Can farmers and ranchers pull one trillion tons of carbon dioxide out of the atmosphere?

By David Perry and Geoffrey von Maltzahn

The short answer is yes, they can.

First, a little background: atmospheric concentrations of carbon dioxide have been rising significantly since the beginning of the Industrial Revolution. In May, the Mauna Loa Observatory in Hawaii reported an average monthly level of carbon dioxide above 415 ppm, the highest concentration of atmospheric carbon dioxide in millions of years (I,II). This accumulation represents an additional 135 ppm of carbon dioxide in the atmosphere since the Industrial Revolution, which equates to one trillion tons* of carbon dioxide, or one teraton (III). **

To avoid the harshest effects of these additional greenhouse gases in the atmosphere, we must reduce current emissions – but even that will not be enough. Even if all countries meet their commitments under the Paris Agreement, and all companies meet their individual commitments, atmospheric carbon dioxide levels will continue to climb, reaching an estimated 580 ppm by the end of the century (IV). This uncertain future cannot be averted with a business-as-usual mindset, nor a middle of the road effort. Drawing down atmospheric carbon dioxide is necessary to begin undoing the damage.

Math behind The Terraton Initiative

Soil represents the third largest pool of carbon on the planet, after the ocean and fossil fuels (V), holding approximately 1.5 trillion tons of soil organic carbon down to a depth of a meter, equivalent to 5.5 trillion tons of carbon dioxide (VI, VII).*** This pool of soil organic carbon is 5.5 times larger than the additional teraton of carbon dioxide that has accumulated in the atmosphere over the last 200 years (VIII).

Let’s limit our focus to just cropland soils, which represent 3.6 billion acres globally (IX). They are estimated to hold 0.12 trillion tons of soil organic carbon, equivalent to 0.45 trillion tons of carbon dioxide (X). This equates to an average concentration of about 1% soil organic carbon across cropland soils (XI).

In nature, we know of multiple ecosystems, such as forests and prairies, and multiple soil types that have accumulated soil organic carbon to levels above 3% at comparable depths (XII), and there is reason to believe that much of today’s croplands had similar levels prior to being cultivated.

Sequestering one teraton of carbon dioxide is possible by increasing the amount of carbon in cropland soil by approximately 0.27 teratons across 3.6 billion acres (XIII). This sequestration would amount to an increase in soil organic carbon levels from 1% to 3% across all cropland, which is in line with the above estimates of the carbon content in many uncultivated soils (IX).**** If grazing and rangeland acres are included in addition to cropland acres, then soil organic carbon levels on these 12B global acres (IX) would only need to rise by approximately 0.5% to sequester one teraton of carbon dioxide (XIV). 

“Soil organic carbon concentration in cultivated soils around the world is so severely depleted that even what water and nutrients are available do not benefit plants as they should,” said Dr. Rattan Lal, professor of soil science with The Ohio State University and director of the Carbon Management Sequestration Center. “Soils depleted of their soil organic carbon stocks have lost their buffering capacity and resilience against uncertain and changing climate. Productive soil requires sufficient
soil organic carbon levels, about 2% by weight in the root zone, and drawing down carbon dioxide is critical not only for enriching agricultural soils – but for addressing climate change and advancing numerous Sustainable Development Goals of the U.N.”

How farms and ranches capture carbon from the atmosphere

Photosynthesis, carried out by plants, and harnessing the energy source of the sun, captures carbon for us naturally. Plants pull carbon dioxide out of the atmosphere and store it in the soil through their roots, and when their biomass is returned to soil, form a collective group of compounds known as soil organic carbon.

Today, we have the opportunity to optimize this natural process through new approaches to agriculture. Specific farming techniques, known as “regenerative growing practices,” have been used by a small percentage of farmers for decades. These techniques increase carbon capture in croplands and drive annual increases in soil carbon. Practices include cover cropping, rotational cropping, reduced or no
tillage, reduced chemical and fertilizer application, and livestock integration – and are just some of the practices we know of today. The ability of regenerative farming practices to increase organic carbon levels in agricultural soils has been well documented across systems that include rotating crops (XV, XVI), cover cropping (XVII, XVIII), integrating crop residue (XIX), reducing tillage (XX), and integrating livestock (XXI, XXII, XXIII), among others.

Regenerative practices should be thought of as any other technology on a farm, like guiding systems for tractors or soil moisture probes. It is a technology with immense societal benefits, available to all farmers today, and just at the beginning of being optimized. And there are dozens of beneficial effects accompanying higher soil organic carbon levels for farmers, like improved resiliency to droughts and floods, higher yielding crops, and more nutritious foods.

“Feeding a growing human population is going to be a challenge unless the global community addresses the global problem of soil degradation,” said Dr. Asmeret Asefaw Berhe, professor of soil biogeochemistry for the Department of Life and Environmental Sciences at University of California, Merced. “And managing soils in a way that maximizes the amount of carbon that they store is one of the most effective ways we can ensure reclamation of degraded soils,” a point she made in

In practice

Indigo began its direct research efforts investigating soil carbon levels in agricultural soils two years ago. We have since collected over 42,000 soil samples from across the U.S., documenting many regenerative growers who have rebuilt their soil organic carbon levels to above 3%, including those in our Indigo Research Partners program, a collection of industry leading farmers who participate in agricultural
technology research and development alongside Indigo.

Within that sample, regenerative growers from Oklahoma displayed soil organic carbon as high as 4%, with over 18% of the total regenerative soil samples collected from the state demonstrating greater than 3% soil organic carbon. Similarly, in Alabama, regenerative growers saw soil organic carbon levels as high as 4%, with over 16% of the total samples collected from the state demonstrating greater than
3% soil organic carbon. One of our grower partners in Minnesota saw soil organic carbon levels reach as high as 6% across 500 regenerative acres, while another in Ohio saw a field with a little over 6%, and an average of 4% soil organic carbon across his whole farm. And this is not just in the U.S. – one grower partner in Ontario, Canada saw soil organic carbon levels of 5.5% across his farm. Through our research and an expansive grower data set, we have been able to identify dramatic increases in soil organic carbon levels within a window of 20 years of regenerative practice implementation.

Of course, those farms represent outliers relative to the diminishing soil carbon levels in conventional agriculture, but we think that is exactly the point. One of our goals at The Terraton Initiative  is to identify the growers and practices who have achieved outstanding results, and then scale those practices across millions of acres.

This is only the beginning of our explorations into soil carbon. Two months ago, Indigo began to sample soil carbon levels down to a one meter depth and collecting other soil health metrics. Over the next 14 months, we will sample more than one million acres of regenerative farms across the country. We’ll return to these same fields every year over the coming decade, while expanding to international geographies, to track changes in soil carbon and other parameters and collaborate with leading scientists and research institutes to publish our observations in peer-reviewed journals. This critical research effort will help us define the rates and potentials of carbon sequestration in soils around the world and design incentives to drive global changes in agricultural practices.

"Soil scientists should equally be cognizant that building soil carbon will likely only be practical through incentives that motivate change in land management, meaning soil science alone will not be adequate to inform decision making,” said Dr. Mark Bradford, researcher and professor within the Yale School of Forestry and Environmental Studies. “For example, incentives will have to address and overcome
difficult social issues, such as where rebuilding soil carbon may improve crop security but only through planting different crops whose value is below the income farmers would have received otherwise."
 

An Innovator's Perspective

Skeptics might point to a number of studies that estimate the total carbon lost from soils at less than a trillion tons, instead ranging anywhere from 350 to 700 billion tons of carbon dioxide (IX). The view that these estimates would represent a maximum for future sequestration is predicated on two assumptions: one, that we can accurately estimate how much carbon has been lost from the soil through history; and two, that the future carbon content of that soil is limited by what it contained in the past. We don’t believe that either premise is true. 

There is no reason to believe that natural ecosystems maximize soil carbon levels, just as they don’t maximize other important attributes such as soil nitrogen levels, yield of seeds, or ears of corn per acre. In at least three studies, researchers have observed carbon stocks of managed agricultural systems to increase by up to two-and-a-half times relative to the levels of those natural ecosystems prior to cultivation (XXIV, XXV, XXVI).

“Regenerative agriculture is comprised of more than twenty specific techniques created by farmers over many decades,” said Paul Hawken, environmentalist, author, and activist. “The past decade has seen extraordinary breakthroughs in practice and productive outcomes, innovative methods that are being tested, analyzed, improved, year after year. Scientists may not fully appreciate what is happening in the soil. Farmers also carry out science—local, observational science of place, crop, weather, soil, disturbance, ruminants, pollinators and more. As the founder of Project Drawdown, we became aware that the peer-reviewed literature around regenerative agriculture was sparse and dated, that it was not broadly sampled and had not studied current practices. What we are seeing is a farm-by-farm revolution that deserves contemporary and thorough analysis.”

Just as 20th century farmers harnessed natural principles to bring corn production to hundreds of bushels per acre, we can optimize carbon capture in agricultural soils. And the farmers cited above are doing it already – and even they are at the very beginning of optimizing performance of regenerative systems. The combination of regenerative practices, incentives for carbon sequestration, and new innovations from around the world presents the opportunity to harness nature and build on it. 

“The scientific community has not yet established whether natural, or unmanaged, ecosystems inherently maximize soil carbon concentrations,” said Dr. Noah Fierer, Professor of microbial ecology at University of Colorado Boulder and a Terraton Initiative research collaborator. “However, we do know that soil carbon concentrations in natural systems typically change slowly and that changes in management practices can accelerate soil carbon storage. We also know that plant productivity, and thus carbon inputs to soil, are often constrained in natural systems and eliminating these constraints could lead to dramatic changes in soil carbon stocks. The Terraton Initiative provides scientists with the unique opportunity to investigate how regenerative agricultural practices could be used to accelerate soil carbon storage, while also improving the sustainability of our agricultural system. We need to be doing this important work, especially given the potential benefits to farmers, consumers, and the environment.” 

An optimistic opportunity

In 2000, experts predicted that we would have 30 gigawatts of wind energy capacity and install one gigawatt of solar power per year by 2010. By 2010, we greatly outpaced those projections, beating them by 14 and 17 times over for wind and solar, respectively (XXVII). Humans are inherently bad at making these kinds of forecasts, in part because the human brain tends to think linearly, rather than exponentially. It is also difficult to forecast when there are exponential increases in the capabilities of technology alongside decreases in the cost of those technologies. 

"Sure, raising soil carbon by a trillion tons is a pretty ambitious goal, but that doesn’t mean we shouldn’t pursue it,” said David Montgomery, author ofGrowing a Revolution: Bringing Our Soil Back to Life. “Even if they only manage to get part way there it would have a major positive impact.  Getting carbon back into agricultural soils can’t be the only thing we do to address climate change, but it’s low hanging fruit that pays dividends. We’d be crazy not to include it on the list of priorities."

Since maximizing soil carbon sequestration has never been attempted before, the upper limit is inherently uncertain. Whether it ends up being more or less than one trillion tons, agriculture represents the most scalable, affordable, and immediate method available to pull carbon dioxide out of the atmosphere – and, through The Terraton Initiative, we are driven to discover and optimize this potential. We are investing in the scientific understanding, public awareness, technological advancements and market-based incentives to push these limits.  This is why the launch of The Initiative in June included The Terraton Experiment, the world’s largest agricultural research study to identify best practices across all regions, geographies, and climates of the world, and a commitment to share that data with other scientific researchers. We also launched The Terraton Challenge to help spur innovation from entrepreneurs and innovators that accelerate the rate of carbon sequestration.

“The Terraton Initiative is an example of how industry can transition science into positive action, and improve the health of the world’s soils at scale. The health of soil, plants, animals, people, and environment is one and indivisible. Eventually, if industry takes the lead, policy makers will follow. I fully support this Initiative,” said Dr. Rattan Lal.

The ability of farmers to store carbon dioxide in their soil is the most optimistic opportunity that we know about with regards to climate change. Of course, that doesn’t mean that it should be our only focus: We must reduce emissions and invest in other ways of pulling carbon dioxide out of the atmosphere, such as planting and preserving forests.  Ultimately, the combination of these activities has the potential to not only reduce the damage that we are causing to our environment, but to reverse it.  We have the ability to do this now; we don’t have to wait for a technical breakthrough. We just have to decide, collectively, that we’re going to make it happen.

Footnotes
* Note: all references to tons are metric tons, not imperial tons.
** 1 ppm of atmospheric carbon dioxide is equivalent to 7.8 billion tons of carbon dioxide.
*** Note: the molecular weight ratio of carbon dioxide to carbon is 44/12, or 3.667.
**** If current levels of carbon in the soil are .12 teratons and add 0.27 teratons of carbon, the net is 0.39 teratons of carbon in the soil. Divided by the total weight of global cropland (14.7 teratons), the result is ~3%.

Citations (Soil Science Society of America Journal style)

I. NOAA Research. 2019. Carbon dioxide levels hit record peak in May. NOAA Research. https://research.noaa.gov/article/ArtMID/587/ArticleID/2461/Carbon-dioxide-levels-hit-record-peak-in-May(accessed 22 Oct. 2019).

II. Riahi, K., A. Gruebler, N. Nakicenovic. 2007. Scenarios of long-term socio-economic and environmental development under climate stabilization. Technological Forecasting and Social Change 74(7):887-935

III. Le Quéré, C., R.M. Andrew, J.G. Canadell, S. Sitch, J.I. Korshakken, et al. 2016. Global Carbon Budget. Earth Systems Science Data 8:605–649.

IV. Jacoby, H.D., and Y.-H.H. Chen. 2014. Expectations for a new climate agreement. Joint Program Report Series Report 264: 1-24.

V. National Academy of Sciences. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. The National Academies Press, Washington, DC.

VI. Lal, R. 2004. Soil Carbon Sequestration Impacts on Global Climate Change and Food Security. Science 304(5677) 1623-1627. 3.

VII. Zomer, R.J., D.A. Bossio, R. Sommer, L.V. Verchot. 2017. Global Sequestration Potential of Increased Organic Carbon in Cropland Soils. Sci. Rep. 7:15554.

Scharlemann, J.PW., E. VJ. Tanner, R. Hiederer, V. Kapos. 2014. Global soil carbon: understanding and managing the largest terrestrial carbon pool. Carbon Management 5(1): 81-91.

VIII. Lal, R. P. Smith, H.F. Jungkunst, W.J. Mitsch, J. Lehmann, et al. 2018. The carbon sequestration potential of terrestrial ecosystems. Journal of Soil & Water Conservation 73:6.

IX. Sanderman, J, T. Hengl, G.J. Fiske. 2017. Soil carbon debt of 12,000 years of human use. Proceeding of the National Academy of Sciences of the United States of America 114(36):9575-9580.

X. Manrique, L, Jones, C. 1991. Bulk density of soils in relation to soil physical and chemical properties. Journal of Soil Science Society America 55:476-481.


XI. Batjes, N.H. 1997. A world dataset of derived soil properties by FAO-UNESCO soil unit for global modelling. Soil Use and Management 13:9-16.

XII. Guo, L.B., and R.M. Gifford. 2002. Soil carbon stocks and land use change: a meta analysis. Global Change Biology 8:345–360.

XIII. USDA Natural Resources Conservation Service. 2008. Soil quality physical indicator information sheet series: bulk density. USDA Natural Resources Conservation Service. https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_053256.pdf (accessed 24 Oct. 2019).

XIV. West, T.O., and W.M. Post. 2002. Soil organic carbon sequestration rates by tillage and crop rotation. Soil Science Society of America Journal 66:1930-1946.

XV. Sainju, U., A. Lenssen, T. Caesar-Thonthat, J. Waddel. 2006. Carbon Sequestration in Dryland Soils and Plant Residue as Influenced by Tillage and Crop Rotation. Journal of Environmental Quality 35.4:1341-1347

XVI. Hubbard, R.K., T.C. Strickland, S. Phatak. 2013. Effects of cover crop systems on soil physical properties and carbon/nitrogen relationships in the coastal plain of southeastern USA. Soil & Tillage Research 126:276-283


XVII. Sainju, U.M., B.P. Singh, and W.F. Whitehead. Long-term effects of tillage, cover crops, and nitrogen fertilization on organic carbon and nitrogen concentrations in sandy loam soils in Georgia, USA. 2002. Soil and Tillage Research 63: 167-179.

XIX. Chalise, K.S., S. Singh, B.R. Wegner, S. Kumar, J. D. Perez-Gutierrez, et al. 2018.Cover Crops and Returning Residue Impact on Soil Organic Carbon, Bulk Density, Penetration Resistance, Water Retention, Infiltration, and Soybean Yield. Agronomy Journal111: 99-108.

XX. Varvel, G.E., and W.W. Wilhelm. 2010.Long-term soil organic carbon as affected by tillage and cropping systems. Soil Science Society of America Journal 74(3): 915-921.

XXI. McSherry, M.E., and M.E. Ritchie. 2013., Effects of grazing on grassland soil carbon: a global review.Global Change Biology 19(5): 1347-1357.

XXII. Teague, W.R., S. L. Dowhower, S.A. Baker, N. Haile, P.B. DeLaune, et al. 2011.Grazing management impacts on vegetation, soil biota and soil chemical, physical and hydrological properties in tall grass prairie.Agriculture, Ecosystems & Environment 141(3-4): 310-322.

XXIII. Chaplot, V., P. Dlamini, and P. Chivenge. 2016. Potential of grassland rehabilitation through high density-short duration grazing to sequester atmospheric carbon. Geoderma 271: 10-17.

XXIV. Su, Y.Z., X.F. Wang, R. Yang, J. Lee. 2010. Effects of sandy desertified land rehabilitation on soil carbon sequestration and aggregation in an arid region in China. Journal of Environmental Management 91:2109-2116.

XXV. Li, X.G., Y.K.Li, F.M. Li, Q. Ma, P.L. Zhang, P. Yin. 2009. Changes in soil organic carbon, nutrients, and aggregation after conversion of native desert soil into irrigated arable land. Soil & Tillage Research 104:263-269.

XXVI. Mendham, D.S., A.M. O’Connell, T.S. Grove. 2003. Change in soil carbon after land clearing or afforestation in highly weathered lateritic and sandy soils of south-western Australia. Agriculture Ecosystems & Environment 95: 143-156.

XXVII. Gore, Al, T.H. Ha, K.T. May. 2016. Why Al Gore feels optimistic about climate change. TEDBlog.