Biochar

Also known as Biochar carbon removal, BCR

Biochar is a carbon-rich solid made by heating biomass with little or no oxygen, which can be added to soil to store carbon for a long time. Field and laboratory evidence suggests much of its carbon persists for decades or longer, but yield effects vary widely by region and soil, and credited volumes are reported inconsistently.

CommercialDemonstratedReviewed 21 Oct 2026
AI illustration · Illustrative scene, not a photograph of the specific device or experiment.

In plain language

Biochar is a kind of charcoal made by heating plant material, such as crop residues or wood, in a low-oxygen environment. The heating turns the material into a stable, carbon-rich solid. When biochar is mixed into soil, much of its carbon can stay there for a long time, which is why it is studied as a way to remove carbon from the air and keep it stored.

The open questions are how long the carbon really stays, and what biochar does to crop yields. Results vary. Some studies find yield gains, especially on poor tropical soils, while trials in cooler regions often show little change. Carbon removal credits for biochar have been contracted in large volumes, but reported totals differ between sources, and the models that estimate how long the carbon lasts rest on a limited number of studies.

Technical explanation

Biochar is produced by pyrolysis, which heats biomass at high temperature with little or no oxygen. Long-term storage is usually assessed with decomposition studies that use isotope labelling (stable 13C or radioactive 14C) to separate biochar carbon from the soil's own organic carbon.

Wang, Xiong and Kuzyakov (2015) pooled 128 decomposition observations from 24 studies and fitted a two-pool model. The model assigns about 3% of biochar carbon a mean residence time of roughly 108 days and about 97% a residence time of roughly 556 years. The long-term figure is a model output, not a direct measurement, and it depends on the 24 studies included. The same authors' priming analysis of 116 observations from 21 studies reports an overall mean effect of -3.8%, with a 95% confidence interval of -8.1% to 0.8%, which spans zero.

Yield evidence comes from meta-analyses of field trials. Jeffery and colleagues (2011) reported a grand mean increase in crop productivity of 10%, with individual analyses ranging from -28% to 39%, and found that results depended on soil properties and experimental set-up. A 2017 meta-analysis by Jeffery and colleagues found no average yield effect in temperate latitudes and about a 25% average increase in the tropics, which the authors link to liming and fertilisation. Carbon credits are issued under registry methodologies, but those methodology documents were not read for this profile, so the detailed permanence and measurement rules are not described here.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Demonstrated Shown in a published experiment, test or shipping product.

Wang, Xiong and Kuzyakov (2015) pooled 128 decomposition observations from 24 studies that used isotope-labelled carbon, and fitted a two-pool model in which about 3% of biochar carbon has a mean residence time of roughly 108 days and about 97% has a residence time of roughly 556 years.

Sources: [2] · Abstract · medium confidence

The authors of the 2015 meta-analysis state that current knowledge of the degradability of biochar is limited.

Sources: [2] · Abstract

In a separate analysis of 116 observations from 21 studies, biochar gave an overall mean priming effect of -3.8% on soil organic matter mineralisation, with a 95% confidence interval of -8.1% to 0.8%, so the effect is not clearly different from zero.

Sources: [2] · Abstract · medium confidence

Jeffery and colleagues (2011) found a grand mean increase in crop productivity of 10% from biochar, with individual analyses ranging from -28% to 39%.

Sources: [3] · Abstract

The 2011 meta-analysis reports that the yield results are variable and depend on the experimental set-up and soil properties, that only short-term studies of one to two years were available, and that biosolids were the only feedstock with a statistically significant negative effect.

Sources: [3] · Abstract

Jeffery and colleagues (2017) report that biochar has, on average, no effect on crop yield in temperate latitudes, and an average 25% yield increase in the tropics, which they attribute to liming and fertilisation.

Sources: [4] · Abstract summary · medium confidence

Reported, unverified Stated by a company or team but not independently confirmed.

Puro.earth reported 1 million carbon removal certificates issued by March 2025, with biochar accounting for 34.1% of those issuances.

Sources: [6] · Article text · medium confidence

CDR.fyi reports 3.04 million tonnes of biochar carbon removal credits contracted between 2022 and the first half of 2025, but its delivered totals differ between its summary (658 thousand tonnes) and its body text (683 thousand tonnes).

Sources: [5] · Highlights and body text · medium confidence

Proposed A design or plan that has not yet been built or tested.

Woolf and colleagues propose soil storage of biochar as a means of abating climate change by sequestering carbon, and state that substantial uncertainties exist about its impact, capacity and sustainability at the global level.

Sources: [1] · Abstract

Limitations and open problems

  • Permanence estimates rest on a model fitted to 24 isotope studies, and Wang and colleagues (2015) state that current knowledge of biochar degradability is limited.
  • Yield effects are inconsistent: Jeffery and colleagues (2011) report a range from -28% to 39%, and the authors note that only short-term studies of one to two years were available.
  • Temperate-zone benefits are not shown on average, so gains depend heavily on region and soil (Jeffery and colleagues, 2017).
  • Feedstock matters: in the 2011 analysis, biosolids were the only feedstock with a statistically significant negative yield effect.
  • Reported credit volumes are inconsistent. CDR.fyi gives different delivered and retired totals in its highlights and body text, and the sources reviewed here do not give a verified biochar-only certified total.

Possible future uses

Speculative

Ideas, not predictions. None of these has been demonstrated.

  • Biochar blended into growing media for indoor or vertical farms, where soil conditions can be controlled and nutrient losses kept low.
  • On-farm biochar made from crop residues to close nutrient loops, with any carbon credits kept on the same farm.
  • Targeted use on acidic tropical soils, where liming and fertilisation effects are largest, rather than as a general soil treatment.

Timeline

  1. 2010Woolf and colleagues publish 'Sustainable biochar to mitigate global climate change' in Nature Communications, estimating the sustainable technical potential of soil storage of biochar to mitigate climate change. Sources: [1]
  2. Nov 2011Jeffery and colleagues publish a meta-analysis in Agriculture, Ecosystems & Environment finding a grand mean 10% increase in crop productivity. Sources: [3]
  3. Apr 2015Wang, Xiong and Kuzyakov publish a meta-analysis in GCB Bioenergy estimating biochar mean residence times from 24 isotope studies. Sources: [2]
  4. 2017Jeffery and colleagues publish in Environmental Research Letters that biochar has no average yield effect in temperate latitudes and about a 25% average increase in the tropics. Sources: [4]
  5. Mar 2025Puro.earth reaches 1 million carbon removal certificates issued, with biochar accounting for 34.1% of those issuances. Sources: [6]
  6. Sept 2025CDR.fyi reports that 3.04 million tonnes of biochar carbon removal credits were contracted from 2022 to the first half of 2025. Sources: [5]

Futures this could help bring about

AI illustration
How far away?

Biochar as mainstream carbon removal

Scaling up · 2 of 7 steps done

AI illustration
How far away?

Buildings that lock away carbon

Pilots · 2 of 6 steps done

Related breakthroughs

Glossary

Pyrolysis
Heating a material at high temperature with little or no oxygen, so that it breaks down into a solid, liquid and gas without burning.
Mean residence time
The average time a carbon atom stays in a pool, such as soil, before it is lost to the atmosphere.
Priming effect
A change in how fast existing soil organic matter breaks down after fresh carbon, such as biochar, is added to the soil.
Carbon removal credit
A certificate that represents a tonne of carbon dioxide removed from the air and stored, which can be sold to buyers who want to offset emissions.

Sources

  1. peer reviewed paper
    Sustainable biochar to mitigate global climate change
    Woolf D, Amonette JE, Street-Perrott FA et al.. Nature Communications, 10 Aug 2010. DOI: 10.1038/ncomms1053. Accessed 21 Oct 2026.
  2. peer reviewed paper
    Biochar stability in soil: Meta-analysis of decomposition and priming effects
    Jinyang Wang, Zhengqin Xiong, Yakov Kuzyakov. GCB Bioenergy, Apr 2015. DOI: 10.1111/gcbb.12266. Accessed 21 Oct 2026.
  3. peer reviewed paper
    A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis
    S. Jeffery, F.G.A. Verheijen, M. van der Velde et al.. Agriculture, Ecosystems & Environment, Nov 2011. DOI: 10.1016/j.agee.2011.08.015. Accessed 21 Oct 2026.
  4. peer reviewed paper
    Biochar boosts tropical but not temperate crop yields
    Simon Jeffery, Diego Abalos, Marija Prodana et al.. Environmental Research Letters, 2017. DOI: 10.1088/1748-9326/aa67bd. Accessed 21 Oct 2026.
  5. other
    Biochar Carbon Removal Market Snapshot 2025
    CDR.fyi, 9 Sept 2025. Accessed 21 Oct 2026.
  6. news
    Puro.earth Reaches Major Milestone of 1 Million Tonnes of CO2 Removed
    ESG Today, 20 Mar 2025. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.

Changes on 21 Oct 2026
Published on owner instruction (content loop iteration 9)81096f5
Sources and claims re-checked against originalsfbb434c
Initial profile drafted from primary sources7e66249