GREENHOUSE EFFECT, term for the role the atmosphere plays in helping warm the earth's surface. The atmosphere is largely transparent to short-wave solar radiation, which is absorbed by the earth's surface. Much of it is remitted at infrared wavelengths, and is in turn largely ab sorbed by carbon dioxide, methane, nitrous oxide, halocarbons, and ozone in the atmosphere and then remitted back toward the earthæhence the heating effect. The amount of carbon dioxide in the atmosphere has been increasing by 0.4 percent a year because of the use of oil, gas, and coal and the burning of tropical forests. Other gases that contribute to the greenhouse effect, such as methane and chlorofluorocarbons, are increasing even faster. The net effect of these increases may be a worldwide rise in temperature, estimated at from 2˚ to 6˚ C (4˚ to 11˚ F) over the next 100 years. Warming of this magnitude would not only alter climates throughout the world, it would also cause sea levels to rise at least 30 cm (12 in). If this happened, millions of people living in low-lying coastal areas would be affected.
