Cation trapping by biochar reduces carbon removal efficiency

Biochar may be a scalable and cost-effective means of atmospheric carbon dioxide removal. However, frameworks for quantifying the effectiveness of this carbon removal pathway are still under development. Here, we quantify an initial carbon dioxide removal inefficiency associated with biochar's inherent ability to lock away cations and nitrogen that would otherwise be released back into the environment. Our analysis shows that this decreased flux of cations to soil water systems associated with the formation of biochar leads to a broad range of carbon dioxide removal inefficiency, anywhere from having no impact up to ~40% inefficiency. We argue that biochar's inherent ability to sequester cations and nitrogen and linked changes in carbon fluxes will need to be incorporated into monitoring, reporting, and verification frameworks when biochar is being sold as a means of durable carbon removal.