Soil carbon tonne-year accounting: Crediting the additional time-integrated amount of carbon captured in soil

Abstract

Soil organic carbon (SOC) sequestration has become a critical component of climate change mitigation strategies, offering a natural and economically viable means to mitigate atmospheric CO2 levels. Current practices in SOC sequestration auditing face limitations due to the requirement for carbon permanence, which can discourage landholders from participating due to long-term commitments and uncertainties. We propose the concept of the Soil Carbon Tonne-Year as a new unit of measurement for assessing SOC sequestration, focusing on the time-integrated amount of carbon stored in the soil. Soil carbon tonne-year measures SOC stock across different operational soil carbon pools (such as Mineral Associated Organic Carbon and Particulate Organic Carbon), each with its own mean residence time. This approach, based on physical rather than economic or climatic metrics, aims to offer a more accurate, flexible, and realistic method of accounting for SOC. Our examples suggest that the Soil Carbon Tonne-Year approach could significantly enhance management flexibility, potentially increasing land value and leading to sustainable gains over the long term.