Non-equivalent carbon crediting across agricultural land management protocols

Voluntary markets for agricultural carbon credits are expanding, promoting climate-smart practices purported to increase soil carbon and reduce greenhouse gas emissions. To contribute effectively to climate mitigation, markets must deliver credits that meet international standards guaranteeing credits are additional, conservative, and equivalent to at least one tonne of CO ₂ . Yet protocols for quantifying credits make different assumptions, raising questions about whether protocols meet the “equivalency standard”. We test for equivalency using a common dataset of 4,988 US Midwestern corn-soybean fields, representing a carbon market project, to estimate credit issuances for adoption of no-till and cover cropping practices. We find issuances, across the three major protocols being used for US croplands, differing for this common project by up to ~ 130,000 credits per year. Our “Protocol Intercomparison Project” reveals how quantitative evaluations can identify assumptions generating marked differences in crediting, thereby guiding research that informs protocol revisions to build confidence in mitigation.