Evaluating Methods to Account for Soil Organic Carbon Stock Changes in Agricultural Lands

Abstract

Soil organic carbon (SOC) sequestration has essential implications for climate change mitigation, land health, and sustainable community development. However, land management strategies that encourage SOC sequestration are often underprioritized in carbon offset programs. We hypothesize that this is due to difficulties regarding accounting for soil carbon stock changes in response to land management choices. Field measurements are expensive and not often accessible to those in non-Annex I countries. Therefore, estimation methods using empirical or mathematical models are often utilized, but there are large discrepancies in estimates of changes in SOC stocks when applying different methodologies. We first focused on two of the estimation methods set out in the Intergovernmental Panel on Climate Change (IPCC) Tiered accounting approach in order to understand how well they performed against observed SOC changes in two U.S. field studies. This was accomplished by applying the tiered methodologies (Tier 1 & 3) to two published studies in the United States. Tier 3 was represented by the process-based models: COMET Farm and COMET Planner. We hypothesized that COMET Farm would produce estimates closest to the observed field measurements. However, we found that Tier 1 performed just as well as COMET Farm. To assure that land management strategies are being taken to sequester SOC, IPCC Tier 1 estimation methodology use should not be discouraged in situations where resources or land information is sparse. Next, we surveyed past and present participants in the Clean Development Mechanism (CDM) and Climate, Community and Biodiversity/Verified Carbon Standard (CCB/VCS) restoration and carbon offset programs to understand their approach for accounting for changes in soil carbon stocks. The survey invitations revealed communication issues between project leaders and developers. Several email invites came back with error messages stating that those addresses were no longer in existence. Therefore, we believe that this may lead to issues with project verification. This also suggests that collaboration is not occurring between projects. Finally, based on survey responses that were collected, soil carbon sequestration accounting does not seem to be prioritized in the CDM or the CCB/VCS. More research should be done to understand this prioritization given to accounting for soil carbon sequestration in carbon offset programs