Inducement of massive algea blooms is extremely cost effective, can store massive amounts of carbon very quickly, and horrendously damaging to large lake, and o

Inducement of massive algea blooms is extremely cost effective, can store massive amounts of carbon very quickly, and horrendously damaging to large lake, and ocean ecosystems, where you can use them. There are two problems, the first is that its only effective as storage if you make it damaging enough to ensure mostly anoxic decomposition, so the damage is required. Its reusable though, so if you waste a huge lake, there is no reason not to do this over and over again. The second problem is that if you do it in oceans, then ensuring it sinks to the bottom, becomes key, though this is straightforward if you do it on a scale to solve global warming in a single sweep. Though you would sacrifice an ocean and everyone living nearby for decades. The one time someone tried it, it was a far more massive success than anticipated, but also killed the fishing and tourism industry on several nearby, and not so nearby islands, for several years. A slower variant is to build artificial floating reefs, increasing the amount of marine snow. That improves the ecosystem, but requires significant investment.