It's because the seaweed contains bromoform, which inhibits methanogenic reactions in bacteria:

https://www.discovermagazine.com/environment/feeding-seaweed...

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5270371/

https://en.wikipedia.org/wiki/Bromoform

It would be easier to add small quantities of industrially produced bromoform to cattle feed than to cultivate enough seaweed to get the same effects. However, the sort of producers who cater to environmentally conscious meat consumers may want to be able to tout "seaweed dietary additive" rather than "bromoform dietary additive" in packaging and promotional material.

Also there may be regulatory barriers to adding pure bromoform. AFAIK there are few regulations on introducing new plants into cows' diet, but pure chemicals may be regulated. Even if the only reason to add certain plants is to add chemicals into their diet.

> It would be easier to add small quantities of industrially produced bromoform to cattle feed than to cultivate enough seaweed to get the same effects.

If I recall correctly there are two issues with that a) bromoform itself is a GHG, you don't want to create more of it that gets released into the environment and use natural sources instead b) the researchers tried this and at least simple additives didn't have the same effect, perhaps it has something to do with how it gets released during digestion

If you had a link confirming B, I would be interested. To the first point: more bromoform will also be released in the environment if we deliberately cultivate large quantities of the kelp that produce it. A quick search doesn't show it as a greenhouse gas. It can deplete stratospheric ozone, but it is very short lived in the atmosphere.

https://sci-hub.tw/10.1071/AN15576 page 6 They're citing prior research showing declining efficiency of bromochloromethane additives "due to ruminal flow" while not observing that in their research using seaweed. But it's a bit of an apples to oranges comparison since one was an in vivo and the other an in vitro study. So I may have overstated the impact.

> A quick search doesn't show it as a greenhouse gas. It can deplete stratospheric ozone, but it is very short lived in the atmosphere.

Looks like you're right, I must have confused it with some other bromide.

Simple compared to getting people to change their eating habits, for sure.

“Maybe instead...” yes, the researches who came up with this are doing that, it’s their job.

changing people's eating habits in the west is super easy: tax undesirable products. price rises, demand drops. this also notably applies to everything else, e.g. gas/diesel, sugar, plastic.

just stop subsidizing beef. people will shift to chicken and pork/ham.

Compared to current amounts of cultivation, that sounds like a lot, but that is only the seaweed that humans consume.

Mass-scale seaweed production has been thrown around as a method for sequestering CO2.

Methane itself could be sequestered as well.

Either way, I'm fine with a beef tax to cover some of those costs, but lower-income groups might. I'm not keen on forcing an inferior diet on them.

I still wonder about cap and trade on meat, each human gets X steaks per year but they can sell their steaks on an exchange. Having the quota separate from the price would be about help people who don’t have much money quite a bit. It would also lead to higher meat quality; what would the point of buying McDonalds with a piece of your quota worth fifty bucks.

You can avoid eating beef without being "forced" an "inferior diet". In fact it would probably be better for people to NOT eat beef.

It is inferior by my standards, not yours. Your standards do not matter when it comes to my diet, and vice versa.

I am not forcing my standards on lower income people anyway, but supporting a tax that hurts them and not me seems wrong.