Atmosphere And Weather

Removal of Excessive Carbon from the Atmosphere



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How Do We Restore the Balance of CO2?

The jury is out on the removal of CO2 from the atmosphere. It has to go. But at the same time we cannot completely get rid of atmospheric carbon dioxide; there has to be a balance. I can think of two main methods to remove it, with biological or chemical means.

Biological Remediation of Carbon Dioxide
I recently read a letter to the editor of Chemical and Engineering News that echoes my own thoughts. Why can't plants solve the problem? Plants convert CO2 to glucose with the sun's energy via photosynthesis.

carbon dioxide + water + light energy glucose + oxygen + water

Plants have done so until now, but not all of them will be able to process the amount of CO2 thrown at them by us. Increased levels of CO2 affects plants differently. Plants can be classified into C3 and C4 categories based on how they process carbon (and carbon dioxide). Trees are in class C3, and most major crops are C4. C3 plants continue to photosynthesize under very high concentrations of CO2, whereas C4 plants cannot. CO2 will heavily impact plant selection and survival. "Weaker plants" may not survive large amounts of CO2.

I asked colleagues of mine who are plant specialists about photosynthesis. Their response was that when you increase the photosynthesis of a plant (the carbon cycle) you also affect the other nutrients in the soil. Nitrogen (fertilizer) in the soil is depleted and other cycles are affected. These turbocharged plants will require more fertilizer.

Can photosynthesis be made even more efficient through genetic selection or engineering of crops that have high photosynthetic rates? Crops such as rice are already being supercharged to increase production rates by using genetic engineering of key photosynthesis enzymes to boost photosynthesis.

Ironically, plants have already been looked at as a possibility for increased photosynthesis in order to feed our ever expanding world population. At the same time we will need these "superplants" to consume more CO2 to assist in keeping the carbon cycle in balance. Only time will tell if we can succeed in engineering the enzymes and plants to do this.

Chemical Uses of Carbon Dioxide

In addition to biological means of processing CO2 there are chemical ways. Carbon sequestration, or burying carbon under ground is one way. However there are many chemical reactions that require carbon dioxide. The use of supercritical carbon dioxide is one.

Supercritical carbon dioxide is a physical state where it has behavior that is in between being a liquid and a gas. This happens under extremely high pressure (liquid-like) and temperature (gas-like). Decaffeination of coffee is achieved through the use of supercritical fluids.

Two examples of specific reactions were given in the November 19, 2007 issue of Chemical and Engineering News. One example was the use of supercritical CO2 and a metal catalyst in converting biomass feedstock to a renewable transportation fuel or chemical starting material. The other was a similar reaction that ads on a carbon and an oxygen in a chemical synthesis using supercritical CO2 and similar catalyst.

In the end, we have important knowledge at our disposal about the biology and chemistry behind removing carbon dioxide. It seems we need to use other forces, our ingenuity, international cooperation and financial backing to solve the problem.

References:

http://www.serc.si.edu/labs/co2/c3_c4_plants.jsp
http://www.marietta.edu/~biol/102/ecosystem.html
http://www.sciencemag.org/cgi/content/summary/313/57 86/423a
http://www.sciencemag.org/cgi/content/summary/283/54 00/314
http://www.cababstractsplus.org/google/abstract.asp? AcNo=20043032349
http://www.cababstractsplus.org/google/abstract.asp? AcNo=20043109521
http://www.economist.com/science/displaystory.cfm?st ory_id=8380318
http://www.gcrio.org/gccd/gcc-digest/1993/d93feb6.ht m

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