The Carbon Dioxide Cycle

The total quantity of carbon on Earth is about 41,000 billion metric tons (92% in the oceans, 6% on land, and 2% in the atmosphere). Prior to the Industrial Age, the concentration of C02 in the atmosphere was stable and balanced. Two hundred and ten billion tons of carbon dioxide entered the atmosphere and approximately the same amount was taken from the atmosphere by the photosynthesis of plants. That balance has been upset by fuel combustion, deforestation, and changing land use as the population increased. 

Post-Oil Energy Technology After the Age of Fossil Fuels 

Carbon Flux Indicated by Arrows Natural Flux = 

Global carbon cycle in billion metric tons of carbon per year. (From Intergovernmental Panel on Climate Change, 2001, U.S. Energy Information Administration.) 

World C02 emissions are expected to increase by 1.9% annually from 2001 to 2025. Much of the increase in these emissions is expected to occur in the developing world, where emerging economies such as China and India fuel their economic development mostly with fossil energy. China s C02 emissions in 2007 exceeded those of the United States, and emissions of the developing countries are expected to surpass those of the industrialized countries about the year 2018. In terms of per capita carbon dioxide emissions, the United States is still the leader with a 21 tons/per capita/per year emission (Russia 11.8, EU 8.6, China 5.1, India 1.8), and these emissions continued to increase in all parts of the world except the EU, where it has been reduced by 2%. 

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Fig. 11-18 A four-box model of the global carbon cycle. Reservoir inventories are given in moles and fluxes in mol/yr. The turnover time of CO2 in each reservoir with respect to the outgoing flux is shown in brackets. (Reprinted with permission from L. Machta, The role of the oceans and biosphere in the carbon dioxide cycle, in D. Dryssen and D. Jagner (1972). "The Changing Chemistry of the Oceans," pp. 121-146, John Wiley.)...

Keeling, C. D. (1973a). The carbon dioxide cycle. Reservoir models to depict the exchange of atmospheric carbon dioxide with the oceans and land plants. In "Chemistry of the Lower Atmosphere" (S. Rasool, ed.), pp. 251-329. Plenum Press, New York. 

Machta, L. (1972). The role of the oceans and biosphere in the carbon dioxide cycle. In "The Chang-... 

Revelle, R. and Munk, W. (1977). The carbon dioxide cycle and the biosphere. In "Energy and Climate," pp. 140-158. National Academy of Sciences, Washington, DC. 

Dmffel E. R. M. (1985) Detection of El Nino and decade timescale variations of sea surface temperature from banded coral records implications for the carbon dioxide cycle. In The Carbon Cycle and Atmospheric CO2 Natural Variations Archean to Present. American Geophysical Union, Washington, DC, pp. 111-122. 

The balance between animal and plant life cycles as affected by the solubiHty of carbon dioxide ia the earth s water results ia the carbon dioxide content ia the atmosphere of about 0.03 vol %. However, carbon dioxide content of the atmosphere seems to be increa sing as iacreased amounts of fossil fuels are burned. There is some evidence that the rate of release of carbon dioxide to the atmosphere may be greater than the earth s abiHty to assimilate it. Measurements from the U.S. Water Bureau show an iacrease of 1.36% ia the CO2 content of the atmosphere ia a five-year period and predictions iadicate that by the year 2000 the content may have iacreased by 25% (see Airpollution). 

We consider first Cycles A of Table 8.1 A and the a.ssociated Figs. 8.6-8.8. These are cycles in which the major objective is to separate or sequestrate some or all of the carbon dioxide produced, and to store or dispose it. This can be achieved either by direct removal of the CO2 from the combustion ga.ses with little or no modification to the existing plant or by modest restructuring or alteration of the conventional power cycle so that the carbon dioxide can be removed more easily. 

Clearly, the carbon dioxide tax will be a dominant factor in future economic analyses of novel cycles. It would appear that a tax of about 3 c/kg of CO2 produced would make some of the CO2 removal cycles economic when compared to the standard basic cycles. 

Shikazono, N. and Kashiwagi, H. (1999) Carbon dioxide flux due to hydrothermal venting from back-arc basin and island arc and its influence on the global carbon dioxide cycle. 9th Annual V.M. Goldschmidt Conference, August 22-27, Harvard University, Abst., p. 272. 

The carbon dioxide molecules including a radiocarbon atom are chemically undistinguishable from those of ordinary carbon dioxide, with which it mixes, and eventually, carbon dioxide, including a radiocarbon atom, is homogeneously distributed throughout the earth s atmosphere and hydrosphere. Thus there is a state of constant production, distribution, and decay of radiocarbon, which results in the relative amount of radiocarbon in the atmosphere and hydrosphere remaining constant. In this homogeneously distributed condition, radiocarbon enters the carbon cycle - as the... 

A numerical example of the carbon dioxide supercritical cycle has been made by Feher (Feher, E.G., The super-critical thermodynamic power cycle. Energy Conversion, vol. 8, pp. 85-90, 1968). The reasons for the neglect of the supercritical cycle until now are not known. 

Weathering is the process by which rock is broken down into smaller and smaller particles. It involves both mechanical and chemical breakdowns. The mechanical breakdown into smaller and smaller pieces occurs as a result of exposure to freeze-thaw cycles and to the action of wind and water. Chemical breakdown occurs as a result of exposure to air and water and other chemicals that may be dissolved in water, such as acids. Weathering by exposure to atmosphere results in some of the carbon dioxide being removed from the atmosphere along with the broken-down rock and eventually washed into the ocean. 

It may be protested that the reaction of the citric acid cycle by which oxaloacetate is converted to oxo-glutarate does not follow exactly the pattern of Fig. 17-18. The carbon dioxide removed in the decarboxylation step does not come from the part of the molecule donated by the acetyl group but from that formed from oxaloacetate. However, the end result is the same. Furthermore, there are two known citrate-forming enzymes with different stereospecificities (Chapter 13), one of which leads to a biosynthetic pathway strictly according to the sequence of Fig. 17-18. 

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