I don't know much about climate science, but won't plants multiply and grow faster until we eventually hit a new equilibrium CO2 level? I guess the only danger is reaching thermal runaway before that happens? Then again, earth CO2 levels have been far higher in the past without signs that it killed off much life on Earth. Is rising CO2 that dangerous? Don't humans already have effective ways to reduce surface heating…
It doesn't matter how much plants and algea grow, when they die, they send the carbon back into the atmosphere and ocean. We have to sequestrate the carbon and totally remove it from the ecosystem.
Sequestration is what took millions of years, when major events buried large swabs of living matter in the ground "forever".