Por Mauro Rebelo

Fix the soil and Carbon, and many other things, will fix themselves

global carbon stocks
Global Carbon Storage compartments. Taken from https://www.fs.usda.gov/ccrc/topics/global-carbon

Most claims on climate change are based on the verifiable increase in CO2 in the atmosphere. This increase has been substantial compared to what Earth has experienced over the last millenia. It is hard to anticipate which changes this increase can cause, so it is a good strategy to try to mitigate it and prevent further.

The CO2 that went into the atmosphere was stored somewhere else. The image that illustrates this post depicts the compartments and the amount of CO2 in each. Most is in the ocean. But the second largest compartment is vegetation and the soil. For most purposes, Earth is considered a closed system. Besides one meteor or another coming in, one rocket or another going out, the number of atoms on earth is stable (curiosity fact: Earth and Mars apparently exchange about 10g of dust a year).

I have to say that the first time I saw this data I was a bit surprised. I knew that Oceans, because of the bicarbonate buffer system, had A LOT of carbon. It is intuitive to think of forests as another huge compartment. But soil?! Unless you know what soil is really about. I like this explanation at the beginning of MIT’s climate portal:

“Soils are made in part of broken-down plant matter. This means they contain a lot of carbon that those plants took in from the atmosphere while they were alive. Especially in colder climates where decomposition is slow, soils can store – or “sequester” – this carbon for a very long time.”

Like most atoms that are nutrients, Carbon has a cycle, moving from one compartment to another driven by biotic (biological) and abiotic (physical, chemical and physico-chemical) forces. The global carbon cycle is depicted here:

Carbon cycle.jpg
Diagram adapted from U.S. DOE, Biological and Environmental Research Information System. – http://earthobservatory.nasa.gov/Features/CarbonCycle/ Taken from: https://en.wikipedia.org/wiki/Carbon_cycle

While industrial and fossil fuels burning emissions are responsible for most of the CO2 going to the atmosphere, land use change is second to it.

“[…] converting natural ecosystems like forests and grasslands to farmland disturbs soil structure, releasing much of that stored carbon and contributing to climate change. Over the past 12,000 years, the growth of farmland has released about 110 billion metric tons of carbon from the top layer of soil2-roughly equivalent to 80 years’ worth of present-day U.S. emissions” says again the MIT page.

Recovering soil is a key strategy to reduce CO2 remobilization to the atmosphere. FAO’s Global Soil Partnership has a country-driven global estimation of SOC sequestration potential around the world(GSOCseq) and a compendium of good practices for farmers“Recarbonizing global soils” on how to maintain SOC stocks and how to sequester CO2.

“Replenishing and protecting the world’s soil carbon stores could help to offset up to 5.5bn tonnes of greenhouse gases every year.”

says Dr. Deborah Bossio, lead soil scientist at the Nature Conservancy, in an article published in Nature Sustainability.

Recovering soil is also a very transversal measure that touches several important aspects of environmental quality and sustainability: carbon cycle, pollution control (preventing nutrient run-off and river eutrophication), water quality, microbial biodiversity, food safety… All of which are UN’s Sustainable Development Goals – SDG.

But recovering degraded soil is not an easy task at all!

There are hundreds of millions of farmers around the world, mostly farming small plots of land. To take full advantage of soil-based sequestration as a climate solution, we would need many of them to change the way they farm, now and for hundreds of years in the future. This is a big social and economic challenge, and experts debate how much soil-based sequestration is really possible over the long term.

States the MIT page while Dr. Bossio says:

“There’s a lot of barriers right now to change in our agricultural systems. One of the biggest is disincentives in agricultural policy. There’s also a lack of knowledge about changing current practice. We tell farmers ‘just plant cover crops’ – but that means a farmer needs to know when to plant them, which to plant and how to manage them.”

So it is reasonable to understand the skepticism of some scientists that this trend will be reversed on a global scale. But one way to do that would be to create products that help farmers change their practices. Biotechnology can lend a hand.

An article on Forbes talks about a new generation of biotech firms that claim they can turn the world’s soil into a vast carbon sink, absorbing up to a quarter of annual emissions. One such company is Soil Carbon Co., based in Australia. They are tailoring communities of microbes that live within farm soil to turn back the clock on human emissions while producing better crops. Their CEO Guy Hudson explains:

“We develop microbiological seed treatments comprised of microbial fungi and bacteria designed to provide plant benefits. As that plant grows it exudes sugars into the soil that are converted into stable soil carbon by the fungi.”

Hudson says this solution enables the soil to quickly build significant quantities of stable carbon, stored in tiny balls of soil called microaggregates, preventing the carbon from being released back to the atmosphere.