Don't Sleep on Soil: Huge Carbon Sink is Leaking

Soils contain two thirds of the world's terrestrial carbon reserves – far more than the forests which sit atop the soils – and their accelerating degradation is releasing CO2 into the atmosphere in a process that could spiral out of control.

Scientists call this process desertification, and the soils in Bolivia provide a stark case of this advancing problem: almost half the soil in the nation is being affected.

The final declaration adopted by the recently concluded World People's Conference on Climate Change in Cochabamba called for a reversal of the process of desertification.

The Bolivian Science and Technology Ministry recently announced that "desertification... affects 41 percent of the national territory, 439,432 square kilometers, where 77 percent of the populations lives, some 6.4 million people." Over 89 percent of them are poor, following a well-established pattern in which environmental degradation damages those least able to adapt to it.

Many of the factors that have made the Bolivian soil desertify, such as deforestation, changes in rain patterns, or a general lack of water, are indirectly or directly related to climate change. Desertification occurs as a land-mass dries up, the vegetation on top the soil withers away, the microbes in the soil die, the resulting soil erodes, and its carbon migrates into the atmosphere in the form of CO2.

But desertification is also a feedback loop. Less carbon in the soil, because it has been rendered infertile desert, means more carbon dioxide in the atmosphere. More carbon in the atmosphere means a hotter planet. Plants die, and the soil dries, erodes, and desertifies further. If desertification is a feedback loop, reversing desertification—terraforming, in a way, which is theoretically possible—is also a feedback loop, pulling CO2 from the atmosphere and sequestering it in the soil. Bolivians and the global South are well aware of this, which is why the Cochabamba conference declaration included a clause calling for the "reduction and absorption of the emissions" from the global North.

Despite insistent hype about trees as carbon-banks, the best place to store carbon is not the forests of the world but the land atop which the forests sit, composed of a far larger organic, terrestrial substance, something common and overlooked: soil. Sidelined in discussions of anthropogenic climate change, soil is central to the global carbon cycle and, more generally, to both CO2 drawdown and CO2 emissions.

Indeed, if forestation and de-forestation are important because of how they contribute to emissions and absorption of CO2, how much more important is dirt, which contains so much more of the global terrestrial carbon reserves, in a physical configuration less susceptible to being burned off or chopped down, as trees can be? The Cochabamba conference's 17th working group, on agriculture and food sovereignty, has taken note of this. So has Rattan Lal, the pre-eminent authority on soil science at Ohio State University, John Kimble, formerly with the National Soil Survey Center, and Virginia Tech's Ronald Follett, who commented that soils "play an important role in the global carbon cycle. Thus, important and strategic objectives of selecting soil management options are to decrease the efflux of CO2 from soil to the atmosphere, and increase the total soil organic carbon" store.

Accelerating CO2 release

But such carbon stores are still vulnerable, serving us canaries for all of us. As soil goes, so goes the planet. Soil is also part of perilous feedback loops. The latest research on the topic indicates that as the surface temperature increases, soils seem to sweat increased amounts of carbon into the atmosphere as their carbon stores oxygenate and migrate into the atmosphere as CO2.

As scientists Ben Bond-Lamberty and Allison Thomson observe in Nature, "the available data are, however, consistent with an acceleration of the terrestrial carbon cycle in response to global climate change." In some sorts of soils, the feedback processes will be even more powerful: "the RS [soil respiration] of peatlands—which store an outsized fraction of global soil organic carbon—may increase more rapidly than a temperature-driven model would predict, driven by permafrost melting and increasing peat oxygenation in addition to temperature changes."

As Pete Smith of the University of Aberdeen and Changming Fang of Fudan University add, this analysis "lends strong support to the hypothesis that soil carbon fluxes will increase in a warming climate." As the average global temperature increases, soil in warming regions will pump more CO2 in the atmosphere.

Don't ignore the soil feedbacks

This means that throwing a full brake on global warming is necessary in order to prevent further warming, that feedback loops are already in operation, and that the point is to prevent them from speeding up. This puts discussion of when atmospheric CO2 levels will peak in sharp relief: if they don't peak soon, and warming along with them, humans may lose control of when they peak and the rate of increase—an important consideration of the Cochabamba conference. This makes it clear that although converting soil (and trees) into offsets so that developed nations can keep burning fossil fuels is a deeply flawed idea, using natural methods of drawing down atmospheric CO2 will be necessary, if handled responsibly and thoughtfully.

Indeed, it's worth noting that the Cochabamba roundtables did not discard forests' and soils' ability to absorb CO2. They simply insisted that these measures not detract from reduction in fossil-fuel based CO2 emissions, which are the true disruptors of the carbon cycle and may create an entirely new level of atmospheric CO2. It just happens to be an unlivable level, since it will be hundreds of parts-per-million of CO2 higher than that which prevailed throughout human history. When the soil atop which we stand starts to bleed its carbon into the atmosphere, it will be too late.

See also:

Peak Soil Has a Simple Fix, But Will We Manage It?

Organic Farming Yields Far Better Crop Resistance and Resilience

Can 'Carbon Farming' Limit the Environmental Impact of Beef Production?

Scientists Search for Carbon Solutions in Amazonia's 'Black Earth'


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