Is soil carbon a viable carbon removal solution?
· 5 min read
Last month, the EU carbon removal expert group had a meeting discussing carbon farming, including increasing the stock of carbon in soils with the purpose to find methodologies to certify. It does not seem to be a well-known fact that there is no scientific consensus if commonly used methods used to store more carbon in soils actually work. Here, I am talking about regenerative agriculture. Biochar also technically stores carbon in the soil. There are also new ways to store inorganic carbon in soils, but these are separate methods from what is discussed in this post.
There have been a number of publications in the last couple of years calling the effectiveness of the soil carbon building methods and our knowledge of them into question.
The Environmental Defense Fund State of the Science report from 2022 found a "lack of consensus about the degree to which agricultural soils can be managed to sequester sufficient carbon dioxide to have an appreciable impact in mitigating climate change". They concluded that "Sequestering soil carbon remains an uncertain approach to climate change mitigation"[1].
Similarly, World Resource Institute researchers have found that ” [soil carbon practices] tend to have limited documentation and analysis of the feasibility of the massive expansion of practices they are relying on to sequester carbon. They also rely largely on practices that decrease crop production or on practices on working lands that more recent science has shown to be ineffective or less effective at sequestering soil carbon, such as no-till farming." [2].
For example, while topsoil carbon sequestration might seem promising at first glance for methods such as cover crops and no-till, studies that have considered soil carbon content at depths below the topsoil have shown an offset in the carbon sequestered in the topsoil by a decrease in deeper layers[3,4,5,6].
The EDF report and WRI explainer mentioned above are great overviews, highlighting the uncertainties of this. Moreover, a 2022 article suggests that "most of the management practices associated with regenerative agriculture are not likely to lead to a large net sequestration of organic carbon in soils"[7]. Adding to this, a recent review from 2023 outlines the lack of consensus on the mechanisms leading to carbon storage and addresses controversies related to agricultural and forestry management practices for soil carbon accumulation[8].
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