A biochar designed for carbon removal may not deliver the same soil benefits
A material born from ancient agricultural practice is now being asked to carry the weight of two distinct promises — healing degraded soils and sequestering carbon for centuries — but new research published in the journal Biochar cautions that these are not the same ambition, and may not be achievable from the same product. The temperature at which biochar is made determines whether it becomes a durable carbon vault or a biologically active soil amendment, and conflating the two in voluntary carbon markets risks misallocating the very resources meant to address climate change. As biochar moves from niche practice to global climate instrument, the field faces a foundational reckoning: precision and honesty in labeling may matter as much as the material itself.
- Biochar is entering global carbon markets with two competing identities — climate solution and soil enhancer — but the science says these goals often require fundamentally different products made at different temperatures.
- High-temperature biochar locks carbon away for centuries but becomes chemically inert, losing the reactive surface properties that make soil biology thrive; low-temperature biochar feeds the soil but releases its carbon too quickly to count as durable sequestration.
- Inconsistent reporting of feedstock type, pyrolysis temperature, and chemical ratios is already enabling overstated climate and agricultural claims, threatening the credibility of carbon credit systems that depend on verifiable outcomes.
- Researchers are calling for a 'designer biochar' framework — products engineered and transparently labeled for a single purpose, whether carbon removal or soil health, rather than marketed as a universal fix for both.
- The stakes are rising: as biochar carbon credits expand globally, the gap between what is promised and what is delivered could redirect billions in climate finance toward outcomes that were never scientifically guaranteed.
Biochar — carbon-rich char produced by heating plant waste in low-oxygen conditions — is being promoted simultaneously as a climate solution and a soil enhancer. But a new perspective in the journal Biochar argues that these two promises are fundamentally in tension, and that the confusion is beginning to carry real consequences.
The core problem is thermodynamic. Higher pyrolysis temperatures produce biochar that is chemically stable enough to store carbon for centuries, but that same stability makes the material inert — less able to interact with soil biology, hold nutrients, or support microbial communities. Lower-temperature biochar retains the reactive surface chemistry that benefits soil health, but it degrades faster, meaning the carbon doesn't stay sequestered for long. These are not the same product, even when they look identical and share a name.
Lead author Robert W. Brown and colleagues warn that as biochar enters voluntary carbon markets — where companies purchase credits to offset emissions — the distinction is being lost in marketing language. Farmers are told biochar will improve their soil and help the climate. Carbon credit buyers are told it will remove CO2. Both claims might be true, but not necessarily from the same batch. Without transparent reporting of feedstock type, pyrolysis temperature, and key chemical ratios, there is no reliable way to verify which promise a given product can keep.
The authors also note that context shapes outcomes: degraded and tropical soils respond more strongly to biochar than productive temperate soils, and more stable biochars can be enhanced through composting or microbial inoculation — though at added cost and complexity.
What they are calling for is a 'designer biochar' approach: products engineered and honestly labeled for a specific purpose, with consistent reporting standards that allow buyers and regulators to hold claims accountable. As biochar moves toward the center of global climate strategy, the field's credibility will depend on learning to distinguish — and communicate — what this material can genuinely do for the soil versus what it can do for the atmosphere.
Biochar—that carbon-rich char made by heating plant waste in low-oxygen conditions—is having a moment. It's being promoted as a climate solution, a soil enhancer, sometimes both at once. But a new perspective in the journal Biochar argues that we've been conflating two fundamentally different things, and the confusion is starting to matter.
The problem is this: biochar designed to lock carbon away for centuries doesn't necessarily make soil better. And biochar that makes soil better might not lock carbon away for centuries. These are not the same product, even though they look similar and come from the same basic process. Yet as biochar enters voluntary carbon markets—where companies buy credits to offset emissions—the distinction is getting lost in marketing language and loose claims.
Robert W. Brown, the lead author of the perspective, puts it plainly: a biochar engineered for durable carbon removal may not deliver the same soil benefits as one designed as a soil conditioner. The difference comes down to how hot you heat the feedstock. Higher temperatures produce biochar that's more chemically stable, better at storing carbon for the long haul. But that stability comes at a cost—the material becomes more inert, less reactive with soil biology and chemistry. Lower-temperature biochar retains more surface functional groups, the chemical hooks that help soil hold onto nutrients and water, support microbial communities, and stabilize pollutants. But it degrades faster, which means the carbon doesn't stay locked away as long.
This matters because the two goals are increasingly being marketed as one. Farmers are told biochar will improve their soil and help the climate. Carbon credit buyers are told biochar will remove CO2 from the atmosphere. Both things might be true, but not necessarily from the same batch of biochar. Without knowing the feedstock type, the pyrolysis temperature, and the resulting chemical ratios—the hydrogen-to-carbon and oxygen-to-carbon numbers that define the material—it's impossible to know which promise a given product can actually keep.
The authors argue that inconsistent reporting is already creating problems. Claims about climate benefits and agricultural co-benefits are becoming overstated or misleading. As biochar carbon credits expand globally, this confusion could lead to serious misallocation of climate resources—money spent on biochar that doesn't actually do what was promised.
Context matters too. Degraded soils and tropical soils show stronger responses to biochar than productive temperate soils do. And there are ways to enhance the soil benefits of more stable biochars—composting it, blending it with fertilizer, inoculating it with microbes—but these steps add complexity and cost.
What the authors are calling for is a shift toward what they call "designer biochar." Instead of marketing one product as a universal fix, biochar should be engineered and labeled for specific purposes. A product meant for carbon removal should be transparent about its carbon stability and realistic about soil benefits. A product meant for soil health should be honest about its carbon durability. The feedstock, temperature, and chemical properties should be reported consistently, so buyers and regulators can actually verify the claims.
As biochar moves from the margins into mainstream climate strategy, this distinction will only become more important. Trust in carbon markets depends on credible science and honest labeling. Right now, the field is still learning to tell the difference between what biochar can do for the soil and what it can do for the climate. The next phase will be designing products that do one or the other well, rather than promising both.
Notable Quotes
A biochar designed for durable carbon removal may not deliver the same soil benefits as one designed as a soil conditioner. Recognizing this distinction is essential for credible science, policy, and carbon markets.— Robert W. Brown, lead author
The Hearth Conversation Another angle on the story
Why does the temperature at which you make biochar matter so much?
Temperature determines stability. High heat creates a more condensed, aromatic structure—basically, carbon that's locked into a form that resists decomposition. Low heat leaves more of the original plant material's chemistry intact, which means more reactive surfaces. Those surfaces are what make soil better, but they're also what makes the biochar vulnerable to decay.
So you're saying we have to choose. Better soil or better carbon storage?
Not entirely. But the trade-off is real, and it's not being acknowledged clearly enough. A farmer and a carbon credit buyer might both be buying "biochar," but they need different things.
What happens if we just keep selling the same biochar for both purposes?
You get broken promises. The farmer's soil doesn't improve as much as expected. The carbon credit buyer's offset doesn't last as long as claimed. And the whole market loses credibility.
Is there a way to make biochar that does both well?
Possibly, with activation—composting it, adding microbes, blending it with nutrients. But that costs more and requires more expertise. It's not the simple story that's being sold right now.
What would change if companies had to report the actual chemistry of their biochar?
Everything. You'd know exactly what you were buying. You couldn't hide behind vague claims. The market would have to become honest about what each product actually does.
And if that doesn't happen?
Climate resources get wasted on biochar that doesn't deliver. Trust in carbon markets erodes. The whole field gets tainted by overpromising.