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Permanent Wood Sequestration as a Means to Solve the Global CO2 Problem
28 May, 2008 11:57 am
By Drs. Fritz Scholz and Ulrich Hasse: The increasing carbon dioxide (CO2) concentration in the atmosphere ranks first among the global environmental threads because it causes a constantly growing average temperature (anthropogenic greenhouse effect).
The reason for the increasing carbon dioxide concentrations is the use of fossil fuels for energy production and motor fuel in cars and airplanes. The biosphere of the world annually binds 550-600 Gt of CO2, and the same amount is released from the biosphere by oxidative decomposition and degradation of biomass. This situation led to a rather stable CO2 concentration over the last millions of years.
The human race has changed that delicate equilibrium by using fossil carbon sources like coal, natural oil and gas, carbon sources that have been build in geological time spans, millions of years before now. The burning of these fossil fuels leads to an annual input of 32 Gt CO2. Luckily, only roughly one half of that CO2 stays in the atmosphere because there are some buffers, e.g., the ocean waters that are still able to absorb CO2, although not without negative side effects (esp. acidification of the oceans).
The best strategy to reduce the CO2 input is, without any question, to abandon the use of fossil fuels and to produce energy with the help of so called regenerative energy sources, as wind, sun, water, geothermal energy. However, a realistic view on current developments quickly reveals that this substitution is a very slow process, and we are still seeing an unprecedented growth of oil, gas, and coal production due to the growing demand in the industrialized as well as in the developing countries.
Hence, it is not pessimism, but simple realism if one concludes that the use of fossil fuels will accompany us also in the next decades, at least. Therefore, we are facing the pressing question: How can we reduce the CO2 content of the atmosphere despite the ongoing input? That can be only achieved by a process that fulfils two requirements: (i) it must be capable of binding Giga tons of CO2, and, (ii) it must bind the CO2 permanently, i.e., we have to be sure that the CO2 will not be released back to the atmosphere.
To the best of our knowledge, these two requirements can only be met by the process of wood growth, and a subsequent sequestration of the wood under anaerobic conditions. The wood growth can be rather easily accomplished by forestation of fallow land, and the anaerobic sequestration can also be rather easily performed by burying the wood in open pits of brown coal mines or any other mines. When the wood is covered under 50, 100 or more meters of soil, it will keep practically for infinite times, with only some minor carbonization, i.e., without any loss of carbon.
Since wood contains ?reduced carbon dioxide?, it happens that 1 ton of wood is equal to 1.8 t of CO2. In a recently published essay (1), we propose that wood-growth-and-burial process as a realistic way to solve the carbon dioxide problem. We show that this process allows to get rid of the CO2 in a most cost-efficiency way: To sequester 1 t CO2 it would need in Europe about 50 ?, and it is easy to understand that this price may be substantially lower in other regions of the world. That price needs to be compared with the price for pressing CO2 in emptied cavities of natural gas: that will cost between 500 and 600 ? per t of CO2, and it needs to be said that this so-called CO2-sequestration is a process with still unknown but expected risks, and it is known that the CO2 will most probably slowly escape back to the atmosphere.
From environmental point of view that CO2-sequestration cannot be the solution. On the other side, the wood-growth-and-burial process can be performed in such way that it will have only positive environmental effects: (i) permanent removal of CO2 from atmosphere, (ii) forestation of abandoned land (fallow land), (iii) positive climate effects due to water circulation, (iv) improving air quality, (v) biotope conservation, etc. Not at least, the wood-growth-and-burial process can create jobs especially in the developing countries.
Literature for further reading:
(1) F. Scholz, U. Hasse: ChemSusChem 1 (2008), 381.
(2) J. C. Zachos, G. R. Dickens, R. E. Zeebe, Nature 2008, 451, 279-283.
(3) S. A. Zimov, E. A. G. Schuur, F. S. Chapin III, Science 2006, 312, 1612-1613.
(4) A. C. Revkin, A ?bold? step to capture an elusive gas falters. The New York Times, February 3rd, 2008
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To reduce the amount of this that is needed, would it not be better to partially gasify the wood to produce a flammable gas, forming char in the process, and then burying the char to increase carbon content of the soil, while the flammable gas is burned for energy needs?