An Australia's worth of kelp farms in the deep ocean might do it too. Tricky parts are supplying the nitrogen fertilizer (upwelling might be enough), automatin

An Australia's worth of kelp farms in the deep ocean might do it too. Tricky parts are supplying the nitrogen fertilizer (upwelling might be enough), automating planting/harvesting (many drones on a wire probably) and fuel costs (offshore rig-based ideally). Sinking the kelp may keep the CO2 on the ocean floor long enough to do the trick, or sink packs of rotting kelp in kelp-plastic membranes for much longer. Bonus is this is all basically bio-fuel, so you're basically growing a renewable oil patch. Drawdown til targets are hit and then you can burn or eat the rest. Also bonus: dampens waves, so seastead potential. Recommended: attach simple motors to the anchored tethers, sinking kelp 30m down during storms or nearby ships to avoid big wave damage and the deepest hulls. Or keep it at that level for just slower growth.