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, reradiates much of the received energy as long-wavelength radiation, which carbon dioxide absorbs and then remits toward 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 effect is shown by Venus, a planet covered by heavy clouds composed mostly of carbon dioxide, whose surface temperatures have been measured at 43012. If the carbon dioxide content of the atmosphere is reduced, the temperature falls. 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 a halving of the carbon dioxide concentration would lead only to reduction in global temperatures of 312.
If, because of an increase in forest fires or volcanic activity, the carbon dioxide content of the atmosphere increased, 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, in turn, would 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 at least 1℃. But a supposed global temperature rise of 112 may in reality be only several regional temperature increases, restricted to areas where there are many meteorological stations and mused 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.
Which of the following questions does the passage supply information for answering？

A. Why are projections of the effects of changes in water vapor levels oh the climate so inaccurate？
B. What are the steps in the process that takes place as carbon dioxide absorbs long-wave length radiation？
C. How might our understanding of the greenhouse effect be improved if the burning of fossil fuels were decreased？
D. What might cause a series of regular increases and decreases in the amount of carbon dioxide in the atmosphere？