Farmers are being paid millions to trap carbon in their soils. Will it actually help the planet?

 

Lance Unger has been implementing some changes on his farm near the Wabash River in southwestern Indiana. Instead of leaving his fields fallow after the harvest, he planted cover crops of oats and sorghum that grew until winter. Before planting corn and soybeans in the spring, he used a machine to remove last season's stalks, rather than tilling the soil and plowing them under.

In recognition of these efforts, a Boston-based company called Indigo paid Unger $26,232 in late 2021 and an even larger sum last year. This payment reflects the value that the emerging market places on the hundreds of tons of carbon that Unger, in theory, pulled out of the atmosphere with his cover crops or retained in the soil through reduced tilling. While slowing climate change is not his primary goal, Unger acknowledges that the financial benefits made the changes worthwhile for him. "I need to see economic benefits," he says.

The deal was also profitable for Indigo, which took a 25% cut of the carbon credits bundle and sold them at approximately $40 per ton of captured carbon. The buyers of these credits included companies such as IBM, JPMorgan Chase, and Shopify, seeking to offset greenhouse gas emissions from their operations and enhance their environmentally friendly reputation.

For advocates, this exchange exemplifies a promising fusion of idealism and capitalism to address the pressing issue of climate change. If implemented on a global scale, soil-based carbon capture has the potential to offset between 5% and 15% of greenhouse gas emissions annually, according to a influential 2004 study by Rattan Lal, a soil scientist from Ohio State University. Deborah Bossio, lead soil scientist for the Nature Conservancy, shares this optimism, expressing confidence in the ability to build carbon in soil.

Millions of dollars worth of soil credits have already been sold, and companies like Indigo are aggressively expanding to seize a share of the industry, which is projected to be worth $50 billion by 2030, according to consulting firm McKinsey & Company. With other carbon markets based on tree planting or preservation facing criticism for offering questionable or fraudulent credits, some buyers may view soil-based credits as a safer option.

However, as the industry gains momentum, so does the skepticism. Some researchers argue that the science behind how soils store and release carbon is too uncertain to fully support an industry claiming to have a significant cooling effect on the planet. They accuse companies like Indigo of exaggerating the benefits of their programs.

"I believe the eagerness has somewhat distorted the vision of what is truly feasible," says Ernie Marx, a soil scientist who retired from Colorado State University (CSU) in 2021 and worked for over a decade on the computer model used by Indigo and other companies to calculate carbon credits. Emily Oldfield, a soil scientist with the Environmental Defense Fund, who has examined soil-based carbon markets, also harbors doubts, stating that evaluating the actual greenhouse gas benefits of these programs is extremely challenging.

However, one fact remains indisputable: Modern agriculture has not been beneficial for soils or the climate. Over thousands of years, microbes converted some carbon from decaying trees and plants into long-lasting forms, contributing to the development of fertile soils worldwide. Yet, since humans began plowing and disturbing soils around 12,000 years ago, an estimated 116 billion tons of carbon have been lost—either eroded by wind and water or released into the atmosphere as carbon dioxide (CO2) by microbes, as reported in a 2017 study.

Regenerative practices aim to build and protect soil carbon rather than deplete it. Major food corporations like General Mills, Land O'Lakes, and Cargill have embraced this movement, claiming to reduce the climate impact of their supply chains by incentivizing farmers to adopt regenerative tactics. The U.S. government is also investing billions of dollars into what it terms "climate-smart agriculture."

A meta-analysis of data from experimental plots published in May offered positive findings. It indicated that both no-till and cover cropping increased topsoil carbon by an average of over 11%. However, it was noted that these practices needed to be applied for at least 6 years to achieve significant gains.

Modern agricultural practices have taken a toll on soil health, resulting in the loss of billions of tons of carbon, either released into the atmosphere or eroded away. However, regenerative practices offer a solution by improving soil health and effectively storing carbon, which can help slow down climate change. These practices also create valuable carbon credits that can be sold. Yet, accurately calculating the exact benefits of these regenerative practices remains a complex challenge.

While regenerative farming practices show promise in increasing soil carbon levels and slowing climate change, recent findings have brought some caution to the enthusiasm. Studies reveal that while reduced tillage may lead to carbon accumulation in the topsoil, deeper soil layers may experience offsetting losses as crop residues decompose on the surface. Additionally, off-season cover crops can sequester carbon in the soil, but practical challenges, such as planting complications and cold weather in certain regions, limit their widespread adoption.

The lack of a reliable method to quantify soil carbon gains and measure nitrous oxide emissions further complicates efforts to commercialize soil carbon credits. Some companies have faced criticism for their approaches, with concerns raised about the validity and transparency of carbon markets. In contrast, Indigo, a privately held company that entered the soil carbon credit business in 2019, is working with a third-party registry and utilizing soil cores and an academic computer model to estimate climate benefits accurately.

The model, originally launched in the 1980s and called Century, was designed to simulate soil carbon dynamics on long timescales of a century or more. As concerns about climate change grew, the researchers sought to enhance the model to account for the exchange of greenhouse gases like CO2, methane, and N2O between the air and land during a growing season. This led to the development of DayCent, one of the world's leading soil models. DayCent is widely used in climate change forecasting and environmental reporting.

However, despite its prominence, DayCent has its limitations. It does not fully represent the complexities of soil processes, such as microbial interactions and carbon respiration, relying instead on estimated gains and losses of soil carbon based on published experimental data. Moreover, accurately accounting for N2O emissions from soil microbes has proven challenging. The model's calibration and validation depend on data from a limited number of field trials, which may not fully capture the diversity of real-world farming conditions.

These limitations result in uncertainties in the model's output, especially for smaller regions. Studies have shown that the uncertainties could exceed 100%, making it difficult for the model to accurately determine whether soil carbon has increased or decreased over time in certain areas. The researchers recognize the need for more data and continuous improvements to enhance the model's accuracy and reliability.

However, some researchers from Colorado State University (CSU) and their sponsors at the USDA wanted to make DayCent modeling more accessible to the public. In the early 2010s, they released COMET-Farm, a web tool based largely on DayCent, which allowed farmers to input information about their fields and proposed changes in farming practices to estimate the amount of carbon they could sequester.

As interest from companies in using DayCent and COMET-Farm for carbon markets grew, concerns about the model's uncertainties were often overlooked, leading to what some described as a "gold rush mentality." In response to the demand, CSU's modeling team founded a company called Soil Metrics, providing commercial access to DayCent. Companies like Nori and Indigo became clients, and in 2021, Indigo acquired Soil Metrics, with one of the CSU researchers, Keith Paustian, becoming a consultant for the company.

Around the same time, the CSU researchers initiated a new project to better quantify the model's uncertainties. However, the team found that the uncertainties were still too significant to determine whether specific changes in farming practices had a positive or negative impact on the climate. The results of this project were never published, and the COMET-Farm interface continues to state that methods for estimating uncertainty are still under development.

Adam Chambers, a USDA program officer overseeing DayCent and COMET-Farm, admitted that the uncertainty analysis proved to be more challenging than expected, and they reached the limits of current scientific understanding. Additionally, a confidential draft document shared by Chambers revealed that DayCent's results were not only uncertain but also biased, leading to exaggerated estimates of carbon storage for soils with higher carbon levels. Chambers mentioned that it could take years to understand and correct this bias.

In the meantime, Ogle points out that the bias in the model means the climate benefits of regenerative practices may not be as significant as estimated, though likely still positive. He admits that the CSU team has not adequately reported the uncertainties to farmers, policymakers, and other stakeholders, acknowledging the need for improvement.

Marx, on the other hand, believes that the CSU team intentionally obscured the model's shortcomings. In early 2021, he filed a complaint alleging that the uncertainty results had been suppressed, leading to an investigation. However, the university dismissed Marx's complaint, but the investigation committee criticized the team for claiming results were "accurate" in the COMET-Farm interface.

Those involved in the soil carbon credit markets are aware of the limitations of DayCent and COMET-Farm. The lack of uncertainty estimates is concerning to some experts, as they believe a high level of certainty is essential in transactional markets. Additionally, questions are raised about the 100-year permanence claim of credited carbon by companies like Indigo, as maintaining regenerative practices for such a long duration is uncertain.

Indigo is making efforts to reduce uncertainties in the model by using a new "Bayesian" method to identify and tune the most crucial model parameters based on experimental data. They also account for uncertainties by reserving 14.5% of the credits in a "buffer pool" to address potential carbon losses due to natural disasters. Indigo aims to provide reasonably accurate estimates by merging measurements and modeling, even though the overall approach is not considered perfect, it is considered to make sense by some experts.

As the soil carbon credit industry continues to grow, addressing the uncertainties and limitations in the models will be crucial to ensuring the credibility and effectiveness of these initiatives in mitigating climate change.

And the company is actively conducting the research needed to strengthen such initiatives. In a farm near Arcadia, Indiana, a cover-cropped field and a bare one were observed in April, with Indigo funding a crew to pull out soil cores to measure the carbon buildup in the cover-cropped field. Additionally, a solar-powered flux tower measures CO2 exchange in the soil every 100 milliseconds. These efforts are part of an extensive soil carbon experiment launched by Indigo in 2019, along with its offset program. The U.S. Department of Agriculture (USDA) has also pledged to invest $300 million in a network of soil-monitoring sites across farmland, further supporting such initiatives.

Indigo's leaders emphasize that while these studies will add confidence, waiting for results before launching their marketplace would cause unacceptable delays in addressing climate change. The company has already paid millions to hundreds of farmers for adopting regenerative practices, with plans to expand the program to millions of hectares next year.

However, for soil carbon capture programs to succeed, they will require the support and participation of thousands of farmers willing to embrace new practices. Early adopters like Unger offer both optimism and caution. While he appreciates working with Indigo and the payments received, he also acknowledges that farmers face uncertainties, and not all practices may be profitable or feasible for every field or situation. He advises against overselling regenerative agriculture, as real-world challenges, such as weather and market conditions, can impact the success of these practices.

In the end, achieving widespread adoption of soil carbon capture programs will require a nuanced understanding of the complexities and realities faced by farmers, as well as continuous research and improvement in these initiatives. The aim is to find practical solutions that align with farmers' existing goals and values while contributing positively to climate change mitigation.