Senebier's carbon cycle in its original and simplest form, described the absorption of atmospheric carbon dioxide by plants, which are subsequently eaten by animals, who in turn return the carbon dioxide to the atmosphere by respiration and
Table 3.5 Global carbon budget.
Fossil fuel combustion Tropical deforestation
Retained in atmosphere Ocean uptake
Uptake by Northern Hemisphere reforestation
excrement. This concept and a more extended form of the carbon cycle, including fossil fuel usage, is shown in Fig. 3.4. Carbon-rich fossil fuels, oil, coal and natural gas, are extracted from the near surface of the earth and burned as energy sources. The combustion of fossil fuels produces large quantities of carbon dioxide, oxides of nitrogen and sulfur together with soot. Since the Industrial Revolution the proportion of these gases in the atmosphere has increased, accompanied by a corresponding rise in the global average near surface temperature; the greenhouse effect.1 Typical carbon fluxes associated with the major components of the cycle are shown in Table 3.5. The only significant natural absorption mechanism for excess carbon dioxide is via vegetation and this is not able to keep pace with the rate of fossil fuel-generated emissions. Equally serious are the geological timescales needed for the plant life cycle to replace the original coal or oil resources. Thus, whilst similar in mechanisms, the traditional carbon cycle and the fossil fuel cycle, shown on opposite sides of Fig. 3.4, differ in cycle times by tens of thousands of years. This fundamental imbalance has a number of major consequences, the most important being:
1. Use of fossil fuels, particular petrol chemicals, is rapidly depleting a finite and nonrenewable resource.
2. Carbon dioxide emissions from fossil fuel combustion will accumulate and accelerate the greenhouse warming mechanisms underlying global warming.
To escape from these impending crises, a fuel system capable of providing ongoing energy sources in a nonpolluting manner is needed. Fortunately, the hydrogen cycle, which has a similar timescale to that of the carbon bio-system, can provide an answer.
1 Solar heating of the Earth occurs via shortwave radiation, which is absorbed by the Earth's surface and then reflected back as longer wavelength radiation. A fraction of the long wavelength radiation can be trapped by "greenhouse gases" in the upper atmosphere, thus creating a blanket effect and raising global temperatures .
Was this article helpful?
Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.