It’s a Dirty Job: Translating Soil Carbon into Reliable Carbon Credits

Converting the excess 750 billion tons of atmospheric carbon into functional soil reserves is one goal of the voluntary carbon market.

When it comes to climate change, carbon is most often thought of in its’ atmospheric, gaseous  form. And, even though atmospheric carbon dioxide levels have gone up dramatically, soil actually holds two times as much carbon as the atmosphere - containing around 1,500 billion tons in total. 

Holding carbon in soil as soil organic carbon (SOC) is incredibly useful. It’s a natural precursor to economic activities like farming, forestry & the creation of all sorts of natural capital. And, unlike atmospheric carbon, losing carbon in soil makes climate change worse, contributing to floods, drought, and other extreme weather. That’s because SOC helps create an ecological sponge that insulates the landscape. 

Stream before passing through a carbon project area focused on managed grazing. Eroded creek walls help create a lack of SOC in the landscape & diminishing natural capital.

Carbon credits offer larger incentives for producers to invest in creating & maintaining soil based carbon. Payments add financial and technological resources that can enable better results. 

Funding soil carbon restoration is also considered a nature based solution to climate change. Nature based solutions leverage ecology to sequester carbon via activities like planting trees, restoring wetlands,and improving soil health. One shortcoming of accounting just for changes in soil carbon is the potential to miss other value created by Nature Based solutions; however producers may be able to directly account for co-benefits like resilience, biodiversity, and higher net productivity in their bottom line. 

Generally, the formula works like this:  

Carbon Credits = (Deliberate Change in Soil Carbon – Normal Change in Soil Carbon) + (Normal Baseline Emissions – Deliberate Project Emissions)

Nature based offsets reward land managers who pump carbon back into living systems under this formula. Different on-farm and land management practices can convert atmospheric carbon  into soil carbon. One of these practices is a focus for Kateri: Managed Grazing. 

Managed Grazing is ranked by Project Drawdown as having the potential for 16.24 gigatons of Carbon reduction; or roughly the ability to sequester all of the annual emissions of the entire fortune 500 (circa 2018, totalling ~13 gigatons). 

With managed grazing, animals can have the effect of changing the biological and chemical structure of grasslands’ soil. These changes allow the soil to absorb more water during rainfall events and stimulate growth cycles for increased SOC. For active day-to-day management under this practice change, two things matter most - how long a quantity of animals graze a specific area and how long to wait until they return. Kateri tracks animal movement to provide this feedback to producers & to help certify carbon yields as a result of management. Early results from one such project in New Mexico are depicted below. 

Stream after passing through a carbon project area focused on managed grazing holds more moisture and vegetation, partly from increased SOC levels.

The Challenge of Measuring Nature-Based SOC

Ecological systems, including farming and ranching, have highly variable carbon flows that are impacted by weather, species, and soil types, and more. How long the carbon will stay removed from the atmosphere depends on the local climate, too. SOC - unlike some other forms of carbon sequestration - has a level of permanence that varies across different ecologies and land use practices. It can also be reversed with ground disturbance. 

That’s part of why when issuing carbon credits, SOC changes must be considered from a baseline scenario. This baseline covers the living systems’ normal carbon flows alongside changes that new management bring. For most  of Kateri’s projects, this means understanding how grass grows, is consumed, dies, and regenerates in relationship to its’ exposure to grazing animals. We try to optimize this cycle for carbon creation & active soil building efforts. 

Quantifying the extra carbon producers may create requires a combination of understandings.  What changed in the landscape, features from the local climate help fuel process - based modeling, and the extraction of these attributes for verification purposes. Together, these efforts combine to determine producers’ rewards.

Annual SOC changes in natural systems are better understood over time as a function of weather & management

The Importance of Soil Sampling, Today  

Soil sampling plays a critical role for determining the baseline SOC levels across project landscapes, providing inputs for process based models, and tuning in ongoing ground-truthing. In the future, technology may replace any need for digging, but today, the Soil Health Institute recommends measuring SOC using a method called dry combustion. 

Under dry combustion, soil samples are pre-treated to remove inorganic carbon and then burned inside special equipment while measuring the gasses released to determine the percentage of SOC in each sample. This figure is then combined with soil bulk density measurements to get total carbon stock in each sample. 

For this soil sampling effort, Kateri works with Yard Stick PBC for stratification, sample plan design, lab qualification, field work, lab data reporting/QC, and final stock quantification.  These data are used as inputs for process based modeling to specify changes in SOC and determine carbon credit payments.

“At Yard Stick, we’ve committed to making soil sampling less of a barrier to carbon credit issuances by providing a cost-effective, streamlined service to customers seeking ground truth data to back up crediting claims. Over time, these data will to help us build out robust, low cost spectral soil SOC measurement technologies which can expand market access & overall impact” 

• Chris Tolles, CEO Yard Stick 

For producers in their program, Kateri works with Yard Stick to take a meter deep soil sample every 5 years to track SOC stock changes. In the interim years, process based modeling uses the latest values from these sampling efforts as key inputs to help determine credit payments. 

Once a carbon project is baselined, soil sampled, and run through process based models, credit buyers - like Kateri’s partner Shell - can access and buy blocks of credits. Because of the living system’s variability related to these SOC accumulations, features like insurance pools & conservative accounting add to the certainty that soil sampling and process based modeling help provide. 

Over time, performing sensitivity analysis looking back at process-based modeling should help examine which parameters, including soil samples, create the best predictions for SOC outcomes. This may ease reporting burdens on all parties and help narrow and focus reporting requirements. 

These intensive steps currently reduce credit profitability & may limit eligible landowners who can meaningfully jump the bureaucratic moat. Still, Parcel aggregation, as well as possible price increases in carbon payments, hold promise to deepen the impact of carbon markets & further natural capital development. 

Developing the Future of SOC Measurement with Remote Sensing 

Though technology can already effectively measure aspects of natural capital as a service, more change is underway. 

Some companies, like Earth Optics’ new partner Trace Genomics aim to map soil biology at the microscopic level while others like Planet Labs promise daily images of the whole earth. Kateri uses satellite based datasets furnished by the US government to map out Net Primary Productivity and other landscape functions prior to entering carbon contracts with producers. 

Companies like Perennial are also taking a unique approach toward modeling soil carbon. Instead of a process-based model, Perennial’s technology utilizes geospatial data combined with physical soil samples, and machine learning to model SOC stocks and changes directly. Each additional soil sample is added to Perennial’s extensive sampling library &  improves their SOC modeling capabilities. These results can being localized to any field, farm, ranch, or county for improved accuracy and sensitivity. Perennial’s solution is built to scale by driving down soil costs for project developers looking to create high precision and validated carbon credits. 

 "Mapping carbon in soils using satellite technology greatly reduces the need for on-the-ground soil samples and drives down cost. This is good for growers and good for transparency in carbon accounting."

•  Chief Scientist, Dr. James Kellner - Perennial 

If we look around the effort of translating soil carbon into reliable carbon credits, we see numerous signs of progress like this. Ground-truthed datasets combined with AI are further reducing the cost of assessing and rewarding landscape scale ecological outcomes. Regulators and private markets are starting to set standards for myriad carbon projects for these systems to assess. Producers are starting to experiment with farming techniques that can produce meaningful revenue. And more. It’s a long - but fast - road ahead.