How to measure, report and verify soil carbon change to realize the potential of soil carbon sequestration for atmospheric greenhouse gas removal

There is growing international interest in better managing soils to increase soil organic carbon content to contribute to climate change mitigation, to enhance resilience to climate change and to underpin food security, through initiatives such as international “4p1000” initiative and the FAO’s Global assessment of soil organic carbon sequestration potential (GSOCseq) programme. Since soil organic carbon content of soils cannot be easily measured, a key barrier to implementing programmes to increase soil organic carbon at large scale, is the need for credible and reliable measurement/monitoring, reporting and verification (MRV) mechanisms. Without such mechanisms, investments could be considered risky.

In this paper we review methods and challenges of measuring SOC change directly in soils, before examining some recent novel developments that show promise for quantifying SOC. We describe how repeat soil surveys are used to estimate territorial changes in SOC over time, and how long-term experiments and space-for-time-substitution sites can serve as sources of knowledge and can be used to testing models, and as potential benchmark sites in global frameworks to estimate SOC change. We briefly consider models that can be used to simulate and project change in SOC and examine the MRV frameworks for soil organic carbon change already in use in various countries / regions. In the final section, we bring together the various components described in this review, to describe a new vision for a global framework for MRV of soil organic carbon change, to support national and international initiatives seeking to effect change in the way we manage our soils.