Over 2300 billion tonnes of carbon estimated in top soil, could help in climate change mitigation: Study

A new research has estimated more than 2,300 billion tonnes of inorganic carbon in minerals in the top two metres of soil worldwide, a finding that scientists say "underscores the urgency of incorporating inorganic carbon into climate change mitigation strategies." Inorganic carbon is found in ores and minerals, as opposed to organic carbon, which can be found in nature through plants and animals.

Researchers said that international initiatives aimed at increasing organic carbon content in soil - soil organic carbon (SOC) - should also consider the critical role of soil inorganic carbon (SIC) in achieving sustainable soil management and climate change mitigation.

Solid SIC, often calcium carbonate, tends to accumulate more in arid regions with infertile soils, which has led many to believe it is not important, they said.

However, SIC also plays a dual role in storing carbon and supporting ecosystem functions that depend on it, said the researchers, led by the Chinese Academy of Sciences (CAS).

Thus, they said, SIC can be an "additional lever" in maintaining and enhancing carbon sequestration, which refers to capturing carbon dioxide, either from the air or directly from the point of production, and storing it for long term. Carbon sequestration is considered a key method for removing carbon from the Earth's atmosphere.

While society has recognised the importance of soil to be fundamental to nature-based solutions for combating climate change, the major focus has been on the SOC. It is now clear that inorganic carbon deserves equal attention, the researchers said.

They said their SIC estimates of more than 2,300 billion tonnes are more than five times the carbon found in all of the world's vegetation put together, and that this could be key to understanding how carbon moves around the world.

"But here's the thing: This huge carbon pool is vulnerable to changes in the environment, especially soil acidification. Acids dissolve calcium carbonate and remove it either as carbon dioxide gas or directly into the water," said Huang Yuanyuan, professor, the Institute of Geographic Sciences, CAS, and co-lead author of the study published in the journal 'Science'.

"Many regions in countries like China and India are experiencing soil acidification due to industrial activities and intense farming. Without remedial actions and better soil practices, the world is likely to face a disturbance of SIC in the next thirty years," she said.

A disturbance of SIC can hamper plant growth by disrupting the soil's ability to counter acidity, regulate nutrients and stabilise organic carbon.