能源、气候与材料2021journals.plos.org
红海藻补充剂使肉牛肠道甲烷排放降低80%以上
Red seaweed supplementation reduces enteric methane by over 80% in beef steers
进阶 · 约 30 分钟读完前置知识：反刍动物营养、肠道微生物与甲烷生成、温室气体核算
导读
这篇 PLOS ONE 研究测试在肉牛日粮中添加红海藻的效果，报告肠道甲烷排放降低超过 80%。它属于寻找可规模化降低反刍动物甲烷排放的饲料添加剂研究，但实际牧场应用和净气候效益仍有争议。
HN 关注点：牛甲烷与气候的关系：红海藻看似高效，但评论围绕碳循环、牧场可行性、缺少基线对照以及减少牛肉消费展开争论。
后来怎么样
该研究成为红海藻作为反刍动物甲烷抑制剂的关键概念验证，推动了后续重复试验和商业开发；但放牧牛投喂、长期有效性等问题未解决，尚未成为牧场标准做法。
HN 评论精选
这几条评论里：质疑 4
质疑牛甲烷属于生物碳循环，不应与化石碳排放混为一谈，相关讨论可能转移真正的气候问题。
这个话题出现时我常看到一个误解：没有区分碳循环和单向碳排放。你呼出二氧化碳，但这些碳来自你吃的食物，而食物又从大气获得碳，所以是循环；忽略运输、毁林等，这个系统实际上碳中和。相反，挖石油并燃烧没有循环，是单向的。牛的甲烷生产是稍复杂的碳循环例子：牛产生甲烷，它比二氧化碳温室效应更强，但会在大气中降解为二氧化碳；由于这些碳来自牛吃的饲料，又是循环。牛释放的甲烷不断降解，不会持续累积，大气中牛甲烷总量最终取决于牛群规模，或更准确地说饲料消耗量。牛群规模长期相对稳定，而且地球上曾有大量野生反刍动物。因此我认为这个话题常分散人们对气候问题根源的注意力。
Doji查看英文原文
A common misconception which I frequently see when this topic arises is the failure to distinguish carbon cycles and one-way carbon emission. You exhale carbon dioxide. However, this carbon dioxide comes from the carbon in the food you eat, and the food you eat obtained it from the atmosphere. Thus, it's a cycle. As a system (ignoring food transportation, deforestation, etc.) it's effectively carbon neutral. By contrast, when we dig up oil and burn it, there is no cycle. It's a one way street. Methane production from cattle is slightly more complicated instance of a carbon cycle. The cows produce methane, which is a more potent greenhouse gas than carbon dioxide. However, it degrades in the atmosphere into C02. Since this C02 was obtained from the food the cattle ate, this is another cycle. Since the methane released from cattle is continually degrading, it does not accumulate. The total amount of bovine methane resident in the atmosphere is ultimately a function of herd size, or perhaps more accurately quantity of feed consumed. You may be surprised to learn that cattle herd size has remained relatively stable over time. Additionally our planet was once host to wild ruminants like Buffalo which no longer exist in large numbers. As a result I would be very surprised to learn that bovine methane production is completely out of historical context. As a result I see this as a topic which generally serves to distract from the root cause and real problem associated with climate change - fossil fuel usage.
质疑红海藻方案适用场景有限、难以用于放牧牛，且牛微生物组可能产生适应性。
《连线》有篇文章解释为什么藻类并非营销所说的万能解药：它基本上只对放牧牛有用（大豆和玉米饲养的集中饲养牛本来甲烷就少得多），而且没有实际办法把藻类加入放牧牛的日粮。他们还推测牛的微生物组会适应藻类。
headbee查看英文原文
Article from Wired on why algae isn't the silver bullet it's marketed as: https://www.wired.com/story/carbon-neutral-cows-algae/ Essentially, it's only useful for pasture raised cows (soy and corn fed feedlot cows already produce a fraction of the methane) and there's no practical way to add algae to pasture raised cows' diets. They also speculate that cows' microbiomes will adapt to the algae.
质疑研究缺少“无牛”基线，草料自然腐烂本身也产甲烷，减排效果可能被高估。
我觉得大家都漏掉了一个非常重要的点：牛吃的草如果只是留在那里腐烂，也会产生同样多的甲烷。并不是牛把本来会变成尘土的东西变出了甲烷。这些研究都没有考虑这一点，只测量进入牛和从牛出来的东西，却没人考虑同样饲料在没有牛参与时会产多少甲烷。
gambiting查看英文原文
There is an incredibly important part of this that I feel everyone is missing. The grass eaten by the cows would produce exactly as much methane if it was just left to rot. It's not as if cows somehow produce methane out of grass that would otherwise just....turn into dust? None of those studies take this into account, they all just measure what comes into a cow and what comes out, but no one takes into account the amount of methane produced from the same feed even without cows involved. https://www.cbc.ca/radio/quirks/mar-2-2019-the-goodness-paradox-secrets-in-poop-converting-carbon-to-coal-and-more-1.5037008/do-cows-produce-more-methane-than-rotting-grass-1.5037019
质疑最直接的减排方式是减少牛肉和牛奶消费，而不是依赖技术方案。
不吃牛、不喝牛奶，就能把你与牛相关的碳排放减少 100%。你其实不需要技术或创业公司来解决这个问题！
valgor查看英文原文
Not eating cows or drinking cow milk reduces your carbon emissions from cows 100%. You actually don't need technology or a start up to solve this issue!
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从这篇论文所有 HN 讨论帖的全部评论里整理出来的链接。
历次讨论
- 2021Hacker News 讨论帖269 分 · 289 评
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