Stock change accounting overestimates the potential climate benefit of soil carbon storage

Authors: Alexander, Jonathan; Gamble, Joshua; Venterea, Rodney - Rod

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2024
Publication Date: 3/4/2024
Citation: Alexander, J.R., Gamble, J.D., Venterea, R.T. 2024. Stock change accounting overestimates the potential climate benefit of soil carbon storage. Soil Science Society of America Journal. 88:745–752. https://doi.org/10.1002/saj2.20643.
DOI: https://doi.org/10.1002/saj2.20643

Interpretive Summary: Soil carbon (C) storage is being proposed to mitigate the effects of climate change. Because soil C can be re-released to the atmosphere as carbon dioxide (CO2), its storage in soils is considered temporary. This contrasts with atmospheric CO2, which has an extended lifetime and cumulative warming impacts. This means that the relative climate benefit of soil C storage depends on the amount of time that C is held out of the atmosphere. When we assess the total greenhouse gas (GHG) impact of agricultural land management, we often aggregate soil C storage with non-CO2 (nitrous-oxide and methane) emissions after converting all components to CO2 equivalents. However, this analysis does not consider potential re-emission of soil C or apply assumptions consistent with the timeframes of climate mitigation. This paper introduces and provides examples of a tonne-year accounting approach that can be used to reconcile differences in the context and timeframes of soil C sequestration and non-CO2 GHG emissions. The approach can be applied to commonly observed cropping systems data to estimate climate impacts associated with agricultural land management over given time horizons and with more clearly defined assumptions.

Technical Abstract: Agriculture is being called upon to store carbon (C) in soils to mitigate the effects of climate change. The soil C reservoir is considered part of the exogenic cycle or the fast C domain, meaning that it can be re-released in relatively short timeframes. This turnover means that soil C storage is considered temporary, and that its relative climate benefit depends on the time that C is held out of the atmosphere. This contrasts with atmospheric carbon-dioxide (CO2), which has an extended lifetime and cumulative warming impacts. When assessing the total greenhouse gas (GHG) impact of agricultural land management, soil C storage is often aggregated with non-CO2 (N2O and CH4) emissions after converting all components to CO2 equivalents (CO2e). However, such analyses may not consider potential re-emission of soil C or apply consistent assumptions. This paper introduces and provides examples of a tonne-year accounting approach that can be used to reconcile differences in the context and timeframes of soil C sequestration and non-CO2 GHG emissions. The approach can be applied to commonly observed cropping systems data to estimate climate impacts associated with agricultural land management over given time horizons (THs) and with more clearly defined assumptions.