Maintaining things sitting in the ocean is still expensive. You can’t send robots out, you must send humans.
Oil rigs are worthwhile just because they can be turned on/off relatively easily depending on market conditions and when they are on, they mint so much money that expensive humans are a rounding error.
Why can't you send robots out?
That might disturb the ocean ecosystem.
And these trees don't?
I think the larger point is that there isn't a simple, obvious, "Why don't we just do XYZ?" solution to the problems being discussed here.
I agree anything we do at scale will affect the ecosystem. However, restoring an ecosystem to a previous state seems less risky than changing oceans to a new state.
There are plans to add (I believe) iron oxide to the oceans to increase algae growth. Don't recall the organization's name right now.
I hope not. You can permanently alter (i.e. for decades) the climate in a region by creating an algae bloom.