The greenhouse effect is a process by which an atmosphere causes a planet to retain more heat than would be retained by a planet with no atmosphere.
To oversimplify a bit, what happens is that the sun's radiation (which is mostly at relatively high wavelengths – visible and ultraviolet) passes through the atmosphere relatively efficiently, but the corresponding radiation caused by the earth's increased heat (from absorption) is at longer wavelengths which are less efficiently transmitted (i.e. more efficiently absorbed). This causes the earth's surface to be warmer than it would be if it had no atmosphere.
In common parlance, the term "greenhouse effect" is sometimes used to refer specifically to enhanced absorption due to increased presence of greenhouse gases due to human activity, which is the primary theory by which global warming is attributed to human activities; "the greenhouse effect" is thereby sometimes misunderstood to be synonymous with "global warming".
- Skeptics of global warming (i.e. both those who disbelieve that it is occurring and those who disbelieve that it is attributable to human activities) often attempt to refute the greenhouse effect.
- Can the greenhouse effect be looked at as equivalent to painting the earth a darker color? Or is it somehow more extreme than that? This point isn't explained clearly. --Woozle 13:22, 9 July 2006 (EDT)