There is a water plant called Azolla that actually captured so much co2 long ago that many think it triggered an ice age. Why not incentivize natural carbon sequestration and just produce huge fields of this stuff everywhere? I would hope we find a fish that likes eating it, or find a way to convert it into other animal feed, if nothing else. I don't think carbon tax credits or whatever they are called are enough for someone to justify making an actual sequestration-only operation.