I think we need to go a step further. The article I linked earlier touches on how several natural carbon sequestration systems rerelease carbon seasonally or have other implications. Seagrasses release carbon when water is warmer than usual. Trees release carbon during forest fires or from natural decomposition, and even potentially cause local atmospheric warming due to a low reflectivity. Artificial methods of sequestration are necessary, whether as systems that directly capture atmospheric carbon and store it or as systems that interrupt the process of natural decomposition or combustion and divert it to storage or further processing.