[gogeo]

Think about a greenhouse. A greenhouse is a little warmer than the average temperature of the ambient air. However, temperature fluctuation is moderated. That is, when it is cold outside, a greenhouse will only get cool. When it is hot outside, the greenhouse will only be warm...

Well, no...leave a car in the sun with the windows rolled up, and you'll have an example of the greenhouse effect.

[yefragetuwrabrumuy]

A greenhouse is a better example, because it is the humidity in the greenhouse that helps mitigate temperatures.

An enclosed car is more like a description of the gas laws, but with temperature as the only variable. Hotter outside equals hotter inside.

The atmosphere is not a limited, closed system. Half the Earth is in darkness when the other half is in light, and humidity and water, both in the air and bodies of water, can both reflect radiation back into space and trap it near the surface. High clouds tend to trap heat, and low clouds tend to reflect radiation back out into space.