800,000 years is pretty slow, though. Maybe we could speed it up with the right conditions? I think what we'd need to replicate the azolla event is a large fr

800,000 years is pretty slow, though. Maybe we could speed it up with the right conditions? I think what we'd need to replicate the azolla event is a large fresh-water lake that's very still and stagnant, so that O2 levels in the deep parts are low enough that when the plant dies and sinks to the bottom it doesn't decompose. Or alternatively would could have azolla-harvesting ships that skim the surface, and then we could turn the resulting plant mass into biochar and bury it, or something like that. Azolla doesn't do well in salt water, but maybe we could engineer a salt-tolerant variant. The Black Sea, for instance, has about half the salinity of the rest of the ocean. For some salt-tolerant azolla variant to get loose and cover the whole ocean sounds like it could be a major ecological disaster though, even if it does draw down CO2 really fast. Azolla is sometimes used to feed livestock and as a fertilizer, so it could displace other, potentially more CO2 producing ways of accomplishing the same thing. I think there have been some efforts to use it as a food for humans.