Soil carbon types & carbon flows

Recognizing the soil carbon sponge to counter global warming

By Peter Donovan
In a series of talks in California in April 2018, I was privileged to hear Walter Jehne, founder of Healthy Soils Australia, help us recognize the soil carbon sponge for what it is or can be. The soil carbon sponge is porous, well-aggregated soil rich in plant roots, diverse life forms, nutrient availability, air, and often holding lots of water.

Though this description is short and simple, it conceals a circular, barely visible complexity. The soil carbon sponge is both cause and effect of the kind of water and carbon cycling that supports basic human needs such as quality and quantity of human food and fiber, breathable air, drinkable water, biodiversity, and climate regulation.

Weather extremes, soil degradation, and climate change have focused broad attention on soil, on carbon, and on water cycling. But the complexity and circularity is challenging. The most powerful planetary force–coupled carbon and water cycling, the circle of life, the soil carbon sponge–remains camouflaged behind a mixture of disconnected facts, problems, and assumptions.

As Walter observed, the elephant is not even in the room. Here’s why:
1. Reactive orientation. Our human default is to react against what we fear or don’t want. We are quick with blame, labels, and judgment of good or bad. We simplify our world to linear cause and effect.
2. Vested interests. Many of our large economic sectors, both public and private, treat the symptoms of degraded soil: fertilizers, herbicides, pesticides, irrigation, crop insurance, flood control, repairing infrastructure after erosion and sedimentation, waterworks and water treatment, fire suppression, management of human disease and malnutrition, disaster mitigation and recovery, wildlife conservation, and even advocacy on climate and environmental issues entrenched in opposition to other vested interests.
3. Specialized knowledge. Experts often have a vested interest and power in defending what they know, and supplying solutions, predictions, and answers. Experts become gatekeepers, guarding the problem definitions that match their expertise while lacking contexts and effectiveness for complex or wicked problems.

These habits and loyalties reinforce each other. We reward the railroading of a problem (or symptom) into best management practices, spend enormous time and treasure, and often worsen the situation. We manage against what we don’t want. We manage and struggle over the parts–agricultural inputs, the Farm Bill–and hope that the wholes will come right.

Walter Jehne, who is a climate scientist as well as soil microbiologist, described several aspects of water cycling that are both cause and effect of the soil carbon sponge. As Allan Savory has long emphasized, the condition of the soil surface, and what’s growing on it, controls the fate of rainfall.

Figure 1: How the Soil Carbon Sponge compares with degrading farming practices.

Deforestation, fire, and agriculture have tended to move landscapes leftward in figure 1, baring soil, increasing fine dust particles that nucleate haze but not rain, planting short-season annuals, shortening the length of green season and the sugary plant root exudates that feed soil porosity and aggregation. Bare soil heats up, radiates, and some of this heat is re-radiated back from greenhouse gases. Regular fire or tillage bares soil and prevents the soil carbon sponge from developing. High-pressure domes over large expanses of hot bare ground repel rain. These landscapes multiply heat and aridity.

On the right in figure 1, the formation of high-albedo rain clouds from abundant transpiration with bacterial precipitation nuclei helps recycle water locally, while the pressure drop from large-scale condensation drives the biotic pump, which brings in moist air from the oceans. When the clouds clear, heat can escape. Abundant plants harvest atmospheric moisture as dew. More solar energy is dissipated upwards by transpiration, and less by sensible heat. These landscapes multiply rainfall and cooling.

The soil carbon sponge may increase your local multiplier for rainfall–the number of times that water is recycled from soil to sky and back again before it leaves your area, either as vapour or runoff. If you are in a dry area, increasing your multiplier can be significant!

To shift a landscape to the right in figure 1, keep in mind the soil health principles: integrate livestock, cover the soil, diversity, living roots as long as possible, minimize tillage. There is some evidence that a reduction in summer fallow (from 77 million to 20 million acres in the northern plains of the U.S.), and an increase in summer plant cover may decrease temperatures and allow for more convective precipitation (see Gerken et al. below).

The vast majority of the heat balance in our blue planet, Walter noted, is governed by water. Australian Peter Andrews wrote, “Plants manage water, and in managing water, they manage heat.”

The opportunity to cool our planet, Walter emphasized, is by influencing the hydrological cooling processes, for which plants and the soil carbon sponge are critical. He suggested that a small increase in high-albedo convective cloudiness might even be enough, and if the soil carbon sponge could be increased rapidly, cooling could be correspondingly rapid.

Increasing soil carbon not the answer to rising temperature

By contrast, for many decades the focus of climate action and policy has been on limiting or reducing atmospheric carbon (carbon dioxide, methane) by reducing emissions, or some kind of “drawdown” such as increasing soil carbon. These strategies, widely implemented, would be undoubtedly beneficial. There is abundant supporting evidence that atmospheric carbon dioxide and methane have and will continue to warm our planet.

However, we have passed the point at which these proposed strategies are likely to yield safety in any kind of near term. The oceans have absorbed so much carbon that, in a drawdown scenario, they will equilibrate with or outgas to the atmosphere in accordance with Henry’s Law (see further reading section below).

Walter Jehne writes: “After over 50 years of warnings and 30 years of global policy denial and delay, it is now too late for reductions in future CO2 emissions to adequately slow down its rise or its greenhouse effects. It is now too late even for the drawdown of carbon to zero or negative net emissions, by itself, to prevent accelerating the dangerous hydrological feedbacks and climate extremes.”

How do we understand carbon, and its relation to climate change? Here are two different views. They do not contradict each other, and it’s not about right or wrong here, but these two embody different possibilities or outcomes:
A. Carbon is a greenhouse gas in the atmosphere (carbon dioxide and methane), and its increase is the principal cause of climate change. There are sources and sinks of atmospheric carbon. To slow, stop, or even reverse climate change, we need to manage against atmospheric carbon by limiting emissions, by drawdown or sequestration into sinks, or both. We can approximate the predicted effects on surface temperatures, sea level rise, and regional rainfall with models.
B. Carbon embodies the solar-powered circle of life, the great biogeochemical carbon cycle powered by photosynthesis and governed by the metabolisms and choices of zillions of self-motivated living organisms, most of them microbes. Though the work of carbon cycling is tiny compared to the work of water cycling, carbon cycling wields enormous leverage with its complex and transformational chemistry, leading to a coupled carbon and water cycling that governs the balance between incoming solar radiation and outgoing longwave radiation. In the soil, the decomposition of living things forms the soil carbon sponge, which can resiliently sustain plant life, affect the earth’s hydrology and heat balance, and may give humans the near-term leverage we need to avert catastrophic climate change, restore hydrologic function, maintain our economies and civilizations, and maintain and enhance human health.

The fixation of much climate policy and activism has been on carbon as a greenhouse gas, that we can and should manage against. In part this is a “streetlight effect,” where it’s easier to look for a dropped object where there is light to see by, rather than in the dark where we dropped it.

Atmospheric carbon dioxide is measurable and its effects could be modeled, and by 1980 it was fairly clear to some scientists that humans were responsible. Water cycling and hydrologic factors were known to be responsible for most of earth’s heat dynamics, but they were not so easily observed or modeled, and perhaps too vast for humans to have influenced. In the models, atmospheric water became a secondary feedback to carbon dioxide, and flooding, drought, and dehydration of landmasses became effects of CO2 rise rather than the circular cause/effect complexes of the circle of life.

The results of this fixation–understandable, evidence-based, and well-intentioned as it is–have been serious:
1. Substitution of simple, more linear models of carbon and water cycling for real-world complexity and mystery
2. Lack of progress in reducing emissions or detectable “drawdown,” in spite of billions of dollars and person-hours spent
3. Climate issue becomes inactionable with enduring conflict, skepticism, fragmentation, and declining hope and trust. Separation of agency from intention, divorce between what we know and what we do.

The real opportunity is B, the circle of life, manage for solar energy flow into plants and the soil carbon sponge, more photosynthesis and slower respiration/oxidation. There’s tremendous complexity in this, and feedback is required to learn it, both as individuals and society. We need more streetlights! (e.g. atlasbiowork) We believe that carbon provides us with an opportunity to restore living biosystems. It is an essential piece of a larger functional whole.

Our focus can shift from carbon as a problem to carbon as an opportunity by asking better questions about how that carbon is functioning. For example, instead of asking how we might affect atmospheric CO2, we might ask, how can I connect these 3 things: my intention, my agency or influence, and the most powerful planetary force (circle of life).

Walter noted that nature has been doing all of this since plants and fungi colonized the bare rock of land masses hundreds of millions of years ago. “We can lift our boot off nature’s throat.”

Source: Soil Carbon Coalition USA May 2018

Q & A
Q. Do you mean to suggest that high and increasing atmospheric carbon dioxide is not a problem, not a risk?
A. Atmospheric CO2 is not a direct risk–we can survive and even thrive in much higher concentration than 405 ppm–but it constitutes a huge risk because of the effects of its climate forcing: dangerously high temperatures, rising sea levels, superstorms, increasing flood and drought, and all the human consequences of those. However, as described above, because of the immense amount of carbon absorbed by the ocean, and our seemingly limited ability to reduce global emissions or get sufficiently large-scale “drawdowns” underway, we probably won’t be able to fix the CO2 issue in any kind of near term.
Q. Do you mean to suggest that soil carbon sequestration is beside the point?
A. Again it depends on how we frame things, what questions we ask. With the usual kinds of greenhouse gas accounting, increasing soil carbon is probably beside the point. As growing the soil carbon sponge, it’s extremely important for all kinds of reasons.
Photosynthesis, which drives carbon cycling, only captures about a quarter watt of sunlight energy per square meter of the earth’s surface, on average. Water cycling captures about 80 watts per square meter (global average over all seasons, night and day, all latitudes), and thus does about 320 times the work. We need to ally ourselves with the big one.
It is in these water dynamics where the dangerous effects of climate change are, and this is where the remedy may lie, as Walter Jehne has been emphasizing for the last dozen years or so. The transformational chemistry of living organisms creates the carbon-glued soil aggregate, the soil carbon sponge, that is our fundamental hydrological infrastructure, and on which our other infrastructures of asphalt, steel, concrete, technology, economy, and civilization depend. (see also

Further reading
Regenerate Earth by Walter Jehne
“The biology of global warming and its profitable mitigation” a 2006 paper by Walter Jehne
Gerken et al.:
(abstract, article behind paywall)
see also (abstract, article behind paywall)
Habits influence perception: 2-minute rotating mask “illusion” It can be difficult to “see” the concave side of the mask as we’re so accustomed to a convex human face. It can likewise be difficult to maintain a focus on managing FOR what we need if our habits, vested interests, accumulated knowledge and experience, and surrounding cues make it easier to align ourselves AGAINST what we don’t want. See also
Ocean buffering of carbon dioxide drawdown
Henry’s Law states that the partial pressure of a gas above a liquid equilibrates with the dissolved concentration of the gas in the liquid. This explains ocean acidification, but a less recognized phenomenon is its reversal, if significant drawdown of atmospheric carbon dioxide were to occur.
An example: carbonated beverages contain dissolved carbon dioxide (carbonic acid). Before opening, the gas above the liquid in its container is almost pure carbon dioxide, at a pressure higher than atmospheric pressure. The pressure declines with a hiss when you open it, the gas escapes, lowering the partial pressure (and concentration in ppm) of carbon dioxide above the liquid. With the cap left off, the dissolved carbon dioxide comes out of solution, and the beverage goes flat.
Hansen, James, Makiko Sato, et al.: Young people’s burden: requirement of negative CO2
Long Cao and Ken Caldeira: Atmospheric CO2 stabilization and ocean acidification

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