Question

Explain the theory that lies behind global warming.

Answer 1

Generally, the earth’s atmosphere reflects about 30% of the electromagnetic (radiant) energy that comes from the sun. The remaining 45% reaches the surface. As the surface warms up, it radiates more energy back to the atmosphere (some of which is absorbed), and then to outer space. The warmed atmosphere radiates some of its energy into outer space, and some towards the earth’s surface. Glass, which is used to make a greenhouse (for growing plants, especially in winter), is transparent to visible light but opaque to most infrared wavelengths. Similarly, each gas in the atmosphere has its own absorption spectrum— denoting the wavelengths it absorbs and those it transmits. The infrared waves emitted by the earth constitute the heat radiation. Some gases in the earth’s atmosphere are strong absorbers in the infrared range. These gases absorb radiation emitted by the warmed surfaces of the earth. Once warmed, the gases re-emit this radiation. In trapping the heat this way, these gases act similar to the glass in a greenhouse (although the process by which the heat is trapped is not the same as in a greenhouse). Hence, the effect is called the greenhouse effect and it leads to global warming.