Trillions of Tons of Carbon Are Missing from Climate Models

Draft script:

From Popular Mechanics comes this headline on 22 April 2024: Trillions of Tons of Carbon Are Missing from Climate Models. The story begins with three bullet points: (1) 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; (2) A new study focuses on the role of soils as both a storage for and emitter of carbon, and found that 23 billion [metric] tonnes of inorganic carbon could escape soil over the next 30 years; and (3) Good land management—as well as other practices, such as afforestation and improved rock weathering—can help slow down this significant source of CO₂.

Here's the lede: “The sole purpose of people and programs combating climate change is finding ways to keep carbon out of the atmosphere.” The first paragraph continues: “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.” A minor detail is worthy of mention: Planting trees is not necessarily a big help, as I pointed out previously in this space.

The article goes on: “the top two meters of soil beneath our feet currently hold roughly 2.3 trillion [metric] tonnes of inorganic carbon—five times more than all of the terrestrial plants on Earth combined.” The article in Popular Mechanics refers to a paper in the prestigious, peer-review journal, Science, in the next paragraph: “… the top two meters of soil beneath our feet currently hold roughly 2.3 trillion [metric] tonnes of inorganic carbon—five times more than all of the terrestrial plants on Earth combined.

Information from the paper in Science continues in the next paragraph: “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—it’s 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.”

The bottom line from the article in Popular Mechanics is “… less CO₂ is the name of the climate change game, and the world’s soil has a big part to play.”

In addition to the reference to Science, the article in Popular Mechanics also refers to an article in The Conversation written by some of the authors of the peer-reviewed paper in Science. The piece in The Conversation was published 12 April 2024 and titled Trillions of [metric] tonnes of carbon locked in soil has been left out of environmental models – and it’s on the move. The article in The Conversation explains carbon in the soil: “… if we do think about carbon in soil, we are usually thinking of carbon in organic matter in the soil, such as plant litter, bacteria or animal waste. However, the inorganic, mineral component of soil also contains carbon.

In a new study just published in Science, we show there is much more soil inorganic carbon than anybody realized – and that it may be a surprisingly big player in Earth’s carbon cycle.

We analysed more than 200,000 soil measurements from around the world to calculate that the top two metres of soil globally holds about 2.3 trillion [metric] tonnes of inorganic carbon. This is about five times more carbon than found in all the world’s terrestrial vegetation. We estimate some 23 billion [metric] tonnes (1%) of this carbon may be released over the next 30 years, with poorly understood effects on Earth’s lands, waters and atmosphere.” The 23 billion tonnes of carbon is 1% of the 2.3 trillion tonnes of inorganic carbon contained in the top two meters of soil in the world. In other words, the release of only 1% of this enormous amount of inorganic carbon contained within the top two meters of soil in the world is subject to release into the atmosphere, “with poorly understood effects on Earth’s lands, waters and atmosphere.”

The paper in Science was authored by 27 scholars. Titled Size, distribution, and vulnerability of the global soil inorganic carbon, it was published on 11 April 2024. The Editor’s summary includes this information: “Soil inorganic carbon has taken a back seat to its cousin, organic carbon, in most analyses investigating the role of soil in the global carbon cycle. Huang et al. [This paper] addressed that imbalance by analyzing a large database of field-based soil inorganic carbon measurements … to estimate better how much inorganic carbon exists in soils globally and how vulnerable it is to future loss. They found that [N]early one billion tons of inorganic carbon are lost to inland waters annually, and that future losses will reduce global SIC soil inorganic carbon by 23 billion tons over the next 30 years under a business-as-usual scenario. This value represents a substantial component of atmosphere and hydrosphere carbon dynamics.” Obviously, the 30-year figure is almost certainly irrelevant, based on peer-reviewed papers I have discussed previously.

The take-home message from the paper in Science is summarized in the final sentence of the Abstract: “Our synthesis of present-day land-water carbon inventories and inland-water carbonate chemistry reveals that at least 1.13 [+ 0.33] billion [metric] tonnes of inorganic carbon is lost to inland-waters through soils annually, resulting in large but overlooked impacts on atmospheric and hydrospheric carbon dynamics.”

This is a tremendous amount of overlooked carbon. As with most of the information I present in this space, the consequences are undesirable. Nonetheless, I prefer to know the facts rooted in evidence. If you’re still watching, then you do, too.