Greenhouse Effect

The greenhouse effect is a natural process that keeps the Earth's surface warm enough for life. Without it the mean surface temperature would be about −18 °C instead of about 15 °C.It works like this:
1. Short-wavelength radiation from the Sun (visible light and ultraviolet) passes through the atmosphere.
2. Some is reflected, but much is absorbed by the Earth's surface, which warms up.
3. The warm surface emits longer-wavelength infrared radiation.
4. Greenhouse gases in the atmosphere absorb some of this infrared radiation and re-emit it in all directions, including back towards the surface. This traps heat energy in the lower atmosphere.The main greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide (N₂O, released from fertilised soils) and CFCs. The effect of each depends on how much of the gas is present, how strongly each molecule absorbs infrared and how long it stays in the atmosphere.Human activities have raised the concentrations of carbon dioxide, methane and nitrous oxide. This produces the enhanced greenhouse effect: more infrared is trapped, so the mean global temperature rises. This is the main cause of current global warming.Note that the greenhouse effect is not the same as the hole in the ozone layer. Ozone depletion lets more ultraviolet reach the surface but is not the main cause of global warming.