Greenhouse Gases 101

http://en.wikipedia.org/wiki/Greenhouse_Gases

Ok the most potent is water vapour then methane next carbon dioxide there are others, but these are the main players. They let infra red radiation through from the sun but block the long wave radiation from being let out and so act as a blanket.

It heats up in the day and does not cool so fast at night. Cloudy nights are warmer. Water vapour traps the rising heat radiated from the ground, clear nights are more likely to be cold, even frosty. Carbon dioxide and methane also add to this effect.