Nature's Greenhouse Effect
The greenhouse effect is a natural process by which the Earth loses energy to space at wavelengths characteristic of infrared radiation. A number of trace gases in the atmosphere, in particular water vapour, carbon dioxide, methane and other gases such as the artificial CFCs (Chloro-fluoro-carbons), collectively known as "greenhouse gases", partially absorb and redistribute the outgoing terrestrial radiation within the atmosphere in the form of heat. Without this natural greenhouse effect, the Earth would be about 35°C colder than it is at present.
The human contribution
The enhanced greenhouse effect occurs because increases in the levels of certain greenhouse gases trap greater amounts of the infrared radiation emitted from the Earth's surface, raising the temperature of the atmosphere above its "natural" level. Rising levels of atmospheric carbon dioxide (CO2) and methane (CH4) concentrations are directly attributable to human activities. The enhanced greenhouse effect is often confusingly abbreviated to "Greenhouse Effect", and is also popularly referred to as "Global Warming" or "Climate Change".
Before the early 1800s, in the pre-industrial era, these gases fluctuated within fairly narrow limits over the previous 10,000-15,000 years. Since the 19th century, however, CO2 has increased by about 40% and CH4 by a factor of 3. The human contribution to increased CO2 levels stems mainly from the burning of fossil fuels (coal, oil, natural gas, and wood), while CH4 is linked largely to livestock production, particularly cattle. Most climate scientists believe that the enhanced greenhouse effect will lead to increases in atmospheric temperatures well beyond the range of natural climate fluctuations.
The Greenhouse Effect Shortwave radiation from the Sun reaches the Earth's surface, which emits energy into space as infrared radiation. Some energy is absorbed and re-emitted as heat into the atmosphere by greenhouse gases sensitive to the wave-lengths of the infrared spectrum