Trillions of Tons of Carbon Are Missing From Climate Models

Not ideal.

• While the world’s soils are home to lots of organic carbon—such as leaf litter and animal waste—inorganic carbon, which is often in the form of solid carbonates, can also leak into the atmosphere. And it isn’t accounted for by current climate models.
• A new study focuses on the role of soils as both a storage for and emitter of carbon, and found that 23 billion tonnes of inorganic carbon could escape soil over the next 30 years.
• Good land management—as well as other practices, such as afforestation and improved rock weathering—can help slow down this significant source of CO₂.

The sole focus of people and programs combating climate change is finding ways to keep carbon out of the atmosphere. Planting trees is a big help, as their woody roots lock away carbon for decades, and companies are hard at work trying to find artificial means of sucking greenhouse gasses from the air and sequestering it underground. But in this obsession with tracking CO₂ levels, one significant source of both emission and storage has been overlooked—the soil.

According to a new study by the Chinese Academy of Sciences and Australia’s Commonwealth Scientific and Industrial Research Organization, the top two meters of soil beneath our feet currently hold roughly 2.3 trillion tonnes of inorganic carbon—five times more than all of the terrestrial plants on Earth combined.

Scientists arrived at this number by analyzing 200,000 soil samples from around the world, and found that concentrations of inorganic carbon were higher in arid and semi-arid landscapes where water is less likely to carry away these carbonates. While countries like Australia are particularly filled with inorganic carbon—the continent is the fifth largest repository, according to the study—its also found in wetter regions along rivers and around lakes and coastal areas. So, these carbon-locking soils impact the entire world. The results of the study were published last week in the journal Science.

“This huge pool of carbon is affected by changes in the environment, especially soil acidification. Acids dissolve calcium carbonate, meaning the carbon dissolves in water or is released as carbon dioxide gas,” the researchers wrote in an article for The Conversation. “This huge pool of carbon is affected by changes in the environment, especially soil acidification. Acids dissolve calcium carbonate, meaning the carbon dissolves in water or is released as carbon dioxide gas.”

Inorganic carbon—mostly in the form of solid carbonate minerals like limestone, marble, or chalk—is different from organic carbon like plant litter, bacteria, and animal waste. While the latter has been gaining global attention, inorganic carbon has been largely ignored as a significant tool in the Earth’s process of regulating CO₂ in the atmosphere and a potential source of the climate change-inducing gas.

The study estimates that some 23 billion tonnes of inorganic carbon could be released over the next 30 years, with little knowledge on how this will impact the planet’s land, water, and atmosphere. By comparison, the airline industry emits roughly 1 billion tonnes of CO₂ every year, so this inorganic carbon is a not-so-insignificant amount.

The study’s authors point to the importance of land practices—whether irrigation or fertilization—as well as strategies like improved rock weathering and afforestation can help keep inorganic carbon locked in soils. After all, less CO₂ is the name of the climate change game, and the world’s soil has a big part to play.

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