Thoughts on Lal 2008, “Carbon Sequestration.”

From Phil. Trans. R. Soc. B

Carbon sequestration is defined as the transfer of carbon from the atmospheric carbon pool to other carbon pools. Including the atmospheric pool, there are five carbon pools, with the largest being the oceanic pool at an estimated 38,000 Pg C. The pedologic pool is the third largest at 2500 Pg and further subdivides into the soil organic carbon (SOC) and soil inorganic carbon (SIC) pools.

There are abiotic techniques for carbon sequestration comprised of engineering methods and chemical processes. Many of them consist of injecting carbon into non-atmospheric pools. There are also biotic techniques that rely on organisms, primarily plants and microbiota, for removing CO2 from the atmosphere. Theoretically, abiotic techniques can store more carbon, but there are questions about the safety and reliability of those techniques. The risk of carbon leakage and the effects of leakage on ecosystems is still uncertain. Additionally, the expensive cost of geo-engineering is a limitation. By comparison, biotic techniques are more cost-effective and less risky, while providing accompanying benefits such as improved soil and water quality and ecosystem preservation absent from abiotic methods. Biotic approaches do have a smaller cumulative carbon sink capacity than abiotic approaches.

Biotic techniques can be subdivided into oceanic sequestration and terrestrial sequestration methods. In terms of terrestrial methods, afforestation in the U.S alone can sink up to 117 Tg C per year in the U.S alone (IPCC 1999). The cost of afforestation is the drain on water resources, which can make the practice prohibitive in drought-stricken regions, like California. The family of techniques focusing on SOC and SIC sequestration can also cumulatively sink a significant amount of carbon. Land use conversion and restoration of degraded soils can increase overall microbiota concentrations and diversity in soils. Restoration of degraded soils and habitats in the tropics can potentially sequester an additional 1.1 Pg C per year (Grainger 1995). What constitutes “degraded lands … with potential for afforestation and soil quality enhancement” is something I am not clear on, as I have not read the Grainger paper. Moving away from mono to multi-cultures for agricultural crops can mitigate SOC losses and improve the ability of agricultural-use land to sequester carbon.

A lingering question — how many acres could be converted from agricultural usages and how much soil could be restored if food waste were more controlled throughout the world?

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