Biochar’s carbon storage potential undervalued due to outdated assessment methods, study finds

Biochar, a charcoal-like material derived from plant biomass, has long been hailed as a promising tool for carbon dioxide removal. However, a new study by Stanford researchers highlights a critical issue: current methods for assessing biochar’s carbon storage potential may significantly undervalue its true environmental benefits.

The paper, published in Environmental Research Letters points the way to more accurately evaluating biochar, and boosting its credibility as a climate change solution.

The research challenges conventional durability metrics and proposes a more nuanced framework for evaluating biochar projects. It grew out of an early project looking at soil’s ability to capture carbon dioxide.

“We realized that even though biochar is really important component of the carbon removals market, there is very little useful data on how it actually behaves,” said study co-author Kate Maher, a professor of Earth system science in the Stanford Doerr School of Sustainability and a senior fellow at the Stanford Woods Institute for the Environment. “It is important for policymakers and buyers to be aware of this.”

Rethinking biochar durability

Biochar is the charcoal-like result of burning organic matter slowly with little oxygen. Its appeal lies in its ability to store carbon in soil for extended periods, preventing it from re-entering the atmosphere as a greenhouse gas. The durability of biochar—its resistance to decomposition—is a key factor in determining its effectiveness.

However, most biochar durability assessments rely on a single metric: the hydrogen-to-carbon ratio. This simple measure is thought to correlate with biochar’s stability in soil, but the Stanford study reveals that this approach might be too reductive.

By reanalyzing the largest existing biochar durability dataset, the researchers uncovered that relying solely on hydrogen-to-carbon ratios ignores critical factors such as soil type, environmental conditions, and biochar feedstock variability. Without these factors, models often fail to predict real-world outcomes for carbon storage and benefits to soil health and crops.

“Biochar has immense potential for carbon dioxide removal, but it will be viewed as less valuable by the market until we can confidently establish and predict its long-term durability,” said study co-author A.J. Ringsby, a chemical engineering Ph.D. student in the Stanford School of Engineering. “To get to a place where biochar stacks up against highly durable solutions like direct air capture, we need to move beyond one-size-fits-all metrics and do the ground work to develop more useful datasets.”

The study also found that current standards may underestimate the carbon storage potential of many biochar projects. Laboratory experiments, often the basis for durability assessments, are more tractable but often fail to accurately replicate real-world conditions. For instance, field studies show that factors like soil composition and local climate can drastically influence how biochar behaves once deployed.

Undervaluing biochar’s durability potentially leaves a substantial amount of carbon storage uncredited. This could create economic and policy challenges, especially as the demand for carbon offsets grows.

Towards a smarter future

To address these shortcomings, the researchers propose a two-step evaluation process: a preliminary estimate of biochar’s potential to remove carbon dioxide before deployment, followed by field measurements to refine these estimates over time. This approach, they argue, could unlock additional project value, improve data for predictive modeling, and enhance the credibility of biochar in carbon markets.

The study also underscores the need for coordinated global field trials to better understand how environmental variables influence biochar performance. These trials could inform new durability standards that account for real-world variability, paving the way for more accurate carbon crediting.

“Unlike most technologies in the market, biochar is shovel-ready and delivering carbon removal today,” Ringsby said. “To unlock its full potential, we need better data, stronger standards, and to work together as a community to design the right experiments.”