half-life (years) in the atmosphere though, while CO2 has a very long half-life (centuries or more). Methane in the atmosphere gets photochemically oxidized into CO2 and H2O, but more slowly than when it's combusted.
> I don't really know what you mean by it being part of carbon cycle
Plants breath in co2 from the atmosphere and bind the carbon in their structure. Cows eat the plants and turn some percentage of the bound carbon into cow meat, the rest they poop or fart or breath out. Eventually all that carbon ends up back in the atmosphere where plants again can bind it. This is the carbon cycle. Thus the point is that cows existing do not increase the carbon in circulation. (As opposed to digging up coal or drilling for oil/gas which liberates carbon which used to be in circulation but become bound in fossils.)
The biomass of livestock is 14x larger than all other mammal apart from humans[1], so it makes sense that, even if their carbon cycles is short, it's still a massive amount of effectively permanent GHG that exists in our atmosphere that wouldn't otherwise be there... about 15% of all emissions[2].
Not counting livestock as emissions because they form a decades long closed loop could be fine when we are carbon negative, but we are dealing with the very real problem of total emissions right now, not just unsustainable growth of emissions.
1: https://www.pnas.org/doi/10.1073/pnas.1711842115
2: https://www.ucdavis.edu/food/news/making-cattle-more-sustain...