Using Biochar Systems to Sequester Carbon
AgMRC Renewable Energy Newsletter
Iowa State University
(second in a series)
Last month we introduced biochar and the multitude of benefits it may provide. This month we will look specifically at the ability of biochar to sequester carbon. In fact, we will examine the entire biochar production system and its ability to sequester carbon through biochar and other methods in the system.
To help understand carbon emissions and carbon sequestration, we divide carbon activities into three types – carbon positive, carbon neutral and carbon negative – as shown below. The advantage of biochar is that it is carbon negative. Essentially, it is a method of reducing atmospheric carbon dioxide by taking atmospheric carbon that is used to build plants and other organic materials and sequestering it in the ground. Biochar has the ability to sequester large quantities of atmospheric carbon.
|Carbon Positive (increases atmospheric carbon)
Takes sequestered carbon and emits it into the atmosphere
(e.g. burning fossil fuels)
Carbon Neutral (no change in atmospheric carbon)
Takes atmospheric carbon and emits it back into the atmosphere
(e.g. natural carbon plant cycle)
Takes sequestered carbon and sequesters it again
(e.g. fossil fuel burning with carbon capture and sequestration)
Carbon Negative (decreases atmospheric carbon)
Takes atmospheric carbon and sequesters it
Cap and trade greenhouse gas legislation currently being debated in the U.S. Congress provides for carbon “offsets”. Essentially this is a process by which “capped” industries (electric utilities, transportation fuel refineries, etc.) can meet their emission reduction requirements by purchasing emission reductions from outside sources. So the implementation of cap and trade legislation would create a large demand for carbon offsets.
Biochar systems have the potential to provide large amounts of high quality carbon offsets that can be purchased by the capped industries to meet their emission reduction requirements. The sale of these offsets can generate an income stream for the producers of the offsets. This sets the stage for the creation of a growth industry which can provide substantial economic benefits not only for U.S agriculture and rural America, but for rural agricultural areas around the world.
An analysis of the potential size of the biochar systems industry was conducted by the International Biochar Initiative. To understand the analysis of these biochar systems for creating carbon offsets, we will examine the processes involved and the basic assumptions underlying the analysis.
Availability of biomass -- Biomass is the feedstock for the biochar systems. So the availability of biomass is critical to the size of the industry. “Primary Production” is the term used to represent the production of organic compounds from atmospheric or aquatic carbon dioxide, principally through the process of photosynthesis. “Net Primary Production” is the difference between the rate at which the plants in an ecosystem produce useful chemical energy and the rate at which they use some of that energy during respiration. The analysis assumes the usage of a portion of the world’s Net Primary Production in the biochar systems.
Estimate of world autotroph biomass
Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE.
Traditionally we have thought of biomass as being essentially a free resource available in unlimited quantities. However, in recent years, concerns about the potential of the world’s agricultural sector to produce sufficient quantities of food for the growing world population and the dangers of diverting a portion of our agricultural production capacity to non-food uses is changing the image of biomass as a free and unlimited resource. So, the analysis includes just biomass residue from crops and forests. For example, if 27 percent of the existing biomass residue from crops and forests is used in a biochar system, it represents only 1.2 percent of the world’s Net Primary Production, as shown in Table 1.
Table 1. Various scenarios of biomass usage for biochar systems.
||Residue from Crops and Forests
||Net Primary Production
As a result, biomass usage scenarios outlined above do not impact the production of food. More aggressive scenarios of biomass usage could involve biomass grown on marginal and degraded lands that may have only a slight impact on agriculture’s food production capacity.
Availability of land for sequestration -- Adequate land area is available for sequestration by returning the biochar to the land from which the biomass was taken. Although the removal of biomass of crop residues from fields can result in the reduction in soil productivity through reduced soil organic matter, returning a portion of the biomass in the form of biochar will more than offset this reduction and actually improve the productivity of the land.
Modern biochar technology -- The analysis assumes that modern high-yielding technology of slow pyrolysis systems is used. The system assumes a 40 percent carbonization rate. In addition to producing biochar, the system produces renewable energy that can be used to substitute for fossil fuel energy and thereby reduce carbon emissions, as discussed in the previous article (link) in this series.
Stability of sequestered biochar carbon -- The value of sequestered carbon is highly dependent on the stability of the sequestration. The danger of a reversal or leakage of the sequestered carbon greatly impacts its value as a viable carbon offset. Biochar has been proven to be a very stable carbon storehouse. Biochar carbon remains sequestered in the soils for hundreds of years or longer.
Carbon sequestration from biochar
Estimates of the amount of carbon sequestered from biochar are presented in Figure 1. The Conservative, Moderate and Optimistic scenarios are based on the amount of biomass used in the biochar systems and is outlined above in Table 1. The term “wedge” represents one billion tons (gigatons) of carbon sequestered per year. As shown in Figure 1, after reaching its full potential, biochar has the ability to sequester from slightly above .2 to almost .8 billion tons of carbon per year. The moderate scenario sequesters about half a billion tons of carbon. The optimistic plus scenario sequesters over a billion tons annually by the year 2050.
Source: International Biochar Initiative
Research indicates that biochar also has the potential to reduce soil emission of nitrous oxide (N2O), an extremely potent greenhouse gas. For example, approximately half of the greenhouse gas emissions from producing corn are nitrous oxide. Also, as shown in the previous article
in this series, applying biochar to soil has the effect of increasing the productivity of the soil.
The Optimistic Plus scenario shown in Figure 1 includes the impact of these two factors. Nitrous oxide emissions are assumed to be reduced by 50 percent and the application of biochar to the soil has the potential to produce 25 percent more biomass due to increased soil productivity from the application of biochar.
Biomass sequestration from biochar and fossil carbon offsets
The biochar systems involve more than just converting biomass to biochar. These systems have the potential to produce significant amounts of bioenergy as discussed in the previous article. The bioenergy is carbon neutral because it emits carbon that was originally atmospheric carbon (converted to plant carbon through photosynthesis). Conversely, fossil fuel (coal) energy is carbon positive because it emits carbon into the atmosphere that was originally sequestered deep in the earth. The bioenergy produced by the biochar systems reduces carbon emissions and generates carbon offsets by substituting carbon neutral bioenergy for carbon positive fossil fuels.
In addition, carbon dioxide emissions generated during the biochar production system can be sequestered through a carbon capture and sequestration process similar to the system being developed for the coal industry.
The impact of the entire biochar system includes:
- the sequestration of carbon through biochar,
- the production of bioenergy and its substitution for fossil fuel (coal) energy
- the capture and sequestration of excess carbon emissions,
The resulting carbon offsets are shown in Figure 2.
Source: International Biochar Initiative
When fully implemented, the reductions range from over one-half billion tons of carbon per year under the conservative scenario to almost two billion tons of carbon under the optimistic scenario. The moderate scenario results in about 1.25 billion tons per year. The optimistic plus scenario increases gradually over time resulting in about 2.20 billion tons by the year 2050.
Impact of biochar systems
To keep GHG levels at the level of 2004, it is estimated that we will need to reduce world greenhouse gas emissions by about seven billion tons per year by the year 2054. Worldwide, biochar systems can make an important contribution to this reduction as shown in Table 2. Biochar alone could contribute about 10 percent of this reduction. When combined with the other offsets, the entire biochar system could contribute about 20 to 30 percent of the reduction.
|Table 2. Estimated potential GHG emission offsets by 2050 from biochar systems under various scenarios.
||Biochar & Fossil Offsets
U.S cap and trade legislation allows capped industries to purchase and utilize both domestic and international carbon offsets. Biochar system can provide a large supply of these carbon offsets. If cap and trade programs are implemented in other nations around the world, the potential demand for carbon offsets from biochar systems could be even larger.
Under three alternative carbon prices, the value of the carbon offsets are shown in Table 3. At a carbon price of $15 per ton, the potential value of the carbon offsets are $18.7 billion dollars under the moderate scenario when the sequestration from both biochar and fossil fuel substitution are included. It increases to $62.5 billion at a carbon price of $50 per ton. The economic impact of these carbon offsets would have a substantial impact on agriculture and rural communities around the world.
|Table 3. Estimated Annual Carbon Offset Values by Scenario under Alternative Carbon Prices (billion dollars).
| Optimistic Plus
|Biochar plus Fossil Offsets
| Optimistic Plus
Research is on-going as to the technology needed for a functioning biochar systems industry and the various types and sizes of production systems needed for diverse feedstock sources and locations around the world.