The greenhouse effect is an issue that concerns all of us. Climate conditions are delicately adjusted to the composition of the Earth’s atmosphere. If there were a change in the atmosphere, for example, in the relative proportion of atmospheric gases, the climate would probably change also. A slight increase in water vapor, for instance, would increase the heat-retaining capacity of the atmosphere and would lead to a rise in global temperatures. In contrast, a large increase in water vapor would increase the thickness and extent of the cloud layer, reducing the amount of solar energy reaching the Earth’s surface.
The level of carbon dioxide in the atmosphere has an important effect on climatic change. Most of the Earth’s incoming energy is short-wavelength radiation, which tends to pass through atmospheric carbon dioxide easily. The Earth, however, re-radiates much of the received energy as long-wavelength radiation, which carbon dioxide absorbs and then remits towards the Earth. This phenomenon, known as the greenhouse effect, can result in an increase in the surface temperature of a planet. An extreme example of the greenhouse effect is shown by Venus, a plant covered by heavy clouds composed mostly of carbon dioxide, whose surface temperatures have been measured at 430℃. If the carbon dioxide content of the atmosphere is reduced, the temperatures fall. According to one respectable theory, if the atmospheric carbon dioxide concentration were halved, the Earth would become completely covered with ice. Another equally respectable theory, however, states that halving the carbon dioxide concentration would lead only to a reduction in global temperature of 3℃.
If, because of an increase in forest fires or volcanic activity, the carbon dioxide content of the atmosphere increase, a warmer climate would be produced. Plant growth, which relies on both the warmth and the availability of carbon dioxide, would probably increase. As a consequence, plants would use more and more carbon dioxide. Eventually, carbon dioxide levels would diminish and the climate would in turn become cooler. With reduced temperatures many plants would die; carbon dioxide would thereby be returned to the atmosphere and gradually the temperature would rise again. Thus if this process occurred, there might be a long-term oscillation in the amount of carbon dioxide present in the atmosphere, with regular temperature increases and decreases of a set magnitude.
Some climatologists argue that the burning of fossil fuels has raised the level of carbon dioxide in the atmosphere and has caused a global temperature increase of 1℃. But a supposed global temperature rise of 1℃ may, in reality, be only several regional temperature increases, restricted to areas where there are many meteorological stations and caused simply by shifts in the pattern of atmospheric circulation. Other areas, for example, the southern Hemisphere Oceanic Zone, may be experiencing an equivalent temperature decrease that is unrecognized because of the shortage of meteorological recording stations.