Ruminating on the science of carbon ranching

1. There is interest in reducing CO2 concentrations in the atmosphere by managing livestock grazing to increase carbon (C) storage in soil. However, our understanding of the value of this practice of ' C ranching' is based on studies suffering substantial, overlooked methodological problems. 2. We reviewed research into effects of grazing treatments on soil organic carbon (SOC) stocks (mass SOC x area(-1)). We show the empirical basis for C ranching (C offset) projects relies mainly on studies with unrealistic and overly simplistic livestock grazing treatments (e.g. grazed vs. not grazed), suboptimal experimental designs (e. g. lack pretreatment data, low number of treatment replications) and problematic SOC stock metrics. 3. Synthesis and applications. It is not clear that grazing treatments differ enough in their effects on soil organic carbon (SOC) stocks to reliably offset CO2 generated by human activities and/or reduce CO2 concentrations in the atmosphere. Therefore, we caution against overselling the value of carbon (C) ranching. Knowledge of C ranching effects on SOC is inadequate to justify C offset projects that provide ranchers with payment for environmental services. To better quantify benefits of C ranching, we advise using current best practices and expanding C ranching research with more realistic treatments over either broader spatio-temporal scales and/or climate change treatments (e.g. drought, warming, elevated CO2).