Carbon Sequestration:
Agriculture’s Next Revolution
by Wade Collins

By now, hopefully, all of us have come to understand the magnitude of the threat that global climate change poses to the health of our planet. The “warming of the climate system is unequivocal,” states the latest IPCC (Intergovernmental Panel on Climate Change) report issued in February of this year, “as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising average sea level” (IPCC 2007). Temperatures around the world have been documented to have already risen 0.76 degrees Celsius since the beginning of the 19th century, and current atmospheric modeling of global temperatures predicts a further increase of between 1.8 and 4.0 degrees Celsius by the end of the 21st century if emissions of CO2 and other greenhouse gases are not immediately and severely curtailed.

These increases in temperature portend a future that is difficult to comprehend, and chilling in its implications. A six foot rise in sea levels, for instance, would completely inundate countless coastal communities around the world. "The consequences would be catastrophic," says Jonathan Overpeck, director of the Institute for the Study of Planet Earth at the University of Arizona in Tucson in a 2004 National Geographic News article. "Even with a small sea level rise, we're going to destroy whole nations and their cultures that have existed for thousands of years" (Lovgren 2004).

So, global warming is real, is happening right now, and is, unfortunately, going to get much worse. How much worse? This is up to us and we all have a moral imperative to do whatever we can, as a species, as a community, as individuals, to prevent the worst case scenarios from becoming our and our children’s reality.

There are certainly ways each of us can help reduce the impact and severity of global warming. Of course, we can reduce our dependence on fossil fuels, drive less, do a home energy audit, replace energy inefficient appliances and convert to clean energy sources. By doing so we can limit the amount of new carbon dioxide being released as a result of anthropogenic (human created) means. But what, if anything, can be done about the carbon dioxide that is already here with us now, and additionally, that which is going to be emitted tomorrow and on into the foreseeable future? (“Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium, due to the timescales required for removal of this gas from the atmosphere” (IPCC 2007).

As it turns out, one of the best ways to remove CO2 from the atmosphere is to do something which many of you reading this article have already been doing: farming and gardening organically (Hepperly 2003). To be truly effective at removing atmospheric CO2, our agriculture needs to be more than simply organic, it must also be sustainable, and perhaps most importantly of all, it must disturb the soil as little as possible. To understand this better it is important to first take a closer look at the C of CO2.

Carbon is the fourth most abundant chemical element in the universe after hydrogen, helium, and oxygen. It constitutes 18.6% of our body mass, is present in every organic molecule in the human body, and “is the basis of the chemistry of all known life” (Wikipedia).

Carbon is neither created nor destroyed; it is cycled. That is, it moves between a finite number of dynamic storage environments within the Earth’s various ecosystems: the atmosphere, the oceans, the soil, living organisms, and that which is located within fossil fuel reserves. While carbon ebbs and flows amongst and between these “eco-islands,” the process that is most pertinent to the discussions centered around global warming is the one whereby carbon moves into, and out of, the Earth’s soil. Here, plants remove carbon dioxide from the atmosphere, breaking it apart during photosynthesis. The carbon generated as a result of this activity is used for growth and cellular development, while the oxygen, a waste product of plants, is returned to the atmosphere. When a plant dies and decomposes, it releases much of the carbon back to the atmosphere to recombine with oxygen in the form of carbon dioxide. A smaller portion of carbon, primarily that within the root structure of the plant, is stored in the soil in various stages of stability—that stability being dependent upon the activities of soil microorganisms that work to bind carbon within either physically or chemically protective bonds during the production of various humic substances, or SOM (soil organic matter.) This ability of plants to retain carbon in the soil via the production of organic matter that releases less carbon back to the atmosphere than they originally used is called sequestration, and it is one of the key elements for any plan hoping to address global climate change.

Let’s shift our focus to CO2

Carbon dioxide is of critical importance in two very distinct ways. First and foremost, it is the substance that plants “breathe in” to enable photosynthesis. Without it there would be no plants, without plants there would be no oxygen, and without oxygen there would be no us. Although its disappearance would occasion no great outpouring of grief amongst the anaerobic crowd, as it was these frisky critters that ruled the earth before the advent of the oxygenated atmosphere (and to whom oxygen is a deadly toxin) we need carbon dioxide. That is, we need some carbon dioxide. A good round number would be, say, 280 ppm (parts per million), which is what was in the atmosphere at the end of the 19th century. 280 ppm also falls within the natural range of carbon dioxide (180 ppm to 300 ppm) that had existed during the previous 650,000 years. By contrast, in 2005, the atmospheric concentration of carbon dioxide had reached 379 ppm—well outside the established range—and was increasing, at that time, on average, another 1.9 ppm each year.

This brings us to the second point of critical importance regarding carbon dioxide:  too much of a good thing, it turns out, isn’t such a good thing. Carbon dioxide, if it is not sequestered by plant material into the soil, or dissolved into solution within the oceans (it can remain intact for up to 200 years), accumulates. Some accumulation is okay and is necessary for life on earth to exist in its current climate habituations. This is because carbon dioxide, along with several other accumulative gases, traps a portion of the sun’s heat that is reflected off the earth’s surface. Without some accumulation of carbon dioxide the earth’s average temperature would be somewhere in the -18 degrees Celsius range instead of 15 degrees Celsius, which is what it is currently. But too much accumulation traps an excess amount of heat, warming the Earth’s various ecosystems into disruption.

There are two primary ways that carbon dioxide is released into the atmosphere, and therefore two different catch-points available to us to restrict that entry. The first, which accounts for over 70% of global CO2 emissions, results from the burning of fossil fuels.

360 to 280 million years ago, during the Carboniferous Period, vast areas of green organic material were deposited under successive layers of sediment. Over time, that organic residue, consisting largely of carbon, was subjected to enormous amounts of pressure and heat from the continuous and ever-intensifying weight of the earth, and eventually rock, blanketed over it. Through these processes coal, oil, and natural gas were created, forming huge repositories of stable carbon that remained, for all intents and purposes, locked away until their subsequent discovery as fuel and energy sources during the Industrial Revolution of the late 19th century. Burning these various fossil fuels over the last century and a half has released this formerly bound carbon, as carbon dioxide, into the atmosphere, transforming this ancient relic of the Paleozoic past into a monumental modern-day catastrophe.

Prior to the Industrial Revolution carbon dioxide was still being released into the atmosphere as part of the normal carbon cycle resulting from the decay of organic material, and also from volcanic activities. But there was another human-initiated technological revolution responsible for the bulk of carbon dioxide emissions not accounted for by future fossil fuel use, this one agricultural in nature.

The development of agriculture some 10,000 years ago initiated a series of land use practices that, while commonplace and widespread today, caused a significant shift in the equilibrium of the carbon cycle: specifically the clearing and burning of forests to accommodate an increased demand for areas under cultivation, and the exposure of subsurface organic matter to atmospheric conditions and erosion through increasing use of the plow. As the FAO (Food and Agriculture Organization of the United Nations) report entitled Carbon Sequestration in Dryland Soils points out, “the mold-board plow and disc harrow are believed to be the causes of the loss of soil C (carbon) through the destruction of soil aggregates and the acceleration of decomposition by the mixing of plant residues, oxygen, and microbial biomass” (FAO 2004). These activities allow for the release of carbon that would have otherwise remained in the various sequestration loops within the soil. That carbon, once allowed to re-enter the atmosphere, is free again to combine with oxygen to form carbon dioxide. To this day, agriculture remains a significant source of greenhouse gas emissions—roughly 30%—and certainly much more, if transportation and storage issues are factored into the equation.

Turning this around—that is, transforming agriculture into a process that has a positive, rather than negative, impact on global climate change—forms the basis for a truly sustainable practice of land and crop management that benefits all of us. This goal of an agriculture which is responsive to the amelioration of global climate change recognizes the various points at which agricultural practices intersect with the global carbon cycle, and employs them in such a way that inputs of carbon are increased (soil sequestration) while outputs (emissions) are reduced. Organic agriculture already has many elements in place that make it suitable for achieving these ends. Because pesticide and chemical fertilizers are not utilized, for instance, fossil fuel use is reduced both in the means necessary to produce such products in the first place and in the elimination of emissions produced when applying them. If we restrict our practices to only organic methods we lose many, if not most, of the opportunities for enhanced sequestration and further reductions in CO2 emissions that can also be realized through incorporating reduced tillage practices. Key elements of a new sustainable agriculture must accentuate positive methods of intervention that strengthen processes that already exist in nature. If tilling our gardens and farms is a net producer of CO2, we must create viable no-till options for maintaining and increasing organic matter in these spaces. By doing so, not only do we decrease emissions, but we also increase the capacity of the soil to store increasing amounts of carbon. Taking advantage of the propensity for plant roots to sequester carbon at higher rates, emphasis should be given to crops or intercrops with deep root structures (planting strips and beds of perennial prairie grasses or clover between permanent areas of no-till annual crop production). Green manuring, or cover cropping between cycles of crop production, especially with plants capable of fixing nitrogen, also creates a beneficial ratio of carbon input compared to output.

Carbon, carbon dioxide, and agriculture: these three elements form a nexus of opportunity for addressing global climate change. Growing organically, making the shift to no-till practices, using intercrops of deep-rooted perennials, and incorporating green manures into one’s planting schedule are among the tools available to us as we move forward to a new alignment between food production and the environment. Can we “grow” enough carbon on our farms and in our gardens to make a difference? Although “the use of carbon sequestration options should not distract us from the goal of reducing dependence on fossil fuels, the cause of the problem in the first place (FAO 2004),” they have the potential to extract enough carbon dioxide from the atmosphere to forestall many of the worst aspects of future warming scenarios. By transforming our agricultural practices to prioritize the accumulation of carbon in our soils, we can all play a role in this effort, bringing us a future where we all might be able to breath a little easier.

Wade Collins
Seeds of Change Research Farm Associate

IPCC. 2007. Climate Change 2007: The Physical Science Basis; Summary for Policymakers. 5, 17. http://www.ipcc.ch/SPM2feb07.pdf.

Lovgren, Stefan. 2004. Warming to Cause Catastrophic Rise in Sea Level? National Geographic News http://news.nationalgeographic.com/news/2004/04/
0420_040420_earthday.html (accessed November 15, 2007).

Hepperly, Paul. 2003. Organic Farming Sequesters Atmospheric Carbon and Nutrients in Soils. The Rodale Institute. http://www.strauscom.com/rodale/rodale-whitepaper.html (accessed November 15, 2007).

Wikipedia. http://en.wikipedia.org/wiki/Carbon.

Food and Agriculture Organization. 2004. Carbon sequestration in dryland soils. Chapter 4.  http://www.fao.org/docrep/007/y5738e/y5738e00.htm (accessed November 15, 2007).

Photo Captions: (1) Joe Martinez direct seeds into an untilled field. This practice helps increase carbon sequestration in soils.