CARBON dioxide has a major image problem. This most benign of substances has been pilloried in recent years as one of the great evils of our time - a foul pollutant, a 20th century aberration, an environmental vandal of which the world would be well rid. But nothing could be further from the truth. CO2 is an essential ingredient of our atmosphere: among other things, it plays an important part in regulating, the temperature of our planet, and without it life on Earth could not exist at all.
In fact there is only a tiny amount of carbon dioxide in "the atmosphere, comprising, about 0.035 per cent of its total volume. Its presence can be traced to infusions of carbon, largely due to the burning of fossil fuels - oil, natural gas, or coal - that have been mined or piped from the bowels of the earth. The burning of one ton of carbon, say in the form of coal, produces four tons of carbon dioxide, as each atom of carbon combines with two of oxygen to give the familiar formula CO2,
It is interesting however, to trace the history of this carbon. Evelyn Waugh, describing the golden years of youthful batchelorhood in Vile Bodies, remarks that "we emerge for a short while into the sunlight, and then the front door closes behind us". Atmospheric carbon has, in cosmic terms, a moment of freedom that is similarly brief. Much of it is re absorbed by plants through the process of photosynthesis, or captured by the micro organisms of the world's oceans.
We humans and other animals sometimes eat these plants, and expel carbon dioxide once again into the atmosphere by the exercise of breathing. Sooner or later, however, if nature is allowed to take its course, the carbon is re absorbed into the substance of the planet: most of the world's carbon lies embedded in the sedimentary layers, deep beneath the oceans and the surface of the earth, and there it may form the basis for the fossil fuels of the very distant future, ultimately perhaps to re emerge in the atmosphere completing what is called the "carbon cycle".
We are told that the average carbon atom released into the atmosphere during the combustion of fossil fuel will flit back and forth between plants, soil, air and water for approximately 100,000 years before eventually returning to the quiescent reservoir of the sediments. And this same average atom has made the complete cycle from the sediments through the various possible paths in the carbon cycle and back to sediment again some 20 times over the four billion years of the earth's history.