Global Warming

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.