Or, direct air carbon capture. Getting to net zero would cost ~ $1 / gallon of gasoline (and equivalent for other things that emit.) I think we should be paying ~ twice that, minimum.
It's far less risky than trying to block out the sun.
Growing massive amounts of seaweed near the ocean top and then sink it into deep waters?
Seaweed mostly floats. Dead seaweed gets degraded by bacteria (just like everything else) and the carbon returns to the atmosphere.
Unless you would create a elevator that takes it down to the sea floor..