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 accelerate 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.
“If you could continually turn a lot of organic material into biochar, you could, over time, reverse the history of the last two hundred years…We can, literally, start sucking some of the carbon that our predecessors have poured into the atmosphere down through our weeds and stalks and stick it back in the ground. We can run the movie backward. We can unmine some of the coal, undrill some of the oil. We can take at least pieces of the Earth and – this is something we haven’t done for quite a while – leave them Better Than We Found Them.”
Bill McKibben, author, climate activist and founder of 350.org
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.
Reduced fertilizer inputs: Biochar can reduce the need for chemical fertilizers, resulting in reduced emissions of greenhouse gases from fertilizer manufacture.
2) Reduced N2O and CH4 emissions: Biochar can reduce emissions of nitrous oxide (N2O) and methane (CH4) two potent greenhouse gases from agricultural soils.
3) Enhanced soil microbial life: Biochar can increase soil microbial life, resulting in more carbon storage in soil.
4) 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.
5) 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 green house gasses (GHG) emissions on an annual basis. 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.