Earth's Greenhouse Effect
Solar radiation is the major source of energy to Earth's surface. Much of that incoming short-wave-length energy is absorbed by the surface where it drives atmospheric and oceanic circulation, and fuels biological processes like photosynthesis. The land and sea surfaces then reradiate extra longer-wavelength heat, or infrared, energy. If Earth's atmosphere were transparent to the emitted infrared radiation, the planet would cool relatively efficiently and would have an average surface temperature of about 0°F (-18°C). However, the Earth's naturally occurring "greenhouse effect" maintains the planet's average temperature at a more livable 59°F (15°C) by trapping some of the escaping heat within the atmosphere. Small concentrations of so-called "green-house gases," also known as radiatively active gases, absorb some of the infrared energy and thereby delay its passage to space. Water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3) are the most concentrated and effective greenhouse gases. The greenhouse effect has been extremely important to the evolution and survival of life on Earth. A surface temperature of 59°F is sufficient to maintain the Earth's reservoirs of life-sustaining liquid water, and to impel climatic processes, whereas 0°F is too cold for most organisms to live or for ecological processes to function well.
Science EncyclopediaScience & Philosophy: Gastrula to Glow dischargeGlobal Warming - Earth's Greenhouse Effect, Atmospheric Concentrations Of Greenhouse Gases, Predictions And Evidence Of Global Warming