Biochar: A critical perspective

New Biofuelwatch briefing, May 2024: What does the science tell us about whether biochar reliably stores carbon and boosts soil fertility?


In 2011, Biofuelwatch published a comprehensive report, “Biochar: a critical review of science and policy”. In 2020, we provided an update to that report. Given the proliferation of initiatives to develop commercial-scale biochar and burgeoning policy and financial support, we feel compelled to provide this more recent update.

The published literature has dramatically expanded, reflecting great interest and an influx of funding to soil science research. Additionally, there has in recent years been a widening of the scope of proclaimed ‘uses’ for biochar – no longer just for carbon  sequestration or soil and crop improvement, but also for remediation of toxins, as a feed supplement for livestock to reduce methane emissions, for treatment of
waste water and more.

The overarching problem remain as results from biochar studies continue to be highly inconsistent, depending on what feedstock is used, how it is produced, the type of soil to which it is applied, the environmental conditions, what crop is grown, the study duration, and what kinds of measurements are made. Understanding of biochar is far from what would be required to enable reliable control over its influence on the environment. Given the risks discussed further below, it is highly premature to
promote biochar as deserving subsidies and other incentives.

Yet those policy support measures for biochar as a ‘carbon negative technology’ are being put in place. We are not alone in urging precaution, many in the scientific research community express similar reservations. For example: in “Rethinking biochar: black gold or not?” (Tan et al 2023) the authors conclude: “To date there is no conclusive evidence demonstrating environmental friendliness or long-term cost effectiveness of large scale biochar implementation in soil and climate agro-economic systems, let alone in water purification and energy storage and conversion.”

Xiang et al (2021) warn: “Considering the harmful components, structure and particle size of biochar, the negative effects of biochar application on the environment should not be ignored.