Agricultural Soil Carbon: A Call for Improved Evidence of Climate Mitigation

We identify the critical need for causal approaches to be employed at the scale of commercial agriculture to build high-quality evidence for measurement, monitoring, reporting and verification (MMRV) to quantify the effectiveness of soil carbon farming. We emphasize that, contrary to arguments that have led to reliance on process-based biogeochemical models for carbon accounting, empirical measure-and-remeasure projects appear scientifically feasible at regional agricultural scales with current best practices for soil sampling and carbon analysis. Even if modeling approaches remain predominant, we make the case that project-scale empirical data are required to test, support and advance the ability of such scaling approaches to estimate real emission reductions and removals. To increase confidence that the effects of carbon farming represent real carbon accrual and/or avoided emissions, we summarize the design principles that should underpin measure-and-remeasure approaches. We use the term “carbon farming” in this report since change in soil organic carbon is the primary outcome variable in agricultural soil climate accounting and the term is being increasingly used in policy frameworks, such as the European Union’s certification for carbon removals (EU, 2024). However, we recognize that soil carbon accrual and avoided emissions are just one way that climate-smart and regenerative agricultural practices contribute to climate change mitigation, adaptation and sustainability. We do not address the effectiveness of soil carbon farming as a climate mitigation strategy, which necessitates quantification of potential tradeoffs with emissions of other greenhouse gases (GHGs) of concern such as N2O. Instead, we focus on the need to expand soil MMRV to validate that climate mitigation claims represent reality. We propose practical ways forward to generate high-quality evidence at the scale of commercial agriculture that can help to inform, quantify and validate GHG outcomes, as well as support and advance the suitability of the varied MMRV approaches being used or proposed for scaling soil carbon farming. We emphasize that such high-quality evidence can, more broadly, help to identify and improve practices that have the greatest benefits for climate adaptation and mitigation.