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Climate Change and Biochar

How Can Biochar Be Carbon Negative?

Fossil fuels are carbon positive; they add more carbon dioxide (CO2) and other greenhouse gasses to the air and thus exacerbate global warming. Ordinary biomass fuels are carbon neutral; the carbon captured in the biomass by photosynthesis would have eventually returned to the atmosphere through natural processes like decomposition. Sustainable biochar systems can be carbon negative by transforming the carbon in biomass into stable carbon structures in biochar which can remain sequestered in soils for hundreds and even thousands of years. The result is a net reduction of CO2 in the atmosphere, as illustrated in the diagram.

Diagram courtesy of Nature Publishing Group

Climate Smart Benefits of Biochar

Carbon in biochar can persist in soils over long time scales. Beyond the carbon sequestered in the biochar itself, biochar incorporated in soils also offers numerous other potential climate benefits.

  1. Soil Fertility: Biochar can improve soil fertility, stimulating plant growth, which then consumes more CO2 in a positive feedback effect.
  2. Reduced fertilizer inputs: Biochar can reduce the need for chemical fertilizers, resulting in reduced emissions of greenhouse gases from fertilizer manufacture.
  3. Reduced N2O and CH4 emissions: Biochar can reduce emissions of nitrous oxide (N2O) and methane (CH4)—two potent greenhouse gases—from agricultural soils.
  4. Enhanced soil microbial life: Biochar can increase soil microbial life, resulting in more carbon storage in soil.
  5. Reduced emissions from feedstocks: Converting agricultural and forestry waste into biochar can avoid CO2 and CH4 emissions otherwise generated by the natural decomposition or burning of the waste.
  6. Energy generation: The heat energy—and also the bio-oils and synthesis gases—generated during biochar production can be used to displace carbon positive energy from fossil fuels.

How Much Carbon Can Biochar Remove from the Atmosphere?

According to one prominent study (Woolf et al, 2010), sustainable biochar implementation could offset a maximum of 12% of anthropogenic GHG emissions on an annual basis. Over the course of 100 years, this amounts to a total of roughly 130 petagrams of CO2-equivalents. The study assessed the maximum sustainable technical potential utilizing globally available biomass from agriculture and forestry. The study assumed no land clearance or conversion from food to biomass-crops (though some dedicated biomass-crop production on degraded, abandoned agricultural soils was included), no utilization of industrially treated waste biomass, and biomass extraction rates that would not result in soil erosion.

The figure to the right (from Woolf et al, 2010) shows avoided emissions attributable to sustainable biochar production or biomass combustion over 100 years, relative to the current use of biomass. Three scenarios are modelled showing different degrees of demands on global biomass resources (red=maximum sustainable technical potential (MSTP); blue=medium; black=low). Sustainable biochar is represented by solid lines; biomass combustion by dashed lines. The top panel shows annual avoided emissions; the bottom panel, cumulative avoided emissions over 100 years. In all three scenarios sustainable biochar trumps biomass combustion in terms of avoided emissions.

For further information on biochar and climate change, please review the Frequently Asked Questions on biochar.

Diagram courtesy of Nature Publishing Group

Biochar in Carbon Trading Markets

One of the most critical characteristics of biochar as a climate change mitigation technology is its long-term persistence in soil. Quantification of the persistent carbon component of biochar can facilitate the participation of biochar projects in carbon markets, providing an additional revenue stream to projects delivering greenhouse gas emissions reductions through soil carbon sequestration.

Several attempts have been made to create biochar carbon offset methodologies in existing voluntary carbon market registries but to date none have been approved for use. Most prominently, IBI along with partners The Climate Trust and The Prasino Group, submitted a proposed biochar carbon offset methodology to the American Carbon Registry (ACR)—a leading voluntary carbon offset registry. In March 2015, after three years of review, this draft methodology was listed as inactive by ACR due to concerns around the embedded test method to estimate biochar carbon persistence (known as BC+100)—used to estimate the quantity of biochar carbon remaining in the soil after 100 years. Future efforts to revive the methodology in the ACR process—and indeed other carbon offset registries—should focus on bolstering the evidence for BC+100, or identifying novel methods to measure, monitor and verify biochar carbon persistence under field conditions.

For further information on the ACR Biochar Carbon Offset Methodology, including a draft of the metholody and the test proceedure, see: