Stages of Coal Formation

Understanding the different types of coal involves first developing a basic understanding of how coal forms within the earth. The types of coal are differentiated by specific properties which result from having undergone varying degrees of heat and pressure over different lengths of time during formation. Coal takes millions of years to develop, and is derived from ancient plant matter that has been subjected to intense heat and pressure that affected physical and chemical alterations. The process through which coal forms from such ancient plants is known as coalification.

In general, coal forms from the remains of plants which died in prehistoric swamps and wetlands. Organic plant matter at various stages of decay form peat, which, under certain pressure, time and heat conditions experiences slow rates of bacterial decay and eventually goes on to form coal. As peat is buried by sediment and becomes compressed, it slowly releases water and other elements contained within it, resulting in an increasingly compact and carbon rich substance. The natural process converting plant matter to peat may go through different stages, first forming lignite, then sub bituminous coal, bituminous coal and eventually anthracite coal.

When we mine coal from the earth, it may be at any of the above mentioned stages of formation, which contain increasing levels of carbon. Below we examine some of the characteristics of each rank:

-Lignite: Lignite coal is the lowest ranked coal for its heat energy producing capability and carbon content. A soft, brownish coal, lignite contains the highest levels of moisture of the coal types and is known for its crumbly texture. Lignite deposits are the youngest of the coal types and have undergone the lowest intensity of heat and pressure.

-Sub Bituminous: With higher carbon content and thus a higher heating value than lignite, sub bituminous and bituminous coal collectively make up the majority of coal produced in the United States. Sub bituminous coal contains less water and is therefore harder than lignite, facilitating easier transportation and storage. The relatively low sulfur content in sub bituminous coal makes it an attractive option for power plants.

-Bituminous: Estimated to be between 100 and 300 million years old, bituminous coal makes up the majority of coal mined in the U.S. Bituminous coal is heavily utilized for energy in power plants and for the production of steel.

-Anthracite: Having the highest concentration of carbon, anthracite is also the hardest coal. Anthracite coal is known to be the cleanest burning coal, but is one of the rarest, being found mainly in limited reserves in Pennsylvania.

Farming Carbon

The House Committee on Natural Resources recently held a hearing on geological and terrestrial sequestration of carbon dioxide. The House Committee on Energy and Commerce held a similar hearing in March.

Congress' new enthusiasm for technological climate change solutions has spread across both parties and throughout the Washington DC. On Tuesday, May 1 Senator Saxby Chambliss issued a press release on his hopes for voluntary carbon offset trading as a supplement to farm income.

Currently, farmers who wish to profit from the sequestration potential of their soils can sell carbon credits on the Chicago Climate Exchange (CCX). The exchange offers binding contracts to companies and cooperatives that wish to voluntarily offset their emissions. The CCX does not certify individual farms for sequestration. Instead, it relies on third-parties called aggregators who compile databases of farmers willing to adopt carbon-friendly management practices. From those databases, CCX randomly selects farms for field visits. Once an aggregator’s sample farms are certified its entire portfolio is ready for trading.

After an aggregator trades its portfolio, individual farmers receive their allotted share of the sale less a 10 percent administrative fee for the aggregator. There are only two aggregators presently working to certify conservation-minded farmers - the National Farmers Union’s Carbon Credit Program and the Iowa Farm Bureau Carbon Credit Aggregation Program.

Under both NFU and Iowa Farm Bureau aggregation plans all producers willing to adopt conservation tillage best practices are credited with 0.5 metric ton of carbon for each acre of eligible no-till cropping and 0.75 ton per acre for qualifying grass stands each year of the contract.

To be eligible, lands must be classified as "crop land" by the USDA's Farm Service Agency. Producers must also agree to use conservation tillage as defined in the Natural Resources Conservation Service National Handbook of Conservation Practices.

According to the Iowa Farm Bureau these definitions are: No-till/Strip-till - Managing the amount, orientation, and distribution of crop and other plant residue on the surface year-round while growing crops in narrow slots or tilled or residue-free strips in soil previously untilled by full width inversion implements.

Fallow: In areas where non-tillage fallow is an acceptable practice, no credits shall be issued for the year in which the land is fallowed.

Crop Residue Removal: No credits shall be issued on otherwise eligible cropland (row crops and small grains) during any year in which crop residue is removed by harvest or burning. Crop harvest is permitted for alfalfa and grass hay and through grazing of grass.

As the programs have expanded, aggregators have placed additional regional requirements on sequestering farmers. The Iowa Farm Bureau's requirements are available here.

Since 2003, CCX carbon prices have hovered around $4 per ton of sequestered carbon. Assuming a price of $4 per ton, participating farmers will receive $2.00 per acre for no-till and $3.00 per acre for grass stands, minus the aggregation fee.

At present, aggregators don't attempt to gauge the carbon impact of individual farms nor do they quantify counterbalancing emissions of traces gases. Hopefully, ASA/CSSA/SSSA members can play a constructive role in the CCX, providing the scientific basis on which aggregators will improve their climate accounting.