Last August Stijn wrote a post titled The extreme cost-effectiveness of cell-based meat R&D about this subject.
Let me quote the bottom line (emphasis mine):
This means one euro extra funding spares 100 vertebrate land animals. Including captured and aquaculture fish (also fish used for fish meal for farm animals), the number becomes an order 10 higher: 1000 vertebrate animals saved per euro.
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Used as carbon offsetting, cell-based meat R&D has a price around 0,1 euro per ton CO2e averted.
In addition, as I wrote in a comment, I also did a back of the envelope guesstimate model to estimate the cost-effectiveness of donations to GFI, and arrived at $1.4 per ton CO2e (and $0.05-$5.42 for 90% CI).
It is important to mention that our methods are not nearly as thorough as the work done by Giving Green or Founders Pledge about climate change, and I wouldn’t take it too seriously. Nevertheless, I think that it at least hints the order of magnitude of the true numbers.
Edit: I just realized that Brian’s comment refers to a newer post by Stijn, which I assume reflects his broader opinions. However I think that the discussion in the comments on Stijn’s older post that I linked to is also interesting to read.
I just want to add, on top of Haydn’s comment to your comment, that:
You don’t need the treatment and the control group to be of the same size, so you could, for instance, randomize among the top 300 candidates.
In my experience, when there isn’t a clear metric for ordering, it is extremely hard to make clear judgements. Therefore, I think that in practice, it is very likely that let’s say places 100-200 in their ranking seem very similar.
I think that these two factors, combined with Haydn’s suggestion to take the top candidates and exclude them from the study, make it very reasonable, and of very low cost.