Soil as a solution

Metres deep and in every direction, soil is everywhere. Most people don't even think about it, but soil could be the next solution to climate change.

Soil stores a massive amount of carbon, with about 3000 gigatonnes of carbon in the top 2 metres of soil. Soil carbon debt of 12,000 years of human land use — research article But in the last 200 years, modern farming has lost about 133 gigatonnes of this carbon back into the atmosphere.

The theory is, if there used to be that much carbon in the ground, why can't we just recapture it and put it back where it belongs? The idea has made a lot of people very interested, not least farmers, whose crops depend on the soil.

Carbon farming

In fact, with just a few changes to how farms are managed, many people believe significant amounts of carbon could be removed from the atmosphere. This kind of farm management is known as regenerative agriculture or carbon farming.

There's a few main methods. Crops can be planted to cover exposed soil, e.g., between rows of crops, or to protect unplanted fields during winter. Fields can be tilled without disturbing the soil. Grazing animals can be quickly rotated between fields to ensure they don't expose or damage the soil. Compost works too, to cover the soil, and shift carbon underground. How carbon farming can help solve climate change — The Conversation

The idea has attracted political backing. The French government launched an international campaign in 2015 called "4 Per 1000". In English it means "4 parts per thousand", or 0.4%. The idea is that, if levels of carbon in the soil can increase by 0.4% each year, it could be enough to stall climate change and give us enough time to find a better solution. The 4p1000 initiative

Carbon farming even has financial support. The Terraton Initiative believes that a 0.5% increase in soil carbon levels could remove 1000 gigatons, or a terraton, of CO2 from the atmosphere, and is willing to fund farmers who help to reach that goal. Can farmers and ranchers pull one trillion tons of carbon dioxide out of the atmosphere? — Terraton Initiative

The targets seem possible. In one study over 20 years, farmers managed to raise soil carbon content by 12.6 percent, or about 0.7 percent annually, using just compost and cover crops. Compost key to sequestering carbon in the soil — research article

Biochar

But why limit ourselves to a 0.7% increase in soil carbon? Biochar can increase the carbon in the soil by about 40%, according to an analysis of over 400 studies of biochar. Responses of soil carbon sequestration to climate smart agriculture practices: A meta‐analysis — research article

Biochar is wood heated at several hundred degrees and burned without oxygen. What's left is a charcoal-like substance with a high concentration of carbon, called biochar.

Farmers use biochar to improve soil quality, but it also works to trap carbon underground for thousands of years. Biochar — Wikipedia

Biochar — a 39% increase in soil carbon. Oregon Department of Forestry, CC BY-NC 2.0

Biochar is so effective in trapping carbon that one study estimated a reduction in CO2 emissions of 130 gigatons over a century. Sustainable biochar to mitigate global climate change — research article

Fungii

Then there's fungii. Invisible to the eye and deep in the soil, they're easily overlooked. But there are literally tons of fungii in a single hectare of land, and some are very good at storing carbon. So good that some kinds of fungii could lead to 70 percent more carbon stored in the soil. Symbiotic fungi inhabiting plant roots have major impact on atmospheric carbon, scientists say — Science Daily

Fungii's carbon-trapping capabilities inspired Australian Guy Webb to look for ways to maximise the potential of fungii. After much research and a couple of companies — SoilCQuest SoilCQuest and Soil Carbon Co., Soil Carbon Co. he believes he has a solution that could store 8.5 gigatonnes of carbon each year, if used on all farmland globally. This translates roughly to the same as the amount of CO2 emitted each year. Coating seeds in these microbes superpowers plants’ carbon capture abilities — FastCompany

Mycelium - a fungus that connects the root systems of trees and stores carbon. Grzegorz Jaglarski, CC BY-SA 3.0

The solution seems easy. His idea is to produce seeds coated in a microbe known for its carbon-storing properties — melanised endophytic fungi. As CEO Guy Hudson explains, with farming, "we don’t need to build additional infrastructure. We don’t need to train a new workforce. It’s all there already." All farmers need to do is to use seeds coated in the microbe. Coating seeds in these microbes superpowers plants’ carbon capture abilities — FastCompany

Global soil warming

Carbon farming looks like it could to make a difference, to agriculture, the soil, and to climate change.

There's just one major obstacle — something called global soil warming.

The problem is that, as the temperature of soil rises, it releases CO2. Unfortunately it's a vicious cycle, which scientists call a positive feedback loop. CO2 raises temperatures which heats up the soil. Warmer soil releases more CO2, and soil temperatures increase some more, and so on. Carbon released by warming soils could trigger a disastrous feedback loop — ScienceAlert

One study suggests that even with just 1 °C (1.8 °F) of global warming, somewhere between 30 and 203 gigatonnes of soil carbon could be lost. Quantifying global soil carbon losses in response to warming — research article Unfortunately the planet is predicted to warm by much more than just a degree, more than 3 °C (5.4 °F) degrees of warming possible by the end of this century. The CAT thermometer

It's a race between carbon farming and global soil warming to keep CO2 trapped in the ground. We need to win.