PrintGreenhouse Effect
Solar energy is emitted from the sun chiefly in the form of visible and short-wave infrared radiation. The portion of this radiation that is not reflected by cloud cover passes through the atmosphere of the earth and warms the surface of the land or sea. The surface of the earth, warmed by the sun, radiates heat back into the atmosphere. Water vapour and the other major "greenhouse gases" (GHG) such as carbon dioxide (CO2), methane (CH4), chlorofluorocarbons (CFCs), and, nitrous oxide (N2O), absorb a portion of the heat energy radiated from the earth's surface and warm the lower layer of the atmosphere (the troposphere). Some of this heat is directed back toward the ground, keeping it warmer than it would otherwise be. These gases surrounding the earth act much like the glass in a greenhouse, thus the phenomenon has been called the greenhouse effect. The greenhouse effect is a natural heat trapping mechanism that is essential to our existence on this planet. The moon, which does not have a protective blanket of air, has an average surface temperature of about -18°C. The moon is at almost the exact same distance from the sun as is the earth. Therefore it is safe to assume that the average temperature of the earth without the natural greenhouse effect would also be approximately -18°C. The average temperature of the earth surface is actually approximately 15°C. The blanket of air keeps the earth about 33°C warmer than it would otherwise be. As long as the amount of water vapour and other greenhouse gases in the air stays the same, and the amount of heat arriving from the sun is constant, an equilibrium is established. The present concern about the greenhouse effect began with the realization that human activities are increasing the amount of greenhouse gases in the atmosphere and thereby enhancing its ability to trap heat. The effect of increasing the concentration of greenhouse gases is that as each layer of the atmosphere absorbs more of the energy radiated from below, the temperature of the earth surface increases. Changes in temperature are expected to change weather patterns and the climate. Scientists use computer models to explore the possible consequences of rising temperatures throughout the world's weather systems. It is on the basis of theoretical climatic projections that scientists are concerned about the continuing build-up of greenhouse gases in the atmosphere.
