Greenhouse Effect

Greenhouse Effect, term for the role the atmosphere plays in helping warm the Earth's surface. The atmosphere is largely transparent to incoming short-wave (or ultraviolet) solar radiation, which is absorbed by the Earth's surface. Much of this radiation is then re-emitted as heat energy at long-wave, infrared wavelengths; some of this energy escapes back into space, but much of it is reflected back by gases such as carbon dioxide, methane, nitrous oxide, halocarbons, and ozone in the atmosphere. This heating effect is at the root of the theories concerning global warming.

Under normal conditions the level of carbon dioxide in the atmosphere remains constant, and trees absorb the same amount of carbon dioxide that people produce. But in recent decades, our planet has supported more people and fewer trees, leaving an excess of carbon dioxide in the atmosphere. The amount of carbon dioxide has been increasing by 0.4 per cent a year; the use of fossil fuels such as oil, gas, and coal, and the slash-and-burn clearing of tropical forests have been contributing factors in the carbon cycle. Other gases that contribute to the greenhouse effect, such as methane and chlorofluorocarbons, are increasing even faster. The net effect of these increases could be a worldwide rise in temperature, estimated at 2° to 6° C (4° to 11° F) over the next 100 years. Warming of this magnitude would alter climates throughout the world, affect crop production, and cause sea levels to rise significantly. If this happened, millions of people would be adversely affected by major flooding.