Sunday, November 01, 2015


Soil as Carbon Sink

My last post acknowledged the dramatic shift in Gaia's order caused by the advent of the Anthropocene, the newly-named geological period in which Homo sapiens has become what Brian Swimme calls a “planetary power.” I began this series of posts by examining some of the proposals for geo-engineering in the face of momentous climate change, particularly emphasizing the advantages of limiting incoming solar radiation, versus the much costlier methods of carbon capture and storage (CCS).

I received responses from two people I highly respect, each of them questioning my analysis. The first pointed out that I had overlooked the potential of carbon sequestration in soils, something I was aware of, but indeed overlooked in my emphasis on the high-tech quality of anthropocentric mediation of a typically anthropocene problem. The gentleman linked me with the Rodale Institute's study, “Regenerative Organic Agriculture and Climate Change”, which I had seen but not read.

I will return to that study, but lay out the topic with the aid of a characteristically comprehensive review of the subject by Judith Schwartz, “Soil as Carbon Storehouse: New Weapon in Climate Fight?”, in Yale's Environment 360. Schwartz summarizes many key studies, stating at the outset that 50-70% of the world's original soil carbon stock has been lost, almost all oxidized as CO2. The essential job is to restore this carbon by recovering degraded lands, primarily long-grass prairies, but also wetlands and of course forests. The most promising sites for restoration include the former NA prairie, the North China Plain, and the parched interior of Australia. This would be a triple-win, sequestering CO2, boosting soil productivity (restoring dirt to actual soil), and increasing resilience to floods and drought.

The methods by which this could be achieved include cover cropping, no-till or minimal till (strip-till) agriculture, and agro-forestry, where croplands, trees, and ruminant animals would be integrated into one interrelated system. Some of the key principles wold be mulching rather than burning, largescale use of biochar, and restoration of mangroves, salt marshes, and sea grasses.

Schwartz quotes liberally from an interview with biogeochemist Thomas Goreau, who makes the key point that current efforts to slow the climate change train are focused on CO2 sources, whereas we need to look equally at its destination – where CO2 can and should go. Goreau says that degraded, deforested land could create biochar for housing soil carbon by using the on-site weeds for pyrolysis.

An important vehicle for moving carbon into soil is root - mycorrhizal – fungi. Discovered only in 1996, recent research shows that these fruiting, mushroom-like bodies can enable soils they inhabit to absorb 70% more carbon per unit of nitrogen. This confirms the theory of Rudolf Steiner, father of biodynamic gardening, a century ago. Now what seemed quasi-mystical has a firm “scientific” basis. That is, Goethean/Anthroposophic science now has confirmation from the more reductive type.

Schwartz has recently published a book, Cows Save the Planet and Other Improbable Ways of Restoring Soil to Heal the Earth, in which she argues for Holistic Planned Grazing, pioneered in Argentina and Zimbabwe, where livestock grazing is patterned after wild ruminants' co-evolved grazing pattern with traditional grasslands. Animals are moved to prevent overgrazing, and in the process not only is their manure evenly spread, but their trampling aerates the soil, pushing seeds in as well as dead plant matter, so that soil micro-organisms can get to work. Add this method to restoring grasslands by replanting long-rooted indigenous varieties, and you have a recipe for vigorous carbon sequestration in the 20% of the land that is grassland. 
So how much excess carbon can the soils store? The Rodale study extrapolates from plots in four parts of the world to claim from 50% to over 100% of current emissions. Rattan Lal at Ohio State puts the figure at 10-33%. However, researchers in prairie grasses say that this could be increased if one were to extensively replant perennial grasses with root systems from 1 to 5 meters, rather than conventional carbon measurements that go only 15-30 cmm. At the conservative end of the scale, senior scientists Rolf Sommer and Deborah Bossio at the International Centre for Tropical Agriculture conclude that soil carbon sequestration has a limited potential when one takes into account the variety of possible sites. At best, they say, we can expect 9% of current emissions the first few decades, with less ability to absorb CO2 over time. But as Bossio says, “Every bit helps.”

More research needs to be done – the field is still new – but clearly the Rodale Institute study is hyped. One of their test plots, in Thailand, is done on an “unreported crop” - hardly a scientifically specified finding. Extrapolating data from this plot, they get 32 gigatons of of CO2/year of sequestered carbon, precisely the amount currently emitted. How convenient.

On a planetary scale, the ocean stores by far the most CO2, and it has absorbed about as much as it can, resulting in ocean acidification that threatens many lime-based species, and the marine foodchain itself. This happens without our engineering anything. With a return to more traditional organic farming, including a hugely increased role for biochar, extensive use of HPG grazing techniques, and an all-out effort to restore perennial prairie grasses, a significant portion of current CO2 emissions could be stored in soils, relieving the beleaguered ocean. And all of this would help feed our growing population in a way that works to regenerate degraded soils.

Along these lines, Wes Jackson at the Land Institute in Salinas, Kansas has patiently led a team of researchers who are back-crossing perennial prairie grasses to produce seed kernels big enough to harvest. I heard him in conversation with Wendell Berry at a food and spirituality conference at Duke a few years back, and he was an inspiration.

The advance agenda for the COP 21 gathering in Paris does not indicate that soil carbon storage is being highlighted as a significant strategy to sequester CO2. The focus is on reducing emissions (mitigation) and paying the costs of adaptation for the poor countries already hit by climate change. Hopefully it will emerge from the dark ecological underground as a robust competitor to the technocratic agenda, amplifying the highly compromised REDD forest carbon market mechanism. We all await - with a mixture of eagerness and dread - the results of this key moment in planetary history.

But whatever happens in Paris to move the “demand side” onto the table (i.e CO2's destination, rather than its sources, or “supply”),with agroforestry and silviculture taking the place of unaffordable CCS, world powers will not sit idly by if sequestration lags behind the worrisome rise in levels of emissions. Current national plans to limit emissions put the world on a trajectory to 3 degrees C of warming, which is double the maximum safe level, and would assure a runaway climate system, unless we can find a sink beyond the maxed-out oceans for the relentless stream of CO2. Soil carbon sinks can be optimized, but the research does not make me confident that this will be sufficient to the task.

So I submit that methods to reduce incoming solar radiation are going to remain on the table, hopefully with increasing levels of public discussion, so that all parties are clearly represented, and sober decisions made. At least nobody is still seriously interested (i.e. with their checkbooks ready) in the pipedream of CCS that was long encouraged by fossil fuel companies, so we wouldn't be so concerned about current emissions. You know, just pump it under the ground, or to the bottom of the oceans, and we can forget about it.

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