By Dominic Pietro
Forests have limited use for carbon sequestration. Most of their carbon storage occurs in the wood itself, so a mature forest has a very slow rate of carbon sequestration; most happens while the trees are still growing. Most technological solutions CO2 removal and sequestration are still a long way from being fully developed and are expensive. At least one man has developed a method to turn CO2 into graphite, a highly stable form of carbon. The possibility of combining this new process with afforestation could lead to slow, but cheap and long-term or permanent carbon storage.
Carbon sequestration is likely to be an important part of the solution to global warming caused by anthropogenic greenhouse gas release, along with greatly reducing the amount of greenhouse gases that we emit into the atmosphere. Carbon sequestration is any method by which carbon is stored in some form so as to keep it out of the atmosphere. Before carbon can be sequestered, however, it must be captured and removed from the atmosphere (in the form of carbon dioxide, CO2), or else it will do nothing to fight global warming.
Nature has already provided a very common method of carbon capture – photosynthesis. Plants take in CO2 from the atmosphere, extract the carbon and use the element as part of their physical structure. Besides being stored in living plants, plant residue stores some carbon, and while much carbon will be released during decomposition, some carbon end up in the soil. Any vegetated area will store some amount of carbon in the plants and in the soil, but it varies greatly by type of plant and region. Trees store a tremendous amount of carbon in their woody parts, and cold, dry climates store the most carbon in their soils, as conditions slow decomposition.
Under the Chicago Climate Exchange (CCX), a voluntary carbon trading system, owners of plots of land can institute certain land-use practices in order to store carbon, and this stored carbon is worth credits that can be sold on the exchange to parties wishing to offset their own carbon emissions (“Chicago Climate Exchange,” n.d.). Reforesting a plot of land that has not been forest since before a certain baseline date, or afforesting an area that has never been forest, are the two practices that store the most carbon and therefore are worth the most credits.
There is a problem with this approach, and it has to do with the nature of trees and forests. While a forest has a great deal of average carbon storage over time, once a forest matures, its rate of carbon storage slows a great deal or stops. The forest is still storing a lot of carbon, but is not removing any new carbon from the atmosphere, on average.
Technological means of carbon capture are being developed and tested as well, though none have yet been proven technologically or economically feasible. Some remove ambient CO2 directly from the air, others are meant to remove CO2 from the smokestacks of fossil fuel burning power plants. The latter would not decrease the amount of CO2 in the air, but rather prevents more from being emitted.
A recent article discusses a recently invented form of carbon capture, called Cozenage Capture (“Turning Emissions Into Diamonds,” n.d.). It has been developed by a man in Australia, and while it is somewhat secretive and details are sparse, it supposedly will capture the CO2 emitted from a coal-burning power plant, and using a bit of steam, will convert the carbon in the CO2 into graphite. According to the article, a prototype plant should go online in mid 2010, and whether it works and is economical should become apparent then.
Graphite is a very stable form of carbon (“Graphite – Wikipedia, the free encyclopedia,” n.d.), and is also a valuable commodity. The graphite formed by the Cozenage Capture process could be sold on the market, and unless the graphite is burned, the carbon should remain out of the atmosphere for a very long time.
Under certain carbon trading schemes, carbon credits can also be issued when timber is used to build long lived object, thereby putting the carbon into long-term storage. Since these credits are worth money, the Cozenage graphite may be more valuable if sold to manufacturers who use it to create long-lived products, such as steel, creating an incentive to use the graphite in a way that better reduces global warming.
Though details are sketchy about the Cozenage Capture process, it seems likely that it could be used to capture the carbon from the burning of other materials besides coal; it seems that steam is the main ingredient in the process, and virtually anything can be burned to produce steam.
This brings me back to afforestation as a means of carbon capture. It seems very possible that the Cozenage Capture process could be adapted to capture the CO2 emitted from burning wood. This may lead to a way to conveniently and economically remove carbon from the atmosphere and to also sequester it in a long term manner.
The idea would be this: find abandoned cropland, marginal land, or some other place where re/afforestation makes sense. Grow an artificial forest of a fast growing variety of tree, such as fast growing hybrid poplars. Growing the trees will remove carbon from the atmosphere and store it in the wood of the trees.
Once the stand of trees is mature, begin a rotating harvest/ replanting schedule. This would mean that the oldest part of the stand would be cut down, and in its place, new trees would be planted. Then, the next oldest part would undergo the same treatment. The timing would be such that, as the last part of the stand is cut, the first part to be cut down and replanted will now have reached maturity, and can once again be harvested and replanted. Carbon credits would be obtained for the duration of time that the trees were growing.
The second part of this potential carbon sequestration method would then involve burning the harvested wood. Using the Cozenage Capture process, the CO2 released in the burning (which is approximately equivalent to the CO2 stored over the lifetime of the tree) would have its carbon removed and transformed into graphite. The graphite is then sold to be an ingredient in a long-lived product.
This allows carbon capture from the atmosphere to be permanent, on-going process. The forest will never reach a point where no new carbon is stored, because as the trees approach maximum carbon storage capacity, the carbon is made into graphite, which can potentially be considered permanent storage, while newly planted trees continue to act as carbon sponges.
For carbon storage that could potentially be indefinite, the graphite could simply be buried in the ground, where it could remain for thousands or millions of years. Graphite is, in essence, “pure” coal, and coal seams have stored carbon deep underground for millions of year prior to our unearthing of it.
However, this seems unlikely, as the market price of graphite ranges from 150 to over 3,000 USD per ton(“USGS Graphite Mineral Commodity Summary 2009,” n.d.), whereas the current price per ton of carbon in carbon trading schemes is around $1.50(“Chicago Climate Exchange,” n.d.). Even if the price of carbon credits gets much higher, as it may in coming years, it has an incredibly long way to go before it even approaches the price of graphite. What may be more likely is that, if enough graphite was being produced by the Cozenage Capture process, either by burning trees or coal, and the graphite supply outpaced demand, then it may become worth it to sell the excess graphite simply as carbon credits and bury the material in the ground.
The combination of growing trees/converting them to graphite would be a fairly slow method of carbon sequestration, but trees are known to capture carbon, whereas we still have a long ways to go to perfect artificial forms of carbon capture. Unless of course the Cozenage Capture process works. And this entire hypothetical sequestration method would hinge on this or another capture process working, and that remains to be seen.
Chicago Climate Exchange. (n.d.). . Retrieved April 21, 2009, from http://www.chicagoclimatex.com/.
Graphite – Wikipedia, the free encyclopedia. (n.d.). . Retrieved April 21, 2009, from http://en.wikipedia.org/wiki/Graphite.
Turning Emissions Into Diamonds. (n.d.). . Retrieved April 21, 2009, from http://money.ninemsn.com.au/article.aspx?id=796109.
USGS Graphite Mineral Commodity Summary 2009. (n.d.). . Retrieved April 21, 2009, from http://minerals.usgs.gov/minerals/pubs/commodity/graphite/mcs-2009-graph.pdf.